Genetic advances have helped elucidate the heterogenous nature of breast cancer, however optimal strategies for patients with early-stage disease still need to be ironed out. Surgery, systemic therapy, and radiation therapy are 3 therapeutic approaches to consider for patients with early-stage breast cancer according to current guideline recommendations.

 As more information about how breast cancer subtypes respond to treatment come to light, the clinical management of patients with early-stage disease is rapidly evolving.

Recent improvements in imaging, pathologic review, surgical techniques, and radiation design, combined with new information regarding tumor biology, has led to a more personalized approach for patients with ductal carcinoma in situ

). Investigators are examining watch-and-wait approaches as well as the use of neoadjuvant therapies prior to statandard of care surgery for patients with low-risk disease. Additionally, the use of pathological complete response (pCR) as a clinical end point has expanded access to treatment options for patients who may otherwise not benefit from delayed treatment.

It is estimated that 20% to 30% of DCIS will progress to invasive cancer. The long-term survival rate for patients with breast cancer treated for DCIS exceeds 95%.

 Treatment for DCIS has historically been based on studies of invasive breast cancer and includes a combination of surgery, radiation and hormonal therapy. However, deducing treatment strategies from these types of studies has been decried more recently by experts as overtreatment. This overdiagnosis and treatment based on mammographic screening are leading investigators to lean on strategies that employ a watch-and-wait approach.

“The 2 broad approaches for DCIS are (1) consideration of lumpectomy, and (2) mastectomy—especially if there is multicentric DCIS, meaning DCIS is in multiple parts of the breast,” said Aditya Bardia, MD, MPH, in an interview with 

For an individual lesion, DCIS breast-conserving therapy is an option, but if there are multiple DCIS lesions, doing multiple lumpectomies can be difficult. That’s where one could consider mastectomy,” said Bardia, an attending physician at Massachusetts General Hospital Cancer Center and an assistant professor of medicine at Harvard Medical School. “But you have to discuss these options with patient; mastectomy has its own psychological and physical consequences. Surgery can have complications as well. You have to carefully weigh risks and benefits.”

Overtreatment and uncertainty in standards of care

Controversy regarding DCIS overtreatment stems from demonstrated lack of mortality benefit, he explained. In an observational study, investigators analyzed breast cancer-specific mortality in a cohort of 108,196 women with DCIS. Among patients who received lumpectomy, radiotherapy was associated with a reduction in the risk of ipsilateral invasive recurrence at 10 years (2.5% vs 4.9%; adjusted HR, 0.47; 95% CI, 0.42-0.53; 

 < .001) but not of breast cancer—specific mortality at 10 years (0.8% vs 0.9%; HR, 0.86; 95% CI, 0.67-1.10; 

 = .22). Further, the 20-year breast cancerspecific mortality rate was 3.3%.

Patients who developed an ipsilateral invasive recurrence were 18.1 times more likely to die of breast cancer than women who did not. For patients who had a lumpectomy, the use of radiotherapy reduced the risk of developing an ipsilateral invasive recurrence from 4.9% to 2.5% but did not reduce breast cancer—specific mortality at 10 years (0.9% vs 0.8%). Similarly, patients who underwent unilateral mastectomy had a lower risk of ipsilateral invasive recurrence at 10 years than patients who underwent lumpectomy (1.3% vs 3.3%) but had a higher breast cancer–specific mortality (1.3% vs 0.8%). Patients who had a mastectomy had cancers with a larger mean size and higher grade than patients who had a lumpectomy.

“The question is, [when] you’re treating something, [you judge whether] is it important from the perspective that it will impair either survival or quality of life. That has been the conundrum with DCIS—that if someone has a mastectomy, [you wonder if there] was overtreatment. Maybe DCIS wouldn’t [have caused] problems for the rest of the life of the individual.

“The other scenario, [however,] is where somebody with DCIS will have the disease progress to invasive breast cancer, with even… [progression to] metastatic disease. [Clearly, that] could potentially impair quality of life and survival for the individual, and thus treating DCIS [more aggressively] makes sense in this scenario,” he said.

Currently, almost 70% of women with unilateral DCIS undergo breast conserving surgery, 20% undergo unilateral mastectomy, and about 10% elect for bilateral mastectomy.

To decrease the risk of ipsilateral breast tumor recurrence following surgery, the NCCN guidelines recommend endocrine therapy, noting that the benefit of therapy for patients with estrogen receptor—negative disease is uncertain. Several studies are investigating the use of neoadjuvant endocrine therapy for DCIS as potential alternative to surgery.

Median reductions from baseline MRI volume (1.4 cm

 < .001). Per study protocol patients underwent surgery following 6 months of treatment. Of the 59 patients, persistent DCIS remained in 50 patients (85%), invasive cancer was detected in 6 patients (10%), and no residual DCIS or invasive cancer was seen in 9 patients (15%). Investigators concluded that the findings support extended endocrine therapy as a nonoperative treatment option for some patients with DCIS.

With increased detection of DCIS, gene expression profiles are more commonly being used to identify patients who might be candidates for treatment deescalation.

 Risk stratification tools such as the Oncotype DX may aid in identifying patients who would benefit from more aggressive treatment. The 21-gene assay provides results as a risk score that can be used to refine treatment strategies for patients who are at low, intermediate, or high risk of recurrence or invasive disease in the subset of patients with DCIS.

For patients with low-risk DCIS, techniques for minimizing radiation exposure following breast conserving surgery are under way. Although radiation therapy is usually prudent as a component of breast conserving surgery in DCIS, selected low-risk patients may do best with the omission of surgery and adjuvant radiation therapy based on trial data.

The Comparison of Operative to Monitoring and Endocrine Therapy study, or COMET (NCT02926911), is a randomized study looking at guideline concordant care versus active surveillance.6 Investigators plan to enroll a total of 1200 patients with the primary outcome of evaluating the ipsilateral invasive breast cancer rate. Secondary objectives will be to compare surgical, oncological and patient-reported outcomes.

Patients in the guideline concordant care arm will undergo surgery as well as radiotherapy when appropriate. Patients in the active surveillance group will be monitored closely with surgery only on identification of invasive breast cancer. Endocrine therapy will be an available option to patients in both groups.

“While a bit controversial, clinical trials such as COMET are evaluating watchful waiting for low-risk DCIS. It is important to thoughtfully discuss treatment with patients and understand their preferences before finalizing treatment,” Bardia stated.

Using Prognostic Markers to Guide Treatment Decisions

Work still needs to be done to identify better markers to understand the link between tumor response, relapse risk, and diseasefree survival (DFS) and overall survival (OS). Samples collected from patients treated with neoadjuvant therapy are providing insights to the molecular basis to conclude more precise approaches to systemic treatments of breast cancer.

The use of Ki67 staining in patients with ER-positive breast cancer demonstrated efficacy as a marker for predictive of improved rates of breast conservation, the identification of extreme responders on the basis of preoperative endocrine prognostic index (PEPI) and provided rational to avoid chemotherapy on the basis of highly favorable prognosis in some patients.

Ki67 was utilized in the phase II neoMONARCH trial, which examined neoadjuvant therapy with the CDK4/6 inhibitor abemaciclib (Verzenio) plus anastrozole in patients with HR-positive/HER2-negative early-stage breast cancer. Results showed that the combination induced complete cell cycle arrest, which was the study’s primary end point, as measured by Ki67 for 67.8% of patients. For those treated with abemaciclib alone, cell cycle arrest was achieved for 57.7% of patients; for those who received anastrozole alone, 14.3% of patients experienced cell cycle arrest.

“In the HR-positive setting, a surrogate biomarker called [residual cancer burden] which is the change Ki67 [levels] from day 1 to 15, can provide surrogacy regarding long-term outcomes with NET [neoadjuvant endocrine therapy]. So, one could look at change in Ki67 as a biomarker end point to evaluate efficacy of NET in patients with HR-positive breast cancer,” Bardia said.

Several neoadjuvant trials have indicated that pCR correlates with long-term outcomes and is a proxy for DFS and OS. Highly proliferating carcinomas such as TNBC or HER2-positive tumors more commonly attain pCR readings than do luminal tumors.

 The term pCR refers to the lack of residual invasive cancer on histologic evaluation of the resected breast primary and regional lymph nodes following neoadjuvant therapy. For patients with early-stage breast cancer who are considered high-risk for distant disease recurrence and risk of death, the use of pCR an measure of clinical efficacy may predict clinical benefit within several months of treatment, addressing unmet treatment needs in a shorter timeframe compared to conventional therapies.

“The presence of pCR after neoadjuvant chemotherapy is associated with better outcomes as compared with patients who do not have a pCR. So, it is a robust prognostic biomarker,” said Bardia said.

In 2014, the FDA listed pCR as an acceptable surrogate end point of clinical benefit in neoadjuvant clinical trials in which agents were undergoing accelerated drug approval.

However, for HR-positive disease treated with neoadjuvant chemotherapy or endocrine therapy, high pCR rates are infrequent; therefore, other biomarker end points have been suggested, such as residual cancer burden, tumor size, and nodal status to provide a surrogate estimate of disease recurrence risk.

National Comprehensive Cancer Network. Clinical Practice Guidelines in Oncology. Breast Cancer (version 2.2020). nccn.org/ professionals/physician_gls/pdf/breast.pdf. Accessed February 20, 2020.

Doke K, Butler S, Mitchell MP. Current therapeutic approaches to DCIS. 

. 2018;23(4):279-291. doi: 10.1007/s10911-018-9415-1.

Hwang ES, Malek V. Estimating the magnitude of clinical benefit of local therapy in patients with DCIS. 

. 2019;48(suppl 1):S34- S38. doi: 10.1016/S0960-9776(19)31120-8.

Narod SA, Iqbal J, Giannakeas V, Sopik V, Sun P. Breast cancer mortality after a diagnosis of ductal carcinoma in situ. 

. 2015;1(7):888-896. doi: 10.1001/jamaoncol.2015.2510.

Hwang ES, Hyslop T, Hendrix LH, et al. Phase II single-arm study of preoperative letrozole for estrogen receptor—positive postmenopausal ductal carcinoma in situ: CALGB 40903 (Alliance) [published online ahead of print March 3, 2020]. 

Hwang ES, Hyslop T, Lynch T, et al. The COMET (Comparison of Operative versus Monitoring and Endocrine Therapy) trial: a phase III randomized controlled clinical trial for low-risk ductal carcinoma in situ (DCIS). 

. 2019;12:9(3):e026797. doi: 10.1136/ bmjopen-2018-026797.

Reinert T, Gonçalves R, Ellis MJ. Current status of neoadjuvant endocrine therapy in early stage breast cancer. 

. 2018;19(5):23. doi: 10.1007/s11864-018-0538-9.

Martin M, Hurvitz SA, Chan D, et al. Final results of NeoMONARCH: A phase 2 neoadjuvant study of abemaciclib in postmenopausal women with hormone receptor positive (HR+), HER2 negative breast cancer (BC). Presented at: the 2017 San Antonio Breast Cancer Symposium; Dec. 5-9, 2017. Abstract PD5-01.

Chaudhary LN, Wilkinson KH, Kong A. Triple-negative breast cancer: who should receive neoadjuvant chemotherapy? 

. 2018;27(1):141-153. doi: 10.1016/j.soc.2017.08.004.

Table of surrogate endpoints that were the basis of drug approval or licensure. FDA website. www.fda.gov/drugs/developmentresources/ table-surrogate-endpoints-were-basis-drug-approval-orlicensureUpdated September 30, 2019. Accessed February 20, 2020.

View more from the 2020 Miami Breast Cancer Conference

In a phase II single-arm study, postmenopausal patients with estrogen receptor (ER)-positive DCIS were treated with aromatase inhibitor letrozole (Femara) 2.5 mg/day for 6 months prior to surgery. Breast MRIs were conducted at baseline, 3 months, and 6 months with a primary end point of change in MRI volume of disease. Of 79 patients enrolled, 67 had data available at analysis. Significant imaging and biomarker changes were observed.

The National Comprehensive Cancer Network (NCCN) guideline for patients who receive a diagnosis of DCIS following mammography recommend lumpectomy without lymph node surgery with or without radiation therapy (whole breast or accelerated partial breast); or total mastectomy with or without sentinel node biopsy and optional reconstruction (

Articles

Genetic advances have helped elucidate the heterogenous nature of breast cancer, however optimal strategies for patients with early-stage disease still need to be ironed out.

Navigating Treatment Options for Patients With Early-Stage Breast Cancer

Although PD-L1 expression is the most established yardstick of response to immune checkpoint immunotherapy, its clinical utility as a biomarker remains an enigma further complicated by the variety of assays and algorithms for measuring it, experts say.

The implications of PD-L1 expression as a predictor of response to immune checkpoint inhibitors (ICIs) have been the subject of exploration and debate ever since the early development of therapies targeting the PD-1/ PD-L1 pathway.

Nevertheless, several immunohistochemistry (IHC) assays have been developed to detect PD-L1 expression levels for specific drugs; each biologic has its own IHC assay specific to a distinct anti—PD-L1 antibody clone and a distinct staining platform with specific tumor cell or immune cell thresholds.

Questions about the interchangeability of available assays have emerged, most recently in analyses of expression levels in patients with triple-negative breast cancer (TNBC) considered for treatment with atezolizumab (Tecentriq), a PD-L1 inhibitor.

 Other experts have expressed concern about the impact that using assays that have been developed so specifically for particular therapies could have on clinical practice.

“It’s unfortunately a mess that’s been conferred to us by vendors having different assays,” David Rimm, MD, PhD, director of both pathology tissue services and translational pathology at Yale School of Medicine in New Haven, Connecticut, said in an interview with 

“If they all had the same assay, we would see both tumor and immune cell staining in every tumor type. It’s crazy—we’re just trying to measure the same protein. The same assay should work on all the different cancer cells,” he said. “This is the first time in history that we’ve been told to use this company’s assay for this tumor and a second company’s assay for a second tumor. It’s a very bad idea.”

As it stands, PD-L1 expression testing using an FDA-approved companion diagnostic is required for several label indications for 2 ICIs, pembrolizumab (Keytruda) and atezolizumab (

Even without a label indication, however, clinical studies of ICIs routinely evaluate responses by PD-L1 status as a stratification factor. “Careful interpretation of PD-L1 expression data may unmask poor risk groups who may not benefit from [immuno- oncology] drugs,” Kevin Harrington, PhD, a professor at The Institute of Cancer Research (ICR) in London, England, said in a presentation at the European Society for Medical Oncology 2019 Annual Congress.

“This is really critical—that we don’t get swept away by the idea that everyone should get a PD-1 or a PD-L1 inhibitor first, when it is approved in the first line, because there may be patients who clearly don’t benefit from those therapies,” added Harrington, who also is the joint head of the Division of Radiotherapy and Imaging at ICR.

Overall, 5 IHC assays have been developed for pivotal clinical trials involving currently approved ICIs targeting the PD-1/PD-L1 pathway: Ventana PD-L1 (SP142) for atezolizumab, Dako 73-10 for avelumab (Bavencio), Ventana PD-L1 (SP263) for durvalumab (Imfinzi), IHC 28-8 pharmDx for nivolumab (Opdivo), and IHC 22C3 pharmDx for pembrolizumab (

 For the sixth approved ICI, cemiplimab-rwlc (Libtayo), a PD-1—directed antibody indicated in cutaneous squamous cell carcinoma settings, PD-L1 expression was evaluated in a small subset of patients in the pivotal trial but did not correlate with outcomes.

Clinical decisions about which PD-L1 testing assay to order depend upon the patient’s cancer type and stage and the ICI under consideration, according to ARUP Consult, an online laboratory test selection tool sponsored by the University of Utah Department of Pathology.

The availability of multiple assays is particularly noticeable in non—small cell lung cancer (NSCLC). “We’re in a bit of a conundrum at the moment in terms of the number of assays and the number of different technologies that are being used to assess PD-L1 staining,” Harrington said during his presentation. “For each of these different drugs with 4 different manufacturers, 4 different antibodies, there is the potential that there may be discrepancy and discordance.”

, Cottrell and Taube highlighted practical issues with having various PD-L1 assays. “The approval of multiple assays associated with unique interpretation thresholds has made it difficult to directly compare results across clinical trials. It has also created many practical concerns regarding which test to use and the interchangeability of the results,” they wrote.

The authors go on to note that the assays 22C3, 28-8, and SP263 are comparable in their ability to detect PD-L1, whereas SP142 has a reduced sensitivity.

 Of note, SP142 was used in the IMpassion130 trial for patients with TNBC.

“It was shown that there is a greater degree of variability in scoring of immune cell PD-L1 expression across all 4 assays,” wrote the authors, “likely due to a lack of defined criteria and a lack of training, contributing to poor reproducibility amongst pathologists.”

The authors also described how IHC assay systems can differ in their ability to detect PD-L1 expression, and based on studies showing that different PD-L1 antibodies stain equally well in NSCLC and melanoma, they hypothesize other factors are at play, such as antigen retrieval, concentration of primary antibody, and amplification.

Table 1. ICI Indications Linked to PD-L1 Expression

In an interview, FDA officials explained the agency’s support for approving multiple assays. “Different cancer types have different levels of PD-1/PD-L1, both on the surface of the tumor cells and on immune cells that surround the tumor cells,” an FDA spokesperson said in an email. “Each pharmaceutical company that develops PD-1/PD-L1-targeted therapeutics also determines the optimal scoring [level of PD-1/PDL1] based on patient response to their specific therapeutic.

“While the different FDA-approved tests may detect the same biomarker, the performance characteristics of these tests differ, which means they may identify different patient populations, as they are based on the data generated in the course of the corresponding therapeutic trial,” the spokesperson said. “Thus, a test is uniquely paired with a specific drug, and FDA approval of this drug-device pair has been shown to be safe and effective for the stated intended use, including the specific indication.”

A Roche spokesperson explained the rationale behind the development of the PD-L1 assay that Genentech, a member of the Roche Group, has used in studies of atezolizumab. “Immunotherapy biomarkers are fundamentally different from oncogene biomarkers in that they are continuous rather than categorical (binary)—spatially and temporally variable and reliant on multiple complex interactions rather than a single, dominant determinant,” the Roche spokesperson said.

Table 2. IHC PD-L1 Assays Developed for Clinical Trials of Approved ICI Therapies

PD-L1, a ligand of the PD-1 receptor, is a dynamic marker that interacts with PD-1 to suppress the immune system’s response to cancer, but its expression can predict a favorable response to antibodies designed to unfetter antitumor activity. The predictive value of PD-L1 expression varies depending on the tumor type; in some NSCLC indications, for example, its expression on malignant cells is characterized as a robust predictor of response, whereas its impact in other cancers is less clear.

Lymphocytes, including T cells, B cells, and natural killer cells, express the PD-1 receptor. On the other hand, PD-L1 is expressed on more cell types in addition to lymphocytes, such as tumor cells, macrophage-lineage cells, and endothelial cells.

Testing immune cells for PD-L1 expression differs from traditional IHC tests that examine tumor cells, Rimm noted. “As pathologists, we look at the cell type that expresses PD-L1,” he said. “PD-L1 can be expressed by actual tumor cells because they have a certain morphologic and biologic appearance. It can also be expressed by immune cells, which is a basket term for lymphocytes, macrophages, dendritic cells, myeloid-derived stem cells, and other cells that are not tumor cells but are in the microenvironment of the tumor or stroma.” Grouped together, those less common cells are called immune cells, he said.

Importantly, different tumor types have been noted to exhibit different proportions of immune cell and tumor cell stain, Rimm said. For example, breast cancer and head and neck cancer tumors stain heavily for immune cells compared with tumor cells, whereas lung cancer stains more heavily for tumor cells.

The FDA explained its approach to scoring criteria: “Based on the PD-L1 device, scoring criteria may include the assessment of PD-L1 staining in tumor cells, immune cells, or both at specific percentage levels (cutoff). FDA requests and reviews the analytical performance of the IHC test across all critical steps to determine that the test is robust and informative for the specific use. An important part of the FDA review includes the review of the inter-reader precision where the performance of multiple pathologist readers [is] evaluated.”

The availability of multiple PD-L1 assays and the appropriate choice for ICI therapy has surfaced in TNBC. In March 2019, atezolizumab became the first ICI to gain an indication for breast cancer when the FDA approved the drug in combination with nab-paclitaxel (Abraxane) for patients with unresectable locally advanced or metastatic PD-L1—positive TNBC.

The drug was approved based on findings from the phase III IMpassion130 trial, which showed an improvement in median progression-free survival (PFS) of 7.4 months with atezolizumab/nab-paclitaxel versus 4.8 months with chemotherapy (HR, 0.60; 95% CI, 0.48-0.77; 

 In the study, PD-L1 positivity was defined as PD-L1 stained tumor-infiltrating immune cells of any intensity covering ≥1% of the tumor area using the SP142 assay.

In an exploratory overall survival (OS) analysis, patients with PD-L1—positive tumors, median OS was 25.0 months (95% CI, 19.6-30.7) with atezolizumab versus 18.0 months (95% CI, 13.6-20.1) with placebo. The difference was not statistically significant according to the study’s prespecified parameters, but investigators said the benefit with atezolizumab therapy was clinically meaningful (stratified HR, 0.71; 95% CI, 0.54-0.94).

Mathematical modeling has been unable to harmonize PD-L1 expression findings from the SP263 and 22C3 PD-L1 assays with the FDA-approved SP142 companion diagnostic, according to an exploratory analysis of the IMpassion130 trial presented at the 2019 San Antonio Breast Cancer Symposium.

 Accordingly, “the assays cannot be considered equivalent,” leaving the SP142 assay as “the only clinically validated companion assay to select patients with metastatic TNBC for treatment with atezolizumab plus nab-paclitaxel,” lead study author Hope S. Rugo, MD, FASCO, and coinvestigators wrote in the conclusion of their poster.

In earlier data, Rugo and colleagues retrospectively scored tumor samples from participants in the study, with the 3 assays using central testing read by pathologists trained and qualified to read immune cells ≥1% (SP142 and SP263) and combined positive score (CPS) on tumor plus immune cells ≥1 (22C3).

“The different assays identified different percentages of cases that are positive for PD-L1,” said Rugo, professor of medicine and director of Breast Oncology and Clinical Trials Education at the University of California, San Francisco, Helen Diller Family Comprehensive Cancer Center. “More tumors were classified as positive for PD-L1 using the 2 alternative antibodies and assays [81% with 22C3 and 75% with SP263].

“Almost all SP142-positive cases are captured by either 22C3 CPS or SP263,” she said. “However, about one-third of patients’ tumors were positive for PD-L1 using only 1 of [these] 2 assays. The overall percentage of agreement between SP142 and 22C3 was 64% and between SP142 and SP263 was 69%.”

The biomarker-evaluable population (BEP) consisted of 614 patients, representing 68% of the intention-to-treat (ITT) IMpassion130 population. In this cohort, 46% were PD-L1- positive using SP142 versus 41% in the ITT population. The improvement in PFS with the addition of atezolizumab was slightly greater in the BEP than in the ITT group.

The median PFS was 8.3 months with the atezolizumab regimen versus 4.1 months with nab-paclitaxel plus placebo in the PD-L1—positive BEP population. In the PD-L1– positive ITT population, the median PFS was 7.5 months versus 5.3 months, respectively. Rugo et al noted that the benefit for the atezolizumab regimen was driven by the SP142 subgroup.

Although Roche understands the value of having fewer tests, the company said its goal with the SP142 assay was to best predict outcomes of therapy. “An amplification detection system was incorporated to visually enhance the assessment of PD-L1 particularly on immune cells. This is currently the only commercially available PD-L1 assay which is amplified and consequently has a different staining pattern to other approved PD-L1 assays,” the company spokesperson said. “This has created challenges for pathologists seeking to harmonize these assays so that they can use 1 PD-L1 assay to make therapeutic decisions for several different PD-1 and PD-L1 inhibitors across several different indications based on different scoring algorithms.

“Although the desire for streamlining of testing is understood, the role of a companion diagnostic assay is to discriminate between responders and nonresponders for that specific therapeutic product in a specific indication, with a cutoff based on clinical outcomes,” the Roche spokesperson stated.

Leading investigators into NSCLC were among the first cancer researchers to confront the question of interchangeability in PD-L1 assays. Starting in 2015, industry and academic leaders have been working on harmonizing tests to evaluate patients with the malignancy for ICI therapy. In 2018, Tsao et al published findings from the second phase of the Blueprint (BP) Programmed Death Ligand 1 (PD-L1) Immunohistochemistry Comparability Project (BP2).

In BP2, pulmonary pathologists from 15 countries scored specimens with the 5 assays used in NSCLC studies (

). Staining with the 22C3, 28-8, and SP263 assays was “highly comparable,” the investigators said. When detecting PD-L1 expression on tumor cells, they calculated lower sensitivity with SP142 and higher sensitivity with 73-10. Additionally, the results showed that scoring by pathologists was strongly reliable for tumor cells with all assays (overall intraclass correlation coefficient [ICC], 0.86-0.93) but poor reliability on immune cells (overall ICC, 0.18-0.19).

Similarly, in a study sponsored by the National Comprehensive Cancer Network Oncology Research Program and Bristol- Myers Squibb, Rimm and colleagues found that in 4 commercial assays for NSCLC, the ICC for tumor cell testing was high: 0.83-0.88 for each antibody. However, ICC from immune cells for each antibody was 0.17-0.23. Again, this study involved multiple raters.

In the interview, Roche responded to questions about reproducibility with regard to its SP142 assay.

“The analytical characteristics of the Ventana PD-L1 (SP142) Assay, including inter-reader repeatability and reproducibility, have been published together with the effectiveness of pathologist training on the assessment of Ventana PD-L1 (SP142) Assay staining on both tumor cells (TCs) and tumor-infiltrating immune cells (ICs) in non— small cell lung cancer and urothelial cancer tissues, demonstrating that the assay reliably evaluated staining on both TC and IC across multiple expression levels/clinical cut-offs,” said the Roche spokesperson.

For its part, the FDA indicated that reproducibility with approved assays is not an issue. “PD-L1 devices and the associated scoring algorithms are developed based on data from clinical trials. For certain PD-L1 devices/drugs, data show that assessment of PD-L1 staining in [immune cells] is related to clinical outcome. Moreover, the assay reproducibility has been demonstrated in the course of FDA’s review to be sufficiently robust to identify a population of people who benefit from the drug in a clinical trial.”

Differences in test results vary in other cancers. In a meta-analysis, Torlakovic et al looked for equivalence among commercially available assays across 22 studies and 376 assay comparisons, all with various thresholds. Most of the test comparisons (337) were for NSCLC; other tests were for urothelial carcinoma, mesothelioma, and thymic carcinoma.

Due to the nature of the studies, investigators were limited to 2 metrics used in most studies: 1% and 50% cutoffs for tumor proportion score. Comparisons were made between the 22C3, 28-8, and Ventana SP263 assay.

SP263 had the highest sensitivity and lowest specificity of tested assays, followed by 28-8, and 22C3. With respect to interchangeability, if this term were defined as 90% sensitivity and specificity for both cutoffs, no assay would be considered interchangeable. Nevertheless, the assays’ results are comparable, investigators said.

Notably, the investigators concluded that if an FDA-approved companion diagnostic is not available for PD-L1 expression analysis, “it is better to develop a properly validated laboratory-developed test for the same purpose(s)” than it is to substitute another companion diagnostic.

In findings presented at the 2019 American Society of Clinical Oncology Annual Meeting, Labriola et al compared the 28-8 and SP142 IHC assays in 32 patients with metastatic renal cell carcinoma (mRCC) and 18 with metastatic urothelial carcinoma (mUC). Findings showed that 91% of mRCC cases reflected agreement between the 2 assays, with 94% concordance for mUC based on tissue samples.

“Although PD-L1 status does not fully predict for response to ICIs, this suggests that PD-L1 testing could be used interchangeably for the majority of cases when selecting ICI treatment in mRCC and mUC,” investigators concluded.

In addition to variability in assay performance and interpretation, there are other challenges with measuring PD-L1 expression.

First, no distinction between adaptive and constitutive patterns of PD-L1 expression are made in guidelines. Adaptive PD-L1 expression is a heterogeneous interferon gamma—driven mechanism of PD-L1 expression by tumor and immune cells at the host-tumor interface, whereas constitutive tumor cell PD-L1 expression refers to expression of PD-L1 on the cell surface of tumor cells regardless of the presence of an immune infiltrate and could be mediated by multiple mechanisms stemming from genetic mutations.

The occurrence of constitutive PD-L1 expression apparently differs based on tumor type, with melanoma—in which adaptive expression was first discovered&mdash;displaying infrequent expression and cutaneous squamous cell carcinoma exhibiting more expression. Although adaptive and constitutive expression are not mutually exclusive, it could be that in the absence of a triggering immune response, constitutive expression does not predict response to therapy with anti-PD-1/PD-L1 inhibitors, as is the case with squamous cell cancers of the head and neck cancers, a tumor type for which response to anti-PD1/PD-L1 therapy appears to be predicted by immune cells.

Second, the expression of PD-L1 over time could change due to its heterogeneous and focal nature. On a related note, tissue samples for evaluation could be too small.

Third, other resistance mechanisms could be present in the tumor that interfere with response to treatment, such as alternate PD-1/PD-L1 ligand/receptor activity (PD-L2, B7-1/CD80) or expression of other checkpoint molecules.

Investigators are on the hunt for alternative biomarkers that would indicate the potential efficacy of anti-PD-1/PD-L1 therapy. These approaches include measuring tumor infiltrating lymphocytes (TILs), assays that analyze PD-L1 expression plus TILs, tumor mutational burden, circulating tumor and immune cells, and microbiome-rich stool.

Pharmaceutical companies also are moving forward with studies of emerging markers. “Two-thirds of our research and development projects are being developed with companion diagnostics, and Roche Tissue Diagnostics is a leader in CDx development,” the company spokesperson said. “The development of each targeted therapeutic candidate includes the assessment of biomarkers that may be associated with response to treatment. We continue to further our understanding of cancer and explore innovative diagnostic approaches, including new technologies in digital pathology and multiplex testing innovation.”

For Rimm, improvement of biomarker testing for immune-oncology agents is a pressing research priority. “Every pathologist doing their job right wants the best thing for the patients. We don’t interact with the patients; we only interact with the oncologists on a regular basis,” he said. “Our oncologists are completely at a loss for what they should do. They just want us to tell them if it’s positive or negative. We need to come up as quickly as possible with another approach to addressing this issue.”

“Different PD-1/PD-L1 inhibitors that have included a specific PD-L1 assay have assessed varying levels of PD-L1 expression in clinical trials for correlation with clinical outcomes. Consequently, there are different scoring algorithms and cutoffs for different assays as companion diagnostic assays for different drugs in different indications.”

Ionescu et al express similar concerns in a review article in 

. “Given the likely future availability of additional PD-L1 inhibitors, PD-L1 assays will become increasingly important in identifying patients most likely to benefit from treatment. However, the PD-L1 assays for use with durvalumab, pembrolizumab, nivolumab, and atezolizumab have all been developed independently, and they use different antibody clones, immunohistochemistry staining protocols, scoring algorithms, and cutoffs for determining PD-L1 status. Questions have therefore been raised about whether the tests can be used interchangeably to inform treatment decisions for the various PD-1 and PD-L1 inhibitors.”

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Although PD-L1 expression is the most established yardstick of response to immune checkpoint immunotherapy, its clinical utility as a biomarker remains an enigma further complicated by the variety of assays and algorithms for measuring it.

Naveed Saleh, MD, MS

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