POU2F2 May Be Predictive of Survival Benefit With Maintenance Avelumab in Urothelial Carcinoma

The absence of POU2F2, may be predictive of response to maintenance avelumab (Bavencio) in patients with advanced or metastatic urothelial carcinoma, according to findings from an analysis peripheral blood samples taken in the JAVELIN Bladder 100 trial (NCT02603432). POU2F2, a transcription factor with known roles in B-cell maturation and participation in T-cell dependent humoral immunity, was strongly associated with the T-effector signature.

“POU2F2 is a gene we don’t know a huge amount about,” Thomas B. Powles, MBBS, MRCP, MD, director, Barts Cancer Centre at St. Bartholomew’s Hospital in London said during the presentation of the data at the 2022 ESMO Congress. “Nevertheless, it does seem to be important regulation of B cells and may or may not be involved in tertiary lymphoid structures [TLSs].”

The analysis showed that POU2F2 expression in the tumor was linked to a survival benefit with maintenance avelumab. The benefit was highest in patients who had POU2F2 and a tumor mutation burden (TMB) above the median threshold of 7.66 nonsynonymous SNVs per Mb (HR, 0.69; 95% CI, 0.51-0.93).

Moreover, the absence of the POU2F2 loop in the blood samples was also associated with a better survival benefit associated with maintenance avelumab (HR, 0.62; 95% CI, 0.36-1.08).

Of note, Powles highlighted that the absence of the POU2F2 loop may pinpoint a benefit in patients who have a low TMB.

“Remember, these low TMB patients aren't supposed to be responding to therapy,” he said. “But indeed, if you have POU2F2 low, which is high gene expression, and low TMB, we can pick out a group of patients who are supposed to be the TMB low non-responders, and we can identify them as responders. And we can do this from blood tests, not from tissue, which I think is cool.”

The median survival probability for the 22 patients who received avelumab and did not have POU2F2, but a low TMB was 36.99 months versus 13.6 months in the 18 patients who only received best supportive care.

TLSs, ectopic lymphoid tissue that arises in inflamed tissues including cancer, have been generating quite a bit of interest, according to Powles.

“They’re characterized by B-cell and T-cell zones and are attracting attention in urothelial cancer,” Powles said. “They’re essentially balls of active immune cells … And [the] characterization of these tertiary lymphoid structures is an area of interest.”

To determine whether blood-based biomarkers could potentially provide insight into which patient populations may best benefit from immune checkpoint inhibitors such as avelumab, the investigators used the EpiSwitch platform to analyze white blood cell chromatin loops associated with tumor immune activity.

This analysis was conducted using peripheral blood samples that were collected from 496 patients enrolled onto the trial after non-progression with first-line chemotherapy and before patients were randomized to either avelumab plus best supportive care or best supportive care only.

One of the main questions posed by the investigators, according to Powles, was what role does POU2F2 play in determining patient outcomes and they looked for the chromatin loop in the blood as well as the genetic expression of the tumor.

“We looked at whole blood, we looked at PBMCs and we looked at the structure of chromatin,” Powles explained. “Chromatin has a really important role in DNA packaging. And it also therefore has a really important role in transcriptome extender and gene expression. The chromatin allows loops, these loops are associated with activation of transcription. And these loops can result in dynamic changes, of course, to protein expression.”

Powles stressed that there are several limitations with the trial, including that the analysis was exploratory in nature. Additionally, the investigators still need to validate the findings to confirm its feasibility to be used in the clinic.

Nonetheless, Powles concluded the presentation explaining the significance of the findings of the exploratory analysis of the peripheral blood samples.

“I think it’s reasonable to say that we showed TLS appear relevant in terms of outcome in the JAVELIN 100 trial,” he stated. “And these TLSs, along with the immuno signature helped us identify from the circulating white cells, POU2F2 as a key chromatin loop, and indeed gene expression, which may be relevant in predicting outcome for the future. … I think it's also reasonable to say that moving forward, the predisposition to form TLS in response to inflammatory stimuli may be a host factor influencing response to immune checkpoint inhibition, and therefore bringing the circulating and tumor-based biomarkers together is a really exciting area for the future.”

Reference

Powles T, Sridhar SS, Bellmunt J, et al. Genomic biomarkers in peripheral blood (PB) from patients (pts) enrolled in the JAVELIN Bladder 100 trial of avelumab first-line (1L) maintenance in advanced urothelial carcinoma (aUC). Ann Oncol. 2022;33(suppl 7):LBA74. doi:10.1016/annonc/annonc1089