Dr McKenzie on Updates to ASCO Treatment Guidelines in Metastatic Breast Cancer

Andrew McKenzie, PhD, vice president, Personalized Medicine, Sarah Cannon Research Institute, scientific director, Genospace, discusses the updates to the ASCO clinical practice guidelines for biomarker testing in patients with metastatic breast cancer.

At an OncLive® State of the Science Summit™ on breast cancer treatment, McKenzie highlighted the most recent updates to the ASCO biomarker testing guidelines in breast cancer. The breast cancer treatment field is moving so rapidly that the ASCO guidelines published within the past year are already out of date, McKenzie says. ASCO recommends that oncologists test for PIK3CA mutations in patients with hormone receptor (HR)–positive metastatic breast cancer. Importantly, this testing can be conducted using either tissue-based or circulating tumor DNA–based next-generation sequencing technologies, McKenzie explains. The inclusion of both testing modalities in the guidelines demonstrates recognition of many patients with HR-positive breast cancer who have bone-only disease.

Outdated versions of the ASCO guidelines stated that there was insufficient evidence to support broad use of ESR1mutation testing outside of clinical trials, McKenzie expands. However, elacestrant is now FDA approved for patients with estrogen receptor (ER)–positive, HER2-negative, ESR1-mutated advanced or metastatic breast cancer, and patient eligibility for elacestrant depends on positive ESR1 expression per genetic testing, he says. As of March 2023, the ASCO guidelines were updated to recommend routine testing for ESR1 mutations at recurrence or progression on endocrine therapy in patients with ER-positive, HER2-positive metastatic breast cancer.

The ASCO guidelines also recommend germline testing for BRCA1/2 mutations in patients with HER2-negative breast cancer who may be eligible for PARP inhibitors. Furthermore, patients who are candidates for immune checkpoint inhibitors should undergo testing to determine PD-L1 or microsatellite instability status, he emphasizes. Additionally, the guidelines specify other molecular alterations that could be detected in breast cancers that should be tested for in patients with metastatic disease, McKenzie says.

Moreover, these guidelines recommend biopsies be done at progression and comprehensive germline and somatic profiling be used to identify candidates for additional targeted therapy, McKenzie continues. The variety of mutations that can drive breast cancer indicate a future shift away from traditional disease categories, such as HR-positive, HER2-negative, triple-negative, and HER2-positive, McKenzie concludes.