Breast tumors are often heterogenous, which can significantly affect treatment effectiveness. Biomarker assessment is a very useful tool often used to make treatment decisions. However, there is currently no established approach for biomarker reassessment after neoadjuvant systemic therapy (NAST), which may help guide future treatment. A study presented at the 2022 American Society of Clinical Oncology (ASCO) Annual Meeting found actionable changes in biomarkers before and after NAST.
The researchers conducted a retrospective review of 434 patients with breast cancer who received NAST and then had surgery between 2004 and 2020. All subjects’ tumors were tested for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status before NAST. After NAST, the same tests were run on residual tumor in 95 patients, representing 22% of the sample.
The researchers compared results between pre- and post-tests in that subgroup and found that 30 of the patients with repeat testing had different results after NAST. Changes in ER status occurred in 11 of 30 (36.7%), changes in PR status were found in 12 of 30 (40%), and changes in HER2 were discovered in 13 of 30 (43.3%). Those changes helped guide subsequent treatment decisions. A third of the patients with biomarkers that had changed went on to receive additional adjuvant treatment.
“Biomarker discordance due to tumor heterogeneity is an increasingly recognized phenomenon,” wrote the authors, led by Dan Ran Castillo, of Loma Linda Medical Center in California. “Given the prognostic and therapeutic implications of biomarker-driven breast cancer management, retesting biomarkers routinely after NAST on residual invasive tumor would be beneficial in this patient population.”