Clinicopathological Features of Breast Cancer with Polysomy 17 and Its Response to Neoadjuvant Chemotherapy

Objective: The interpretation of human epidermal growth factor receptor 2 (HER2) fluorescence in situ hybridization (FISH) results may be challenging in tumors with polysomy 17, which is defined as increased signals of chromosome enumeration probe 17 (CEP17). The effect of polysomy 17 on HER2 protein expression and tumor treatment response has not been established. In this retrospective study, we investigated the clinicopathological features of breast cancer with polysomy 17 and determined the tumors' response to neoadjuvant chemotherapy (NACT).

Materials and methods: The study included 366 patients with primary breast cancer whose tumors had a CEP17 count of ≥ three/nucleus based on HER2 FISH studies. These cases were categorized according to HER2/CEP17 ratio and HER2 signals/nucleus using the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines. We compared the clinicopathological characteristics and tumor response to NACT among different groups.

Results: There was a statistically significant difference in patients' age at diagnosis, tumor pathological grade, estrogen and progesterone receptor status, and NACT response among different HER2 FISH groups. Polysomy 17 tumors in group 1 had a higher rate of response (pathological complete response and residual cancer burden class I) to NACT containing anti-HER2 reagent than did those in other groups (p = 0.004), whereas polysomy 17 tumors in group 3 did not show a significant response to anti-HER2 treatment.

Conclusion: Polysomy 17 tumors in different HER2 FISH groups have different pathological features and respond to NACT differently. These results may help us identify patients who will benefit from anti-HER2 therapy.