Tumor copy number alterations were associated with primary endocrine resistance in ER+ breast cancer.

Abstract

e12567 Background: Several studies has showed alterations in genes were associated with endocrine resistance in breast cancer. Nevertheless, genomic landscape in primary endocrine-resistant breast cancer has not been thoroughly reported. Whether the genomic landscape of primary endocrine-resistant breast cancer is different from that of secondary endocrine-resistant breast cancer is unknown. Methods: We analyzed the genomic landscape of primary tumor of consecutive patients with estrogen-receptor positive (ER+) breast cancer in real-world clinical practice in our center between September, 2019 to December, 2020. According to the duration of endocrine treatment, we classified them into primary endocrine resistance group and secondary endocrine resistance group. Results: A total of 41 tumor samples of which 25 cases in primary endocrine resistance and 16 cases in secondary endocrine resistance were included for analysis. TP53 (65.9%, 27/41), PIK3CA (46.3%, 19/41), MYC (36.6%, 15/41), MCL1 (31.7%, 13/41), CCND1 (31.7%, 13/41) were the most frequently altered genes in all 41 BCs. Copy number amplification of MYC was common in primary endocrine resistant group (48.0%, 12/25), while lower in secondary endocrine resistant group (18.8%, 3/16, P = NS). Copy number alteration (CNA) of CCND1, MCL1, FGF19, ZNF217, ZNF703 and FGFR1 were commonly observed in primary endocrine resistance group. Percentage of CNA in all mutation types was significant increased in primary endocrine resistance group than in secondary resistance group (33.0% vs. 21.0%, P = 0.03). Then we further analyzed and found CNA burden, which was defined as number rather the percentage of the CNA event, was associated with the prognosis in ER+ breast cancer. When defining 6 as the cut-off value of CNA-High, DFS, PFS and OS were practically poorer in patients with CNA-High than those with CNA-Low. Conclusions: Copy number alterations were more commonly seen in primary endocrine-resistant breast cancer and associated with prognosis in ER+ breast cancer. This founding urged to further investigate the prognostic value of CNA burden in predicting the effectiveness of endocrine therapy.