Metaplastic breast carcinoma (MBC) is a rare subtype of breast cancer with variable morphology. MBC is more often triple negative (ER-, PR-, HER2-) and is associated with poorer clinical outcome when compared with infiltrating ductal carcinoma. The purpose of our study is to identify molecular alterations in MBC using next-generation sequencing (NGS), which may aid chemotherapy selection and use of targeted therapy. A cohort of 18 patients with MBC yielded adequate DNA from microdissected formalin-fixed and paraffin-embedded tumor blocks. NGS was performed using the Ion AmpliSeq cancer hotspot mutation panel version 2 kit, which targets hotspot regions in 50 genes. Immunohistochemical stains for androgen receptor (AR), and programmed cell death ligand-1 were performed. A total of 23 genetic alterations were identified in 15 (83.3%) of 18 patients. Eleven genetic alterations in the PI3K signaling pathway were identified in 9 (50.0%) of 18 patients, including 7 PIK3CA mutations (38.9%), 3 PTEN genetic alterations (16.7%), and 1 AKT1 mutation (5.6%). Ten (55.6%) of 18 patients each harbored 1 TP53 genetic alteration. Additional genetic alterations identified were 1 HRAS mutation and 1 ATM mutation. AR immunoreactivity was identified in 2 (11.1%) of 18 patients. Programmed cell death ligand-1 was negative in all patients. NGS analysis demonstrated that PI3K pathway-related genetic alterations were detected in a high percentage of MBCs, suggesting that targeting the PI3K/mTOR pathway may be promising in patients with MBC. In addition, patients with AR expressing MBC may benefit from androgen antagonist treatment.
Keywords: Androgen receptor; Metaplastic breast carcinoma; Next-generation sequencing; PD-L1; PI3K pathway; Triple negative.
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