乳癌の浸潤癌（特殊型なし）におけるメジュラリー癌型におけるヒト上皮成長因子受容体2およびアンドロゲン受容体発現

Invasive breast carcinoma of no special type with medullary pattern (BCNST-MP) is a rare subtype of breast cancer. Previous studies have reported the high prevalence of the triple-negative phenotype in BCNST-MP. This study aimed to investigate the prevalence of human epidermal growth factor receptor 2 (HER2)-low and androgen receptor (AR) expression in this distinct breast cancer subtype.

We conducted a retrospective analysis of breast cancer patients diagnosed at our center between 2019 and 2024. Medical records and pathology reports were reviewed to assess the clinicopathological characteristics of BCNST-MP.

A total of 45 patients with BCNST-MP met the inclusion criteria. The median age at diagnosis was 51 years. Most tumors (93.3%) measured ≤5 cm, and axillary lymph node metastasis was observed in 26.7% of cases. Eighty percent of the patients were estrogen receptor (ER)-negative, 84% were progesterone receptor (PR)-negative, and 75.6% were AR-negative. Regarding the HER2 status, 15.6% were HER2-positive, 33.3% exhibited HER2-low expression, and 51.1% had HER2-zero expression. With a median follow-up duration of 26 months, only one patient-a 30-year-old with triple-negative breast cancer-developed distant metastasis. An 82-year-old died of a cerebrovascular accident.

Our findings suggest that BCNST-MP tumors are rarely larger than 5 cm and are frequently lymph node-negative. Most patients were negative for ER, PR, AR, and HER2. Notably, HER2-low expression was observed in approximately 30% of cases, suggesting therapeutic implications.