Clinical Usefulness of a Multigene Testing in Patients with Special Histologic Type Breast Cancer

Rare special histologic types of breast cancer usually show a favorable prognosis but often has atypical features. Multigene tests (MGTs) in patients with special types of breast cancer have not been well studied. Therefore, we aimed to examine the association between MGTs and histopathology and to evaluate the prognosis of MGTs in patients with special types of breast cancer.

A total of 133 patients with special histologic types of breast cancer who underwent MGTs were selected from two institutions from 2013 to 2022. Special types were divided into favorable and unfavorable groups. The patients' clinicopathological characteristics and MGT results were compared, and disease-free survival (DFS) was analyzed.

The unfavorable group consisted of 76 (57.1%) patients and included more older patients, multiple tumors, grade II/III tumors, high-risk MGT results, and chemotherapy administration. High-risk MGTs were found in 16.5% of the total cohort. The unfavorable type tended to have high-risk MGTs, but multivariate analysis demonstrated that grade II/III tumors, low progesterone receptor expression, and high Ki-67 levels were associated with high-risk MGTs in special type breast carcinomas. MGTs were significantly associated with DFS, particularly in the unfavorable subgroup, in which no recurrence occurred among patients with low-risk MGTs.

Unfavorable special types of breast cancer were more likely to have high-risk MGTs. The MGT result was a significant prognostic factor and could support decision-making for adjuvant therapies in patients with special histologic types of breast cancer.