Apocrine metaplasia of breast cancer: clinicopathological features and predicting response

Tailor-made therapies are currently gaining prominence, and the clarification of predictive markers for anticancer agents represents an important research issue. From our institutional neoadjuvant experience, apocrine carcinoma showed a high correlation with therapeutic effect against breast cancer. We thus considered that apocrine metaplasia (AM) might represent a predictive marker for breast cancer.

A total of 210 primary invasive breast cancers from Japanese patients were scored according to the size of cytoplasmic granules and abundance of cytoplasm, then classified into three categories: non-AM, incomplete AM and complete AM. Clinicopathological features were evaluated based on these classifications.

Distribution according to the classification of AM was: non-AM, 61%; incomplete AM, 36%; and complete AM, 3%. No significant differences with regard to estrogen receptor, progesterone receptor, human epidermal growth factor receptor type 2, androgen receptor or bcl-2 were observed among the three groups. Gross cystic fluid protein-15 showed a high positive rate (83%) for complete AM. Cases of incomplete AM and complete AM were combined to form the AM group. Among lymph node-positive patients without chemotherapy, the 10-year recurrence-free survival (RFS) rate was 85% for non-AM and 44% for AM (p < 0.05). Conversely, among the lymph node-positive group with chemotherapy, the 10-year RFS rate was 45% for non-AM and 75% for AM (p < 0.05). Prognoses for non-AM and AM were turned around by chemotherapy. Lymph node metastasis was related to prognosis in multivariate analysis, although AM did not remain an independent prognosticator.

Apocrine metaplasia appears to offer an effective predictive marker for anticancer therapy.