Heterogeneity of triple-negative breast cancer: histologic subtyping to inform the outcome.

BACKGROUND: This study assesses outcome in terms of disease-free survival (DFS) and overall survival (OS) of special types of triple-negative breast cancer (TNBC). PATIENTS AND METHODS: We identified 8801 women with first primary nonmetastatic breast cancer operated on at the European Institute of Oncology between 1997 and 2005. Of these patients, 781 consecutive patients with immunohistochemically defined TNBC were selected for the analyses. We explored patterns of recurrence by histologic type. Median follow-up was 5.7 years (range 0-13 years).
RESULTS: The 5-year DFS was 77% for TNBC, 68% for human epidermal growth factor receptor 2 (HER2)-positive breast cancer, and 84% and 95% for luminal B and luminal A breast cancer, respectively. From 781 TNBC subtypes, 693 cases (89%) were classified as ductal not otherwise specified (NOS) (invasive ductal carcinoma [IDC]), 29 were classified as apocrine (3.7%), 18 (2.3%) were classified as lobular, 10 (1.2%) were classified as adenoid cystic, and 10 (1.2%) were classified as metaplastic. Five-year DFS and OS were 77% and 84% for patients with ductal carcinoma, 56% and 89% for patients with metaplastic carcinoma, and both 5-year DFS and OS were 100% for patients with adenoid cystic and medullary carcinomas, respectively.
CONCLUSION: Distinct prognostic implications may derive from the specific histotype of TNBC. The identification of these special types has a significant clinical utility and should be considered in therapeutic algorithms.