Relevance of the 21-gene expression assay in male breast cancer: A systematic review and meta-analysis.

Introduction: The 21-gene assay provides prognostication for estrogen receptor positive, human epidermal growth factor receptor-2 negative (ER+/HER2-) early female breast cancer patients. This signature has not been validated in male breast cancer (MBC).

Methods: A systematic review and meta-analysis was performed in accordance to the PRISMA guidelines.