Updated project metadata. Mammary secretory carcinoma (MSC) is one of the rarest types of breast cancer accounting for less than 0.15% of all breast cancers. Traditionally, MSC is considered that it belongs to the phenotypic spectrum of basal-like triple-negative breast carcinoma (BL-TNBC). Here, we present a study of MSC formalin-fixed paraffin embedded (FFPE) tissue specimens using novel in-depth quantitative proteomic strategy.