The morphologic feature of mucus leakage appearing in low papillary carcinoma of the breast.

This report summarizes the clinicopathologic findings in 11 cases of low papillary carcinoma of the breast accompanied by the morphologic feature of mucus leakage into the mammary stroma. These cases were characterized by two morphologic findings. First, abundant mucus produced by the tumor cells filled the intraductal spaces where neoplastic epithelium formed very low papillary projections, ie, a feature of mucinous-producing low papillary carcinoma in situ. Second, there was expansive leakage of mucus into the mammary stroma occasionally accompanied by a few epithelial cells. All the cases showed a high level of mucus production and contained no elements of invasive ductal carcinoma or ordinary invasive mucinous carcinoma. These cases have no evidence of direct invasion of the mammary stroma by malignant cells. The average age of the 11 patients was 41 years. Foci of microcalcification were seen in some tumors (seven cases; 64%). There were no cases with lymph node metastases. All the patients underwent mastectomy with no adjuvant therapy, and they are currently alive and well.