Abstract
Background : Pure mucinous carcinoma (PMC), micropapillary variant, is an unusual form of invasive breast cancer exhibiting dual mucinous and micropapillary differentiation. This variant is considered to be aggressive because of the high rate of lymphatic permeation and nodal metastasis. Morphologically, the neoplastic cells form a micropapillary architecture, as seen in invasive micropapillary carcinoma, and float in lakes of mucin. Herein, we describe the cytologic and histologic findings of a case of PMC of the breast, micropapillary variant.
Case : A 44-year-old woman presented with a 2-cm diameter mass in her right breast. Fine needle aspiration cytology showed numerous neoplastic cells forming a micropapillary pattern with hobnail and tubular-like features, against a mucinous background. Pathological examination of the mastectomy specimen showed neoplastic cells forming diffuse micropapillary nests against a mucinous stroma. These nests were demonstrated by MUC1 immunohistochemical staining to show the characteristic inside-out pattern of micropapillary carcinoma. Therefore, a diagnosis of PMC, micropapillary variant, was made. No lymphatic permeation or axillary lymph node metastasis was observed.
Conclusion : Micropapillary clusters with hobnail and tubular-like features against a mucinous background are diagnostic clues for PMC, micropapillary variant.
