[188] Primary Mucinous Carcinoma (MC) of Breast – A Proposal of Precursor Lesion & Possible Tumor Progression

Oleksandr N Kryvenko, Dhananjay A Chitale, Jiyoon Yonn, Javier Arias-Stella, Min W Lee. Henry Ford Hospital, Detroit

Background: MC is a rare primary tumor of the breast associated with a relative favorable outcome. Data in the literature are limited regarding the precursors of MC & tumor progression unlike invasive ductal carcinoma,NOS (IDC-NOS). In this study we sought to characterize association of mucinous ductal carcinoma in situ (DCIS) with MC as a precursor lesion.
Design: Study included 128 cases of MC over a 10 year period. Based on published criteria, tumors were further classified based on cellularity & extracellular mucin content:Type A MC (paucicellular, 60-90% extracellular mucin in >90%of tumor) & Type B-MC (cellular,<60% extracellular mucin in >90% of tumor). IDC-NOS with minor mucinous component were subtyped as mixed MC. All slides were reviewed to identify DCIS, with focus on transitional pattern between the MC & DCIS. Immunohistochemistry (IHC) for p63 & calponin was done to assess presence of myoepithelial cells in the transitional areas.
Results: There were 70 Type A MC & 39 Type B MC & 19 cases of mixed MC. 15 specimens were needle core biopsy, the rest excisions. Associated DCIS was identified in 88 (69%) cases (5 biopsies & 83 excisions: Type A MC - 46; Type B MC – 29; mixed MC – 13) with 81 cases showing luminal expansion by mucin. 59 of 81 DCIS (73%) with luminal mucinous distension revealed transitional pattern between DCIS & MC. The predominant pattern of DCIS was cribriform & solid (65/81)with luminal mucinous distention, focal flattening & attenuation of the epithelium, disruption of the epithelium with mucocele like extravasation of mucin with detached floating papillae. Detached papillae in the mucin pool were confirmed by presence of peripheral apocrine snouts & were negative for p63 & calponin. Gradual disappearance of myoepithelial cells in transition was confirmed by IHC in 21/43 stained cases. Solid DCIS was associated with aggressive MC phenotypes (mixed MC & Type B MC).

Conclusions: MC has distinct mucinous DCIS precursor with characteristic transition zone. Pathogenesis of MC may involve mucinous overdistention of ducts involved by DCIS with rupture & extravasation of malignant epithelium.We believe Type A MC & Type B MC represent spectrum of tumor progression as Type A MC gradually deplete extracellular mucin becoming Type B MC & ultimately non mucinous IDC.
Category: Breast

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 23, Wednesday Afternoon


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