[130] Basal-Like Ductal Carcinoma In Situ Is a Precursor Lesion for Invasive Metaplastic Breast Carcinoma

DA Budwit, CM Perou, CA Livasy. University of North Carolina, Chapel Hill, NC

Background: Metaplastic breast carcinoma (MBC) is an uncommon variant of breast cancer that typically demonstrates a triple-negative phenotype (ER-, PR-, HER2-). Multiple studies have documented the presence of an in situ counterpart of basal-like breast carcinoma. Detailed studies characterizing the precursor lesions of invasive MBC are lacking. The aim of this study was to evaluate the histopathology and immunophenotype of ductal carcinoma in situ (DCIS) associated with MBC and to determine whether the DCIS demonstrates a basal-like phenotype.
Design: Review of UNC surgical pathology files from 1997 to 2008 revealed 20 cases of MBC with accessible slides and blocks. Complete histopathologic review of these cases was performed to document histopathologic features of the invasive and, if present, in situ components including nuclear grade, presence of necrosis, and presence/type of metaplastic features. Immunohistochemistry (IHC) for ER, HER2, EGFR and cytokeratin (CK) 5/6 was performed on all cases with an in situ component. Basal-like tumors were defined as those showing an ER-, HER2-, and CK5/6+ and/or EGFR+ immunophenotype.
Results: A total of 9 of 20 cases demonstrated an in situ component associated with the invasive MBC. The histologic differentiation of the invasive component in these 9 cases included 5 squamous, 2 squamous and sarcomatoid, 1 chondroid, and 1 chondroid and sarcomatoid carcinomas. The associated DCIS was high nuclear grade 3 with necrosis in all 9 cases. The DCIS foci did not show associated metaplastic changes in 8 of 9 cases. One of the 9 cases showed focal squamoid differentiation within the DCIS. Extent of DCIS ranged from rare foci (<1%) to extensive (>75%) of total tumor volume. All nine cases exhibited a basal-like phenotype in the invasive component. Immunohistochemical results for all four markers were able to be interpreted for the DCIS component in 7 of 9 cases. All 7 cases demonstrated a basal-like DCIS phenotype, each showing an ER-, HER2-, CK5/6+ and EGFR+ phenotype.
Conclusions: Basal-like DCIS is associated with MBC and is a likely precursor lesion for this rare subtype of invasive carcinoma. DCIS associated with MBC is typically high-grade and often lacks the characteristic metaplastic changes seen in the associated invasive component. Identification of metaplastic changes within expansive DCIS in biopsy specimens should raise the suspicion for the presence of invasive carcinoma.
Category: Breast

Monday, March 9, 2009 11:45 AM

Platform Session: Section B, Monday Morning