[101] Comparing the Intrinsic Tumor Subtype of Invasive and In-Situ Components of Breast Carcinoma: Analysis of 34 Tumors Using the PAM50 RT-PCR Assay.

Natalie Banet, Charles M Perou, Katherine A Hoadley, Philip S Bernard, Chad Livasy. University of North Carolina, Chapel Hill; Carolinas Medical Center, Charlotte, NC; University of Utah, Salt Lake City

Background: The PAM50 is a multigene RT-PCR assay used to identify the intrinsic subtype of breast carcinomas. Intrinsic subtypes have been identified in both invasive and in-situ carcinomas. Comparing the gene expression profiles of the invasive and in-situ components of breast carcinomas may improve our understanding of breast cancer evolution and have implications for interpreting multigene assay results. The aim of this study is to compare the tumor subtype of matched invasive and in-situ components of breast carcinomas.
Design: A heterogeneous group of 43 invasive breast carcinomas, each containing an in-situ component, was selected from our files. Tumor rich 1 mm cores taken from both the invasive and in-situ components of tumors underwent qRT-PCR and PAM50 subtyping. Intrinsic subtype and quantitative ER and HER2 expression levels for corresponding in-situ and invasive components were compared.
Results: Nine cases were excluded due to identification of a normal-like subtype. Results of the remaining 34 cases are summarized below.

 INV LUM AINV LUM BINV BASAL-LIKEINV HER2-ENRICHED
DCIS LUM A9102
DCIS LUM B0400
DCIS BASAL-LIKE0172
DCIS HER2-ENRICHED1205


25 of 34 (73%) of cases showed the same intrinsic subtype in both the invasive and in-situ components. All invasive basal-like carcinomas (7/7) were associated with basal-like DCIS. 9 cases (27%) demonstrated a different intrinsic tumor subtype between the invasive and in-situ components. These cases also demonstrated significant differences in quantitative ER and/or HER2 expression levels between the invasive and in-situ components.
Conclusions: The intrinsic tumor subtype of the in-situ and invasive components of most breast carcinomas is the same. A significant minority of cases (27%) demonstrated differences in tumor subtype and quantitative ER and/or HER2 expression levels between the in-situ and invasive components indicative of intra-tumoral heterogeneity. These findings suggest that multigene assay results from whole sections of invasive carcinoma could be altered by contaminating DCIS with a significantly different gene expression profile. It may be important to microdissect invasive tumors containing a high percentage of DCIS before analysis.
Category: Breast

Tuesday, March 1, 2011 1:00 PM

Poster Session IV # 9, Tuesday Afternoon

 

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