Abstract Book - Pathology and Laboratory Medicine - University of ...

ABSTRACT #2CLINICAL SCIENCESRESIDENTORAL presentationLineage-specific markers are rarely expressed in basal-like breast cancerJoyce M Leo 1 , Jennifer Choo 1 , Allen M Gown 1,2 , Torsten O Nielsen 1 , C Blake Gilks 11University of British Columbia, Department of Pathology, Vancouver, Canada; 2 PhenopathLaboratories, Seattle, WA, United StatesBackground /objectivesBasal-like breast cancer is defined by expression profiling, and is an aggressive subtype accounting forapproximately 15% of breast cancer cases and a disproportionately high percentage of breast cancer metastases(particularly to lung and brain) and deaths. Basal-like breast cancers rarely express the common breast cancerbiomarkers estrogen receptor, progesterone receptor and HER-2. In this study we sought to characterize theirexpression of other commonly-used diagnostic immunomarkers of carcinoma cell lineage, based on the hypothesisthat they will be more likely to show aberrant expression of lineage-specific markers (i.e. decreased expression ofbreast cancer markers and increased expression of markers of non-breast lineage).14MethodsBasal-like breast cancers, defined by PAM50 expression profiling, were placed in a tissue microarray andimmunostained for mammaglobin, GCDFP-15, WT1, TTF1, CDX2, napsin A, PAX2, PAX5 and PAX8.ResultsTTF1, WT1, CDX2 and napsin A were negative in all cases. Among commonly used markers of the breastlineage, mammaglobin was positive in only 2/46 and GCDFP-15 was positive in just 1/46 of the basal-like breastcancers tested. PAX2 and PAX5 were positive in 1/46, while PAX8 was positive in 2/46 cases of basal-like breastcarcinomas.ConclusionsBasal-like breast cancers show a very low frequency of expression of the breast cancer markers mammaglobin andGCDFP-15, limiting their usefulness as markers of site of origin when one is examining metastatic carcinomaof unknown primary and metastatic basal-like breast cancer is a consideration. Basal-like carcinomas only rarelyexpress antigens used as markers of non-breast origin, such as WT1, TTF1, CDX2, napsin A, PAX2, PAX5 andPAX8. Better positive markers are needed for identification of basal-like breast cancer in the metastatic setting.2012 * Oral/Poster Presentations