Expression of Gamma-Laminin, Cytokeratin 5 and Cytokeratin 5/6 in Metaplastic and Basal-like Breast Carcinomas
SM O'Connor, L Niemeier, R Bhargava, WT Parks, DJ Dabbs. UPMC Magee-Womens Hospital, Pittsburgh, PA
Background: Basal-like (BL) and metaplastic (MPC) breast carcinomas are part of the triple-negative (TN) group of breast carcinomas. The triple-negative status connotes negativity for estrogen and progesterone receptors and HER2 oncoprotein. Identification of the basal phenotype in TN tumor requires the demonstration of cytokeratin (CK) 5/6 and/or epidermal growth factor receptor (EGFR). A recent paper has described the superiority of gamma-laminin over CK 5/6 in the identification of BL and MPC. We have recently demonstrated the dramatic superiority of CK 5 over CK 5/6 for identification of BL tumors (Mod Pathol 2008;21 [suppl 1]:23A-Abstract 92). This study compares the efficiencies of CK 5/6, CK 5 and gamma-laminin to identify BL and MPC.
Design: Nine MPC carcinomas (previously positive for 2 of the following 4 markers: CK 5/6, CK 14, CK 17, EGFR) and 14 BL were used as a basis for this study. All tumors were immunostained with CK 5/6 (D5 and 16B4, Ventana Medical Systems), CK 5 (XM26, Vision Biosystems), EGFR (3C6, Ventana Medical Systems) and gamma-laminin (D4B5, Chemicon International). EGFR was scored analogous to current HER2 guidelines. Other antibodies were scored numerically based on the percent of cells stained: 1= 1-25%; 2=26-50%; 3= 51-75%; 4 >75%.
Results: All BL and MPC were CK 5/6, CK 5, and EGFR positive. All CK 5 positive cases had more than 75% cells positive (score=4) diffusely. Immunostaining for CK 5/6 was extremely variable, with less than half of the cases demonstrating a score of at least 3, and only 5 scoring a 4. Gamma-laminin immunostaining, similar to CK 5/6, was quite variable, with only 7 cases scoring a 4.
Expression of Gamma-Laminin, CK 5, and CK 5/6.
Conclusions: Cytokeratin 5 is superior to gamma-laminin and CK 5/6 for identification of the BL and MPC phenotypes of TN tumors. The intensity and percent of cells immunostaining for CK5 is substantially greater compared to laminin and CK 5/6. Basal phenotype markers are useful in identifying MPC.
Tuesday, March 10, 2009 1:00 PM
Poster Session IV # 32, Tuesday Afternoon