LAUSR

308 Androgen Receptor Expression Is Higher in CK5/6 Negative versus CK5/6 Positive Triple-Negative Breast Cancers Tao Zuo, Ali Cicek, Olivia L Snir, Yuanxin Liang, Malini Harigopal. Yale School of Medicine, New Haven, CT; Tufts Medical Center, Boston, MA. Background: Androgen receptor (AR) expression is observed in about 25% to 75% of triple-negative breast cancers (TNBCs). However the degree of AR expression in TNBC varies widely depending on the cancer subtypes, cutoff for positivity and assay methodology. Design: TMAs with 291 TNBCs of which 228 were available for immunohistochemical study for AR and CK5/6 expression. The percentage and intensity of both markers were evaluated by two pathologists independently. Results: The Pearson correlation between two pathologists for AR score was R2=0.94, CK5/6 positive (+) cases (R2=0.89), and CK5/6 negative (-) cases (R2=0.9595). AR expression in TNBCs using 1% and 10% cutoff was 41% and 28% respectively of all TNBCs. CK5/6 expression was seen in 122 of 228 (54%), 106 of 228 (46%) TNBCs. Within AR positive TNBCs using 1% cutoff, in CK5/6+ and CK5/6groups (56 AR+/ CK5/6and 34 AR+/CK5/6+) there was no statistically significant difference (p = 0.207). Within AR positive TNBCs using 10% cutoff, in CK5/6+ and CK5/6groups (43 AR+/CK5/6and 20 AR+/CK5/6+) there was statistically significant difference (p= 0.0247). The percentage and intensity of AR expression in CK5/6 negative cases was higher compared with CK5/6 positive cases (p= 0.0036, p= 0.0325) respectively.