['lizbeth]

Association of basal marker expression with outcome and trastuzumab resistance in HER2-positive breast cancer.



Abstract:

Background: Herceptin resistance is a significant challenge in the treatment of Her2-positive (Her2+) breast cancer. A subset of Her2+ breast cancers are known to express basal genes (basal Her2). We investigated the effect of basal gene expression on cell viability and Herceptin response in Her2+ breast cancer cell lines and on prognosis in patients with Her2+ breast cancer who received Herceptin. Methods: We selected 4 cell lines to represent basal Her2 (HCC1569, HCC1954) and non-basal Her2 (BT474, SKBR3) breast cancer based on their basal gene signature in microarray analysis, and treated each with vehicle, Herceptin (H), Paclitaxel (P), and H + P. Cell viability was assessed by MTT assays. Her2 pathway suppression was compared between groups using immunoblotting with anti-Her2, p-AKT, p-ERK antibodies. Expression of CK5/6, CK14, and EGFR was evaluated after immunohistochemical staining in paraffin-embedded tissue of 88 patients with Stage 1-3 Her2+ breast cancer treated with chemotherapy and Herceptin. Groups with and without basal gene expression were compared with respect to clinicopathologic parameters and survival. Results: All cell lines expressed similar levels of Her2. Both H and P alone inhibited proliferation of non-basal cell lines, and H + P had an additive cytotoxic effect. Basal cells were resistant to H, P inhibited proliferation, but H + P had no additive cytotoxic effect on cell growth in basal cells. Immunoblotting showed a significant decrease in p-Akt levels after treatment with H or H + P in non-basal cells but not in basal cells. No alterations were observed in p-ERK levels in the 4 cell lines when treated with H and H + P. Of the Her2+ patients, 33/88 (37.5%) expressed at least one basal gene. Basal Her2 tumors were associated with higher grade (p=0.04) and more ER/PR-negativity (p<0.01). CK14 expression correlated with worse overall survival by log-rank test (p=0.02), while EGFR showed a similar trend (p=0.06). Conclusions: Basal Her2 cell lines are resistant to Herceptin. This resistance is associated with Herceptin refractory PI3K/Akt activity. CK14 expression is predictive of worse prognosis in Her2+ breast cancer patients treated with Herceptin.