CD26 overexpression is associated with prolonged survival and enhanced chemosensitivity in malignant pleural mesothelioma

Purpose: Malignant pleural mesothelioma (MPM) is an aggressive and therapy-resistant neoplasm arising from the pleural mesothelial cells, without established indicators to predict responsiveness to chemotherapy. Experimental Design: Our study involving 79 MPM patients showed that 73.4% of MPM expressed CD26 on cell membrane. Results: The majority of epithelioid and biphasic types of MPM expressed CD26 on the cell membrane, whereas the sarcomatoid type showed a lack of CD26 surface expression. Although the sarcomatoid type was associated with poor prognosis (P < 0.0001), no significant relationship between CD26 expression and survival was observed. On the contrary, there was a trend for an association between response rate to chemotherapy and CD26 expression (P = 0.053), with a higher level of CD26 expression more likely to be linked to better response to chemotherapy. Moreover, CD26 expression was a significant factor associated with improved survival in patients who received chemotherapy [median survival time (MST), 18.6 vs. 10.7 months, P = 0.0083]. Furthermore, CD26 expression was significantly associated with better prognosis in patients receiving non-pemetrexed-containing regimens (MST, 14.2 vs. 7.4 months, P = 0.0042), whereas there was no significant association between CD26 expression and survival time for patients receiving pemetrexed-containing regimens. Our in vitro and microarray studies showed that mesothelioma cells expressing high CD26 displayed high proliferative activity, and CD26 expression was closely linked to cell-cycle regulation, apoptosis, and chemotherapy resistance. Conclusions: Our results strongly suggest that CD26 is a clinically significant biomarker for predicting response to chemotherapy for MPM.