Cathepsin D as a potential prognostic marker for lung adenocarcinoma

We previously identified cathepsin D as a possible marker for lung adenocarcinoma (AD). The purpose of the present study is to evaluate the correlation between cathepsin D expression and clinicopathological findings or prognosis. We conducted immunohistochemistry (IHC) to assess 150 AD tissues. For these 150 tumors, TTF-1 expression, EGFR and KRAS gene mutations, and ALK rearrangements had already been examined. Cathepsin D expression was detected in 44% (66 of 150, IHC score ≥1+) and 27.3% (41 of 150, IHC score ≥2+). Cathepsin D-positive (IHC score ≥2+) tumors were more poorly differentiated than cathepsin D-negative ones, while all lepidic predominant invasive adenocarcinomas showed no cathepsin D expression. Univariate analysis revealed a poor prognosis for cathepsin D-positive lung AD patients with an IHC score ≥2+ (P=0.044). Cathepsin D expression was more frequent in TTF-1-negative than in TTF-1-positive ADs (P=0.034), and more frequent in ADs with EGFR wild genotype than mutant EGFR (P<0.001). Regarding AD patients with ALK rearrangements, 4 were positive for Cathepsin D, while 2 were negative. Cathepsin D expression is indicated to be a possible prognostic marker for lung AD and to correlate with a more poorly differentiated form.