Trophoblast Cell-surface Antigen 2 Expression in Advanced Lung Cancer Patients and the Effects of Anti-cancer Treatments

Trophoblast cell-surface antigen 2 (TROP2) is expressed on the surface of trophoblast cells and many malignant tumor cells. However, data on TROP2 expression in advanced lung cancer are insufficient, and its changes have not been fully evaluated. We assessed the prevalence and changes in TROP2 expression in patients with lung cancer who received anti-cancer treatments using immunohistochemical (IHC) analysis with an anti-TROP2 antibody (clone: SP295). IHC scores were graded from 0 to 3; grade ≥ 2 was considered positive for TROP2 expression. We defined a difference in IHC score, before and after anti-cancer treatments, as the change in TROP2 expression. Before anti-cancer treatment, TROP2 expression was observed in 89% (143/160) of the patients and was significantly more common in adenocarcinoma and squamous cell carcinoma than in neuroendocrine carcinoma (P < 0.001). After anti-cancer treatment, TROP2 expression was observed in 87% (139/160) of the patients. The distribution of TROP2 expression in post-treatment samples was analogous to that in pre-treatment samples when compared using the Wilcoxon signed-rank test (P = 0.509). However, an increase in TROP2 expression was seen in 19 (12%), and a decrease in 20 (13%) patients. Patients treated with targeted therapy showed significantly higher changes in TROP2 expression (P = 0.019) and thoracic radiotherapy was more likely to increase TROP2 expression than chemotherapy alone. Although some anti-cancer treatments might alter the TROP2 expression, TROP2 was expressed in most lung cancer specimens before and after anti-cancer treatments. These results support the development of TROP2-directed therapy against advanced lung cancer in various treatment lines.