Objective: To investigate the expression of promyelocytic leukaemia (PML) protein in lung carcinomas and the clinical significance thereof.
Methods: A tumor tissue microarray with lung samples from 148 patients with lung carcinoma and 5 patients with pulmonary benign tumor, and 7 patients with other benign diseases resected during operation. The cases with at least triplicate 0.6-mm cores per tumor or tissue were analyzed. Immunohistochemistry (SP method) was used to detect the expression of PML protein. The association between PML expression and post-operational survival was evaluated.
Results: Four cases of lung carcinoma were excluded because their available cores were less than 3. The remaining 144 lung carcinoma cases included 45 cases with squamous cell carcinoma, 62 with adenocarcinoma, 23 with small cell lung carcinoma (SCLC), 7 with large cell carcinoma, 5 with pleomorphic carcinoma, 1 with carcinoid, and 1 with adenosquamous carcinoma. Forty of the 144 cases were PML protein positive in the nucleus, 26 were PML protein positive in the cytoplasm, and 12 were PML protein positive in both the nucleus and cytoplasm. Among the 5 cases with benign lung tumors, two cases with pulmonary leiomyomas had strong expression of PML. Among the 7 normal pulmonary tissues, one case with bronchial mucosa had a moderate expression of PML on the nuclei in the basilar part, and the 6 cases with normal alveolar epithelium did not express PML. The rates of PML expression on cell nuclei were 31.4% and 8.7% respectively in the non-small cell lung carcinoma (NSCLC) and SCLC samples (chi(2) = 4.968, P = 0.026). Farish, but not strong, expression on cytoplasm was found in 39.1% cases of SCLC and in 14% cases of NSCLC (chi(2) = 6.609, P = 0.010). PML protein was found in 9 patients with SCLC, but absent in the other 14 cases. The 5-year cumulative survival rate of the PML positive SCLC patients was 50%, significantly higher than that of the PML-negative SCLC patients (23%, chi(2) = 3.931, P = 0.047). Lack of PML protein (RR = 0.127, 95% CI = [0.027, 0.592]) and senior pathologic TNM stage (RR = 3.148, 95% CI = [1.029, 9.631]) were two hazardous factors that influenced long-term survival of postoperative SCLC patients.
Conclusion: As an important suppressor of tumor, PML may be a useful indicator to predict postoperative prognosis in patients with SCLC.