Efficacy of Immunotherapy Versus Chemotherapy in Advanced Pleural Mesothelioma: A Turkish Oncology Group (TOG) Study.

Background and Objectives: This study aimed to evaluate the effectiveness of immunotherapy compared to chemotherapy across different treatment lines in patients with pleural mesothelioma. It also sought to identify factors influencing the success of immunotherapy, such as histological subtype, PD-L1 expression, type of asbestos exposure, and metastatic status. Materials and Methods: A retrospective analysis was conducted with 60 patients diagnosed with pleural mesothelioma. Data on age, gender, histological subtype, and asbestos exposure were collected for all patients and PD-L1 expression was assessed in a subset of patients. Patients received either chemotherapy or immunotherapy as first-, second-, and third-line treatments, and progression-free survival (PFS) and treatment responses were evaluated. Results: Among the 60 patients, 35 (58.3%) were male and the median age was 59 years. The majority (71.7%) had epithelioid histology and 28.3% had distant metastases. Asbestos exposure was documented in 65% of the cases. PD-L1 expression of ≥1% was found in 13 of 17 patients tested. First-line treatments included immunotherapy for 11 patients and chemotherapy for the others, with immunotherapy achieving median PFS of 9 months versus 6 months for chemotherapy, although the difference was not statistically significant. In third-line treatments, immunotherapy significantly outperformed chemotherapy with median PFS of 6 months compared to 3 months (p = 0.048). Absence of metastasis and prior asbestos exposure in an endemic region were linked to better immunotherapy outcomes. Conclusion: Immunotherapy shows increased efficacy in later treatment lines for pleural mesothelioma, especially for patients without metastases or with prior endemic asbestos exposure. Tailored therapeutic strategies should be further explored in prospective studies.