Salvage radiotherapy for oligo-progressive malignant pleural mesothelioma

No standard treatment option is available for patients with unresectable malignant pleural mesothelioma (MPM) progressing after upfront chemotherapy. We aimed to explore the role of focal radiotherapy (FRT) as a treatment modality for oligo-progressive MPM.In this retrospective study, consecutive patients pretreated with ≥1 lines of chemotherapy were included. Oligo-progressive MPM was defined as an unresectable disease with radiological progression at ≤3 sites according to a chest-abdominal contrast-enhanced computed tomography. Patients were treated with either stereotactic body radiotherapy (SBRT, ≥5 Gy per fraction) or hypo-fractionated radiotherapy (hypoRT,5 Gy per fraction). Time to further systemic therapy (TFST) and local control (LC) after FRT were the primary endpoints. Biologically effective dose (BED) was calculated using three different alpha/beta models (1.5 Gy, 3 Gy and 10 Gy).From April 2006 to March 2019, 37 patients were treated on 43 pleural lesions; 16/37 (43 %) had undergone upfront multimodality treatment (MMT) including surgery. FRT was given in 22/37 (59.5 %) after one line of chemotherapy. SBRT was delivered for 26/43 lesions (60.5 %), hypoRT for 17/43 (39.5 %). Median TFST was 6 months (95 % CI 4.9-7.1). LC at 6 months and 1 year was 84 % and 76 %, respectively. Median TFST was longer in patients treated after 1 vs1 line of chemotherapy (9 vs 4 months, p = 0.001) and in patients pretreated with MMT (6 vs 3 months, p = 0.021). Six-month LC was better in patients treated with a BED 100 using alpha/beta 1.5 and 3. No ≥ G3 acute or late toxicities were reported.FRT was feasible in selected patients with oligo-progressive MPM, allowing delay of further systemic therapies, with no severe toxicity. FRT was more effective when performed at progression after one line of systemic therapy. Our results suggest a radio-resistant behavior of MPM.