Platelet counts (PLT) at baseline and on treatment as predictor for progression free survival (PFS) in patients with advanced malignant pleural mesothelioma (MPM): EORTC 08052 study.

Abstract

7585 Background: PLT values at baseline are considered as a negative prognostic factor in several different tumor types (lung, colorectal, renal and endometrial cancer) in both early and advanced disease settings. This is an exploratory analysis of PLT (baseline and changes during treatment) and their value in predicting PFS and overall survival (OS) in patients with stage IV MPM treated with cisplatin/bortezomib in the context of a single-arm phase II trial (EORTC 08052). Methods: Patients participating in the clinical trial were chemo-naïve with histological proven MPM and PS 0/1 (cisplatin 75 mg/m2 d1 and bortezomib 1.3 mg/m2 on d1, 4, 8, 11 q3wks). PLT analysis was pre-planned in the protocol and was recorded at baseline and at each cycle. Nadir of change in PLT was recorded at 8 and 18 weeks according to predefined cut off points (median PLT value). The association of the PLT with PFS and OS was analyzed. Results: 82 patients from EORTC-08052 study were analyzed with 1394 records of PLT. The cut off point for baseline was median PLT 374x103/mm3. We confirmed that patients with baseline PLT less than median had longer PFS compared to patients with counts higher than median (median PFS: 5.7 vs. 3.7 months [mo]; HR: 0.55; 95% CI: 0.34-0.88; p: 0.012). There was also a trend towards higher OS for patients with baseline PLT values less than median (median OS: 14.8 vs.10.6 mo; HR: 0.62; 95% CI: 0.38-1.02; p: 0.059). The median decrease of PLT values at 8 wks of treatment was 243 x103/mm3. Patients with decrease lower than median had higher PFS (median PFS: 7.5 vs. 5.7 mo; HR: 2.2; 95% CI: 1.3-3.8; p: 0.003) and a trend towards higher OS (median OS: 14.9 vs. 10.6 mo; HR: 1.6; 95% CI 1-2.7; p: 0.06). Changes at 18 weeks had no prognostic value. Conclusions: Besides low baseline PLT values we observed that a decrease in PLT at 8 weeks (but not 18 weeks) during treatment could predict PFS and to less extent OS. Validation of this observation is planned.