P36. The prognostic potential of circulating and tissue activin A level in malignant pleural mesothelioma

Background: Malignant pleural mesothelioma (MPM) is an aggressive malignancy characterized by poor outcome and there is a lack of prognostic biomarkers to estimate prognosis. Previously we have shown that suppression of activin A can interfere with MPM tumor growth. In the current study, we compare the circulating and tissue expression level of activin A as a prognostic biomarker in MPM.

Methods: In a cohort of 53 MPM patients, plasma samples were collected between 2010 and 2014. Controls consisted of age-matched healthy individuals (n=46) and patients with pleuritis or pleural fibrosis (n=16). Circulating activin A was measured by ELISA and correlated to clinicopathological data. Furthermore, activin A expression in the tumor tissue was semiquantitatively measured by immunohistochemistry in 24 patients.

Results: Plasma activin A level was significantly elevated in MPM patients (n=53, 843±122 pg/mL) when compared to healthy controls (452±144 pg/mL, P=0.0039). Non-malignant pleuritis or pleural fibrosis patients only showed a modest, non-significant increase (625±95 pg/mL, P=0.093). Circulating activin A levels were slightly increased in cases with non-epitheloid morphology (n=16, 1101±183) when compared to epithelioid (n=37, 732±153 pg/mL, P=0.13). MPM patients with below median activin A concentrations had a modestly and non-significantly longer overall survival when compared to the high activin A level patients (469 vs. 271 days, P=0.4751). Interestingly, there was no correlation between circulating and tissue expression level of activin A in 17 patients where both parameters could have been analyzed.

Conclusions: Our findings suggest that the measurement of circulating activin A may support the diagnosis and prognosis of MPM but additional patient cohorts need to be analyzed to establish the diagnostic and prognostic value of this non-invasive biomarker.

Keywords: Mesothelioma; activin A