Asbestos Lung Burden Does Not Predict Survival in Malignant Pleural Mesothelioma: A Necropsy-Based Study of 185 Cases.

INTRODUCTION: Malignant pleural mesothelioma is an asbestos-related disease with poor survival. The prognostic role of histologic subtype is well established. Some studies (without a biological hypothesis) suggested that higher asbestos lung burden is associated with reduced survival. METHODS: We selected subjects from two series of necropsies: residents in Brescia province (North-West Italy) and workers (or persons living with them) employed in the Monfalcone shipyards (North-East Italy). Asbestos fibers and asbestos bodies in lung samples were counted using a scanning electron and an optical microscope, respectively. Separately in the two series, we analyzed median survival time and fitted multivariable Cox regression models (adjusted for sex, period and age at diagnosis, and histopatholocical diagnosis) to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for three levels of asbestos fiber counts (reference: <1 million fibers/g of dry lung tissue). RESULTS: We analyzed 185 necropsies, 83 in Brescia and 102 in Monfalcone. Despite a much higher lung burden in Monfalcone patients, median survival was slightly shorter in Brescia (8.3 mo) than in Monfalcone (10.2 mo). In Brescia, medium (1.0-9.9) and high (10+) fiber burden HRs were 0.91 (95% CI: 0.54-1.53) and 1.23 (95% CI: 0.41-3.70), respectively. In Monfalcone, the corresponding HRs were 1.18 (95% CI: 0.59-2.35) and 1.63 (95% CI: 0.77-3.45), respectively. CONCLUSIONS: No relationship between asbestos lung burden and survival was found. Histologic subtype was the strongest prognostic determinant.