S47 Impact of number of sampling sites and specimen dimension on the performance of nuclear grade and growth patterns in predicting survival in epithelioid malignant pleural mesothelioma: a single institution review of 614 cases

Introduction There is limited evidence regarding the optimal number of sampling sites and specimen dimension in histological diagnosis of malignant pleural mesothelioma (MPM). Previously we have validated 2-tier nuclear grade as an independent predictor of survival in epithelioid MPM. This study evaluates the association between sampling parameters and the performance of 2-tier nuclear grade and growth pattern as survival predictors using a biopsy-heavy cohort. Methods Clinicopathological information including the number of sampling sites, tissue dimension, 2-tier nuclear grade, predominant growth pattern and overall survival (OS) were retrieved from an institutional mesothelioma database comprising 614 consecutive cases of epithelioid MPM over a 15 year period. Survival analysis was performed using Kaplan-Meier method. Association between categorical variables was analysed using Fisher exact test, and was assessed in relation to biopsy size and number. Statistical significance was defined as p Results The mean age was 69.1 years, with male preponderance (75.6%). 87.0% (534/614) received biopsy only. The median number of sites sampled was 1 (range 1–20). The median maximum tissue dimension was 18 mm for biopsies (range 2–140 mm) and 145 mm for resections (range 40–350 mm). 17.7% of all biopsies (95/534) were taken from a single site with a maximum dimension of ≤10 mm (median: 8 mm). Low grade tumours showed significantly prolonged OS compared with high grade (19.3 months vs. 8.9 months, p Conclusions We propose an optimal sampling standard of 3 sites or a maximum tissue dimension of ≥20 mm from a single site. This then allows a 2-tier nuclear grading system to provide prognostic stratification for clinical care and research of epithelioid MPM.