Tryptase Mast Cells in Malignant Pleural Mesothelioma as an Independent Favorable Prognostic Factor

IntroductionMalignant pleural mesothelioma is a highly aggressive neoplasm with an incidence that is increasing world-wide. Mast cells are part of the innate immune system and have been associated with different solid tumors, but there is controversy surrounding their pro- and antitumorigenic effects in cancers. There are two subsets of human mast cells, resulting from the expression of different enzymes: tryptase positive mast cells and chymase positive mast cells. The purpose of this study was to determine the presence and prognostic significance of tumor infiltrating mast cells in mesothelioma.MethodsTryptase and chymase mast cell counts were determined by immunohistochemistry in 60 patients with mesothelioma. All pathologic samples were from patients who underwent treatment with intrapleural preoperative interleukin-2 (18 × 106 IU/d for 3 days). After one day of recovery, patients underwent surgery. Pleural samples were also immunostained for CD34 to evaluate microvessel count.ResultsHigh tryptase mast cells counts were found in the majority (73.3%) of the cases studied, and the results were significantly associated with both overall survival (p = 0.02) and time to progression (p = 0.01). This finding was confirmed using multivariate analysis: a higher tryptase mast cells count emerged as an independent favorable prognostic factor (p = 0.02). However, tryptase mast cells count did not show significant correlation with microvessel count.ConclusionsThese results suggest that tumor infiltrating tryptase mast cells, after interleukin-2 preoperative induction therapy, predict improved clinical outcome in patients with malignant pleural mesothelioma, and highlight the critical role of the local inflammatory response in mesothelioma cancer progression.