Desmoid tumor-associated pain is dependent on mast cell expression of cyclooxygenase-2

Background: This study aimed to investigate the expression profile of cyclooxygenase-2 (COX-2) in desmoid tumor specimens and to evaluate the correlation of intratumoral COX-2 expression with pain status. Methods: Sixteen patients with histologically proven desmoid tumors who attended our institution between 2003 and 2010 were enrolled in this study. COX-2 protein expression in desmoid tumors was determined by immunohistochemistry. COX-2 - positive cells had similar morphology to that of mast cells, and therefore, immunohistochemical staining for tryptase was performed in co-localized sections. The number of COX-2 - positive cells in 10 consecutive fields was counted at 400x magnification. Patients were stratified into 2 groups according to the number of COX-2-positive cells, the COX-2 - positive group (>= 10 COX-2 - positive cells) and the COX-2 - negative group (<10 COX-2 - positive cells). The prevalence of painful tumors was compared between the 2 groups. Results: COX-2 was expressed in 9 patients (56%). COX-2 proteins were expressed not in tumor cells but in tryptase-positive mast cells in the stroma of desmoid tumors. 6 of 9 patients in COX-2 - positive group had painful tumors. This difference was statistically significant according to the chi-squared test (p = 0.036), suggesting a positive correlation between COX-2 expression and tumor-associated pain. Conclusions: Our results indicated that COX-2 secretion from mast cells modulates desmoid tumor-associated pain. In addition, mast cells may at least in part contribute to the pathogenesis of desmoid tumors.