PTGS2 and melanoma: We have demonstrated that the COX-2 protein is strongly expressed in the majority of primary malignant melanomas and is related to the number of mitoses (P<0.001), tumor thickness (based on the Clark level and Breslow) (P<0.001), melanoma subtypes (0.01), lymph node involvement (P<0.001) and metastases (P<0.001).