Background Several reports have shown expression of cyclooxygenase-2 (COX-2) in malignant skin tumors. COX-2 has also recently been reported as a marker of malignant melanoma (MM).
Objective Our aim was to investigate whether there is a difference in the immunohistochemical expression of COX-2 between malignant and benign melanocytic lesions of the skin.
Methods We selected 40 archival cases of MM including 10 cases of superficial spreading melanoma, 10 of lentigo maligna melanoma, 10 of nodular melanoma, and 10 of acral lentiginous melanoma. For comparison, we also selected 35 benign melanocytic lesions, which included 15 nonatypical nevi and 10 atypical nevi. The remaining 10 cases were Spitz nevi. COX-2 immunohistochemical staining was performed, and intensities were assessed quantitatively.
Results The MM group and the benign melanocytic nevi group showed a highly statistically significant difference in the intensity of COX-2 expression (P < 0.0001). Staining intensity in the dermal component of MM cases also showed a tendency to increase with increasing tumor depth. By contrast, the intensity of the dermal component in the melanocytic nevi group decreased with increasing depth as the nevus cells matured from type A to type C cells. No statistical difference was noted between the MM and Spitz nevi cases (P = 0.20).
Conclusions Malignant melanoma shows stronger immunohistochemical expression of COX-2 than benign melanocytic nevi. Although COX-2 cannot be used alone to differentiate MM from melanocytic nevi, it may serve as an aid in the differential diagnosis of melanocytic skin lesions.