Background: Primary mucosal melanomas (MMs) of the head and neck are a rare entity. Melanomas with characteristic melanin-pigmented tumor cells are easy to diagnose, but those without melanin-pigmented tumor cells, amelanotic melanomas, are difficult to identify and need immunohistochemistry (IHC) to confirm the final diagnosis. In this study, we examined the expression of three melanocytic differentiation markers, HMB-45, S-100, and Melan-A in primary oral and nasal MMs. We tried to evaluate whether HMB-45, S-100, and Melan-A were useful for diagnosis of primary oral and nasal MMs and to find out which marker was the best of the three.
Methods: This study used IHC to examine the expression of HMB-45, S-100, and Melan-A in 17 formalin-fixed paraffin-embedded specimens of primary oral and nasal MMs. The staining intensities (SIs) and labeling indices (LIs) of HMB-45, S-100, and Melan-A in 17 MMs were calculated and compared between any two markers.
Results: Immunostaining results showed that the positive rate was 94% (16 of 17) for HMB-45, 88% (15 of 17) for S-100, and 71% (12 of 17) for Melan-A in 17 MMs. The SI of HMB-45 was significantly higher than that of S-100 (P = 0.0011) or of Melan-A (P = 0.0034). In addition, the mean LI of Melan-A (59 +/- 43%) was significantly lower than that of HMB-45 (83 +/- 28%, P = 0.0065) or of S-100 (79 +/- 33%, P = 0.0237).
Conclusions: Our results indicate that both HMB-45 and S-100 show a high positive rate and LI in MMs and therefore may be good markers for immunohistochemical diagnosis of primary oral and nasal MMs. In addition, HMB-45 may be a more sensitive marker than S-100 because HMB-45 shows a significantly higher SI than S-100 in this study.