Differential immunoreactivity of melanocytic lesions of the conjunctiva

Aims: To evaluate the expression of S100NKI/C3 and HMB45 antigens in melano cytic lesions of the conjunctiva and the ability of HMB45 to aid assessment of neoplasia. Methods and results: Stored formalin-fixed specimens of conjunctival melano mas and primary acquired melanosis were considered as participants and conj unctival naevi and racial melanosis as controls. Ninety-seven conjunctival melanocytic lesions were analysed using formalin-fixed paraffin-embedded ma terial. These included 20 melanomas arising in the context of primary acqui red melanosis (PAM), 22 melanomas arising without evidence of pre-existing PAM, seven cases of PAM with atypia, nine cases of PAM with no atypia, 35 c onjunctival naevi and four cases of racial melanosis. S100 and NKI/C3 were similarly expressed in all lesions, with at least one of these markers posi tive in 100%, of the lesions examined. HMB45 was expressed in 72.7% of prim ary melanomas and 85% of melanomas in the context of PAM: 42.8%, of PAM wit h atypia expressed HMB45 while it was expressed in 11.1% of PAM without aty pia and 8.5% of naevi. Racial melanosis cases did not express HMB45. S100 a nd NKI/C3 were expressed to a similar extent in all groups. Conclusions: S100 and NKI/C3 are useful markers to assess the extent of mel anocytic lesions in the conjunctiva. HMB45 immunoreactivity can act as a us eful aid to histopathology for the distinction of benign from malignant con junctival lesions. particularly in the context of primary acquired melanosi s.