AIM

To compare the sensitivity and staining pattern of the new immunohistochemical antibody to tyrosinase (T311) with S-100, HMB45, and the recently evaluated antibody to melan-A (A103) in a range of melanocytic lesions.

METHOD

Archival, formalin fixed, paraffin wax embedded sections from 50 benign and malignant melanocytic lesions were stained immunohistochemically with anti-tyrosinase, A103, S-100, and HMB45. They were scored semiquantitatively for the distribution and intensity of staining.

RESULTS

All melanomas, with the exception of desmoplastic melanoma, showed some staining with all four antibodies. Overall, T311 and A103 showed an intermediate sensitivity compared with that of S-100 and HMB45. T311 stained most benign and malignant lesions strongly and diffusely with minimal background staining. Immunoreactivity was found to be patchy in some naevi, with weak or absent staining of the mature melanocytes. A103 showed strong and diffuse staining of all benign lesions and most melanomas with minimal background staining. S-100 was the most sensitive, with diffuse staining of most lesions, including desmoplastic and metastatic melanoma, but lacked specificity. HMB45 was the least sensitive antibody, frequently demonstrating patchy staining with absent staining in some benign naevi.

CONCLUSIONS

S-100 remains the most sensitive marker of melanocytes. However, because of its lack of specificity, it should be used with at least one other more specific antibody. HMB45 is more specific, but lacks sensitivity; T311 is a reliable marker of melanocytes in paraffin wax embedded sections and is worth consideration for use in a staining panel, although it shows no additional benefit over A103.