Tyrosinase, the rate-limiting enzyme in melanin synthesis, is a melanoma associated antigen that is recognized by both CD4+ and CD8+ T-cells in an HLA-restricted fashion. Peptides derived from the tyrosinase antigen currently are being utilized as a target for T-cells in several immunotherapy protocols for metastatic malignant melanoma (MMM) at the National Institutes of Health/National Cancer Institute. Serial fine-needle aspirations of metastatic lesions are performed to monitor the antigen expression of tyrosinase during treatment by immunostaining cytologic preparations with the monoclonal antibody T311.
In the current study, 62 samples of MMM were evaluated for tyrosinase immunoreactivity on air-dried, acetone fixed cytospins and the corresponding formalin fixed, paraffin embedded cell block using an avidin-biotin immunoperoxidase method.
Positive immunoreactivity revealed a granular cytoplasmic staining in melanocytic cells. The current study results showed that 92% of samples (57 of 62) were T311 immunoreactive on cell block preparations, whereas only 61% (38 of 62) were immunoreactive on cytospin preparations. In 66% of samples (41 of 62) immunoreactivity for T311 was greater in the cell block sample than in the corresponding cytospin, whereas in only 3% of samples (2 of 62) was it greater in the cytospins. In 31% of samples (19 of 62) there was no significant difference in immunoreactivity between the 2 sample types.
The results of the current study show that tyrosinase is a sensitive marker for the detection of MMM; however, the optimal method of sample preparation for immunoperoxidase staining appears to be formalin fixation and paraffin embedding as tyrosinase immunoreactivity is diminished significantly in air-dried cytospin samples despite subsequent acetone fixation. Cancer (Cancer Cytopathol)