POLYMERASE-CHAIN-REACTION AND IMMUNOHISTOCHEMISTRY FREQUENTLY DETECT OCCULT MELANOMA-CELLS IN REGIONAL LYMPH-NODES OF MELANOMA PATIENTS

Aims-To evaluate immunohistochemistry and reverse transcriptase polyme rase chain reaction (RT-PCR) for melanoma associated antigens (MAA) in detecting occult melanoma cells in lymph nodes which were missed on r outine pathology. Methods-Occult melanoma cells were sought in 436 lym ph nodes from 32 patients with cutaneous melanoma of the lower extremi ties by immunohistochemistry using the melanoma specific antibody HMB- 45. The detection sensitivity of routine histology, immunohistochemist ry, and RT-PCR was also compared in 23 lymph node samples from six pat ients. Results-Immunohistochemistry showed that 15 of 24 patients (62. 5%) who had no detectable metastasis by routine histology had at least one lymph node containing HMB-45 positive cells, mostly seen singly i n the medullary sinus. No difference was found in known clinicopatholo gical prognostic factors and recurrence rates between the two groups o f patients with and without occult HMB-45 positive cells. RT-PCR analy ses showed that the nested PCR for tyrosinase was more sensitive than a combination of single round PCR for five different MAA, including ty rosinase, MART-1/Melan A, Pmel-17, TRP-1, and TRP-2, detecting tyrosin ase mRNA in six nodes which were negative by HMB-45 immunohistochemist ry. Conclusions-Immunohistochemistry + RT-PCR is more sensitive than r outine histology in detecting occult melanoma cells in lymph nodes. Th e nested PCR for tyrosinase should be used in future studies investiga ting the prognostic significance of such lymph node micrometastases.