[Detection of circulating neoplastic cells by reverse transcriptase and polymerase chain reaction in melanoma]

Circulating melanocytes can be detected in peripheral blood of patients with malignant melanoma by means of tyrosinase messenger RNA amplification. In this study we especially examined peripheral blood from patients with stage II melanoma before and after lymph node dissection for the detection of these circulating melanoma cells. Indeed the presence of regional nodal metastasis is one of the most important prognostic factors in patients with cutaneous melanoma.

Blood samples were collected from 20 normal patients, 42 patients with stage I melanoma and 23 patients with stage III melanoma. Twenty patients with stage II melanoma were tested 3 days before lymph node dissection and 2 à 8 weeks after. To identify circulating melanocytes, we used coupled reverse-transcription and polymerase chain reaction to target tyrosinase messenger RNA.

None of the 20 patients with stage II melanoma had detectable circulating melanocytes before lymph node dissection. By contrast, 7 of them became transiently PCR positive in the 8 weeks following surgery. We observed no evidence of correlation between the presence of circulating melanocytes after lymph node dissection and the risk of relapse within 6 months after surgery or the presence of capsule breaking or the number of involved lymph nodes. Sixty-nine percent of stage III patients and none of stage I patients were found to have circulating melanocytes.

Our study suggests that melanoma cells could circulate transiently after lymph node dissection. Confrontation of our results with literature data, despite important discrepancies related in part to sensibility technique, shows that the presence of circulating melanoma cells is correlated to the clinical stage. Prognostic value of these circulating cells need to be further assessed by prospective studies with large number of patients and long follow-up.