The progression of melanoma nodal metastasis is dependent on tumor thickness of the primary lesion

Background: Recent results of several clinical trials using the technique o f intraoperative lymphatic mapping and sentinel lymph node (SLN) biopsy con firm the validity of the concept of there being an order to the progression of melanoma nodal metastases. This report reviews the H. Lee: Moffitt Canc er Center experience with this procedure, one of the largest series describ ed to date. These data demonstrate that the involvement of the SLNs, as wel l as higher-echelon nodes, is directly proportional to the melanoma tumor t hickness, as measured by the method of Breslow. Methods: The investigators at the H. Lee Moffitt Cancer Center retrospectiv ely reviewed their experience using lymphatic mapping and SLN biopsies in t he treatment of malignant melanoma. All eligible patients with primary mali gnant melanomas underwent preoperative and intraoperative mapping of the ly mphatic drainage of their primary sites, along with SLN biopsies. All patie nts with positive SLNs underwent complete regional basin nodal dissection. For 20 consecutive patients with one positive SLN, all of the nodes from th e complete lymphadenectomy were serially sectioned and examined by S-100 im munohistochemical analysis, to detect additional metastatic disease. Results: Six hundred ninety-three patients consented to undergo lymphatic m apping and SLN biopsy. The SLNs were successfully identified and collected for 688 patients, yielding a 99% success rate. One hundred patients (14.52% ) showed evidence of nodal metastasis. The rates of SLN involvement for pri mary tumors with thicknesses of <0.76 mm, 0.76-1.0 mm, 1.0-1.5 mm, 1.5-4.0 mm, and >4.0 mm were 0%, 5.3%, 8%, 19%, and 29%, respectively. Eighty-one p atients underwent complete lymph node dissection after observation of a pos itive SLN, and only six patients with positive SLNs demonstrated metastatic disease beyond the SLN (7.4%). The tumor thicknesses for these six patient s ranged from 2.8 to 6.0 mm. No patient with a tumor thickness of <2.8 mm w as found to have: evidence of metastatic disease beyond the SLN in complete lymph node dissection. All 20 patients with a positive SLN for whom all of the regional nodes were serially sectioned and examined by S-100 immunohis tochemical analysis failed to show additional positive nodes. Conclusions: These results suggest that regional lymph node involvement may be dependent on the thickness of the primary tumor. As the:primary tumor t hickness increases, so does the likelihood of involvement of SLNs and highe r regional nodes in the basin beyond the positive SLNs.