The number of nodal basins and the number of lymph nodes containing regional metastases are important prognostic factors in patients with truncal malignant melanoma. Because the lymphatic drainage pattern of truncal melanoma often includes more than 1 basin, we designed a study to evaluate whether: (1) patients with dual-basin drainage were at an increased risk of lymph node metastases identified by sentinel lymph node (SLN) biopsy; and (2) the histologic status of an individual basin reliably predicted the status of the other draining basin in patients with dual-basin drainage.

The records of 269 consecutive patients with melanoma, who were treated primarily with intraoperative lymphatic mapping and SLN biopsy between 1997 and 2002, were reviewed. Of these patients, 122 had primary truncal melanomas. All patients underwent preoperative lymphoscintigraphy, which established the number and location of draining nodal basins. The chi-square and Fisher's exact tests of relevant clinicopathologic factors determined which factors were predictive of the presence of a pathologically positive SLN.

At least one SLN was identified in all patients. Dual-basin drainage was present in 39 (32%) patients, and a pathologically positive SLN was found in 12 (31%) of these patients. By chi-square and Fisher's exact tests, dual-basin drainage was not a significant independent risk factor for the presence of at least 1 pathologically positive SLN (P = .846). Tumor thickness (P < .001), Clark level (P = .003), and tumor ulceration (P = .003) were significant independent risk factors for the presence of at least 1 pathologically positive SLN. SLN pathology in one basin did not predict the histology of the other basin in 7 (18%) of 39 patients with dual-basin drainage.

Dual-basin drainage is not independently associated with an increased risk of nodal metastases in patients with truncal melanoma. Because the histologic status of an individual basin did not reliably predict the status of the other draining basins in patients with dual-basin drainage, it is important to adequately identify and completely assess all nodal basins at risk, as defined by lymphoscintigraphy, in patients with truncal melanoma.