Interval sentinel lymph nodes in patients with cutaneous melanoma: a single-institution study in Japan

Interval sentinel lymph nodes (ISLN) are defined as the lymph nodes located between the primary melanoma and anatomically well-defined lymph nodal basins. It was reported that the ISLN appeared to be at the same metastatic risk as sentinel lymph nodes (SLN) in the traditional nodal basins. This study aimed to examine the incidence and metastatic risk of the ISLN in melanoma patients. Between June of 1999 and December of 2008, 117 patients enrolled at Nagoya University Hospital underwent SLN biopsy for primary cutaneous melanoma with a Breslow thickness of at least 1.0 mm. Triple techniques with lymphoscintigraphy, blue dye injection and gamma probe were used for the biopsy except for 13 cases that underwent lymphoscintigraphy, ultrasonography and blue dye injection, but without gamma probe. Patients who had melanoma of the head and neck were excluded from this analysis. The SLN were identified in 253 nodal basins from 117 patients, and ISLN were found in six patients (5%). We recognized 41 (17%) SLN metastases in 246 conventional nodal basins and one (14%) in seven ISLN. Although ISLN were identified infrequently, the incidence of metastasis into the ISLN was similar to that into SLN in conventional nodal basins. It is therefore recommended that preoperative lymphoscintigraphy and intraoperative recognition of ISLN should be performed.