Pathologic review of negative sentinel lymph nodes in melanoma patients with regional recurrence: a clinicopathologic study of 1152 patients undergoing sentinel lymph node biopsy.

A sentinel lymph node (SLN) that is melanoma negative by pathologic examination implies absence of melanoma metastasis to that regional lymph node field. However, a small proportion of patients develop regional node field recurrence after a negative SLN biopsy. In this study, we reviewed the histopathology of negative SLNs from such patients to determine whether occult melanoma cells were present in the SLNs, to characterize the pathologic features of false-negative SLNs, and to provide recommendations for the histopathologic examination of these specimens. Between March 1992 and June 2001, of 1152 patients who had undergone SLN biopsy for primary melanomas at the Sydney Melanoma Unit, 976 were diagnosed with negative SLNs by initial pathologic examination (using 2 hematoxylin and eosin stained sections, and 2 immunostained sections for S-100 protein and HMB45), and follow-up was available in 957. Of these, 26 (2.7%) developed regional lymph node recurrence during a median follow-up period of 35.7 months. For 22 of them, the original slides and tissue blocks were available for reexamination. The original slides of each block were reviewed. Multiple further sections were cut from each block and stained with hematoxylin and eosin, for S-100, HMB45, and Melan A. Deposits of occult melanoma cells were detected in 7 of the 22 cases (31.8%). In 5 of the 7 cases, deposits of melanoma cells were present only in the recut sections. There were no significant differences in clinical and pathologic variables for those patients in whom occult melanoma cells were found by pathologic reexamination of their SLNs, compared with those in whom no melanoma cells were detected. The detection of melanoma cell deposits in only 7 of 22 false-negative SLNs suggests that mechanisms other than failure of histopathologic examination may contribute to the failure of the SLN biopsy technique in some patients. The failure rate for melanoma detection in SLNs by our routine pathologic examination, using the current protocol at our institution, was <1% (7 of 957 patients). Routinely performing more intensive histopathologic examination of SLNs is difficult to justify from a cost benefit perspective; we therefore recommend examining two hematoxylin and eosin stained sections and two immunostained sections (for S-100 and HMB45) routinely on SLNs from melanoma patients.