Radioisotopic lymphatic mapping of the sentinel node in melanoma: Importance of immunohistochemistry

Background: Elective lymph node dissection (ELND) for patients with malignant melanoma is still controversial. A possible alternative could be biopsy of the first tumor draining lymph node, the sentinel node (SN), which can be identified by means of radionuclide techniques. Aim: Our study was undertaken to assess the accuracy of lymph node biopsy and to stress the importance of immunohistochemistry (IHC) in the pathological assessment of the SN for improved staging of the primary tumor. Methods: We performed lymphoscintigraphy (LS) in 183 melanoma patients (89 with melanoma of the legs, 11 of the arms and 83 of the trunk). Our protocol consisted of preoperative peritumoral i.d. injection of Tc-99m-labeled microcolloid to define the regional lymphatic basin and identify the sentinel node by means of planar scintigraphy. In 147 of the 183 cases a gamma probe (GP) was used during surgery to trace the SN. Vital blue dye was used during surgery in all cases. The SNs were excised for pathological examination, The pathological status of the SN was defined by means of examination of frozen sections, hematoxylin-eosin staining and immunohistochemistry for S-100 and HMB-45 MAb. Results: At least one separate focus of activity was identified by LS in 182 out of 183 patients; in all 147 cases where a GP was used, it was successful in tracing the SN, LS with cutaneous mapping of the SN successfully guided the surgical excision in 177 of the 183 cases; in the 7 remaining cases, i.e. 7 out of 83 cases with SNs in the axillary basin, GP was not used and no elective node dissection was performed. Metastases were found in 39 of these 177 cases. In all 39 cases the SNs were the only positive nodes in the basin. Of the 39 metastases 18 were identified by means of frozen section, 12 by means of hematoxylin-eosin, and 9 by means of immunohistochemistry. We therefore emphasize the importance of immunohistochemistry in the pathology of LS for improved staging of the primary tumor.