19 | Late draining lymph nodes on preoperative lymphoscintigraphy in melanoma patients: preliminary data from a retrospective study of over 400 cases

Background: Sentinel lymph node biopsy (SLNB) in melanoma allows the identification of patients with clinically non-palpable metastatic lymph nodes. The risk of nodal involvement is related to Breslow thickness, ulceration, or mitotic rate. SLN can be identified in almost all treated cases, with a false-negative rate of 5% and a relatively low local complication rate (10%). Preoperative dynamic lymphoscintigraphy using radiocolloid (Tc99) is mandatory to correctly identify the SLN to be excised. Segmental preoperative lymphoscintigraphy sometimes reveals lymph nodes that only appear during delayed imaging and not during the dynamic phase.Methods: This retrospective study aims to: analyze the percentage of SLN identified intraoperatively; assess the incidence of metastatic lymph nodes; compare disease-free survival and overall survival between study group and general population, stratified by Breslow thickness; identify possible risk factors and causes associated with late lymph node detection.Results: All patients who underwent SLNB at the Plastic Surgery Unit of the San Gallicano Institute, IRCCS, IFO, Rome, from 2004 to 2019, were analyzed. 665 patients showed delayed drainage on preoperative lymphoscintigraphy. Among these, 448 patients were included in the study due to complete data availability. The mean age was 56 years. In only 9 cases (2%), the SLN could not be found intraoperatively. The sentinel node was metastatic in 15% of cases, regardless of Breslow thickness or ulceration (36%). The incidence of late-draining lymph nodes by Breslow thickness was as follows: 11% in pT1a, 21% in pT1b, 15% in pT2a, 13% in pT2b, 4% in pT3a, 6% in pT3b, 4% in pT4a, 8% in pT4b.Conclusions: Analysis revealed a higher prevalence of late drainage in melanomas with Breslow thickness <2 mm. Late drainage does not preclude successful SLN identification. The incidence of lymph node metastases was lower than average, although larger cohort studies are necessary to provide more comprehensive data.