Challenges in sentinel node (SN) pathology in the era of adjuvant treatment: The risk of over and undertreatment stress the need for expert pathology review.

Abstract

9593 Background: With the approval of adjuvant therapy for stage III melanoma, accurate staging in melanoma patients is important more than ever to prevent over- or undertreatment. Sentinel node biopsy (SNB) is an accurate staging tool, yet the presence of capsular nevi (CN) can lead to a false positive diagnosis. We compared positive SNB and CN patient outcomes and aimed to evaluate the cause of false positive SNB and discern diagnostic pitfalls in their evaluation. Methods: Retrospective analysis of AJCC 7th Edition stage IIIA melanoma patients (N1-2a, non-ulcerated primary tumor) who were treated at our institute between 2000 and 2015. SNB slides were reviewed for this study by an expert melanoma pathologist. Baseline characteristics were assessed for SN+ and CN+ patients. Concordance rates for SNB evaluation before and after revision were documented and diagnostic pitfalls were discerned. Results: 169 patients were diagnosed, 10 could not be reviewed due to lack of evaluable slides. Of these 159 cases, 14 patients originally diagnosed with metastatic melanoma were shown to have capsular nevi (8.8%). Another 2 patients were shown to have melanophages that were incorrectly interpreted as metastases (1.3%). Thus, 10.1% was considered false positive after revision. In 14 patients the SN tumor burden was originally reported > 1 mm, but turned out to have < 1 mm SN tumor burden. 4 patients originally reported as SN tumor burden < 1 mm before revision turned out to have > 1 mm SN tumor burden. These 32 patients (20%) might have potentially been over- or undertreated in the current era of adjuvant therapy for stage III melanoma. Conclusions: False positive sentinel node results in melanoma are real, they can occur for a number of reasons, but distinguishing metastatic melanoma from benign capsular nevi and melanophages can be a diagnostic challenge. We plead for an expert pathologists’ review in any case, but certainly when using the SNB+ results to determine treatment consequences for SN+ melanoma patients.