New Zealand has the highest rate of melanoma-related mortality in the world. Access to immunotherapy and radiology is limited and surgical treatment of regional disease remains important. A recent pilot study of a single health district observed a higher nodal melanoma burden than was reported in the second Multicentre Selective Lymphadenectomy Trial (MSLT-II). In this study, a series of regional censuses were undertaken covering the 10 years immediately prior to the publication of MSLT-II. The study population was seven District Health Boards covering 62.2% of the population of New Zealand across a 10-year period preceding MSLT-II. The primary outcomes measured were the size of sentinel lymph node metastases and non-sentinel node (NSN) positivity on completion lymph node dissection (CLND) for patients with a positive sentinel lymph node biopsy (SLNB). In the 2323 SLNB identified, the mean sentinel lymph node metastatic deposit size was larger compared to MSLT-II (2.55 vs. 1.07/1.11 mm). A greater proportion of New Zealand patients (44.2%) had metastatic deposits larger than 1 mm compared to MSLT-II (33.2/34.5%) and the rate of non-sentinel node involvement on CLND was also higher (22.2% vs. 11.5%). These findings indicate that New Zealand is a high-risk population for nodal melanoma metastases. Due to these differences, the conclusions of MSLT-II may not be able to be applied to melanoma patients in the 7 regions studied in New Zealand.
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