When controlling for tumor present in the Sentinel lymph node (SLN), intranodal hypoxia, as measured by Carbonic Anhydrase IX (CAIX IHC), is associated with worse PFS. This suggests that melanoma tumors may be utilizing deregulated metabolism as a means of propagating themselves to the next station of metastasis. This study aims to prospectively validate previous findings. Patients who are to undergo WLE and SLNB per standard of care (SOC) will be evaluable. It is hypothesized that SLN(s) with increased hypoxia, as measured by pimonidazole staining, will be associated with worse Progression-free Survival (PFS).