May CJ, Piepkorn MW, Knezevich SR, et al. - In order to better understand current practices of immunohistochemical (IHC) testing, researchers sought to determine the case, pathologist, and interpretative factors associated with the utilization of IHC for melanocytic tumors. One hundred eighty-seven pathologists from 10 US states analyzed a test set of 240 skin biopsies of melanocytic tumors, identifying 48 cases in Phase I and either 36 or 48 cases in Phase II. Of 187 candidates interpreting 48 cases each, 21 (11%) did not request IHC testing in any case, 85 (45%) requested testing in 1 to 6 cases, and 81 (43%) requested testing in ≥ 6 cases. Findings suggested an association of increased utilization of testing with younger age of pathologist, board‐certification in dermatopathology, low confidence in diagnosis, and lesions in intermediate MPATH‐Dx classes 2 to 4. It was noted that the median intraobserver concordance for requesting tests among 72 candidates interpreting the same 48 cases in Phases I and II was 81% and the median Kappa statistic was 0.20. Findings revealed that there is considerable variation among pathologists in using IHC.