The histopathologic diagnosis of some melanocytic tumors is extraordinarily difficult. With this in mind, melanocytic tumors from patients referred to the Massachusetts General Hospital (MGH) Pigmented Lesion Clinic (PLC) are routinely reviewed in the MGH Dermatopathology Unit.

We sought to determine the frequency of diagnostically challenging cases from patients treated at the MGH PLC, as measured by a change in the diagnosis upon review of the referral materials.

We retrospectively reviewed the MGH and referral pathology reports for 478 consecutive cutaneous melanocytic tumors: 126 from 1996-1997 and 352 from 2010-2011. Differences in diagnosis and in therapeutic impact were evaluated.

Changes in diagnosis occurred in 168 of 478 cases (35%), more frequently when the original diagnostician was a general pathologist (P = .003). A similar fraction of diagnoses were changed from malignant to benign or vice versa, in both historic and contemporary cohorts. In 64 patients (13%), changes in diagnosis led to a change in therapy. Changes in stage or grading led to the most changes in therapy (78%; 50/64) versus changes from benign to malignant or vice versa (22%; 14/64).

This is a retrospective study with the bias of a tertiary-care referral center.

These findings demonstrate the diagnostic difficulty of a subset of melanocytic tumors and highlight the utility of review by more than one pathologist; patient treatment is affected in more than 10% of cases. Identification of melanoma prognostic factors and melanocytic nevus grading led to clinically significant changes in diagnosis leading to a change in patient management.