An incomplete picture: challenges of partial biopsies in large diameter atypical melanocytic lesions

Large diameter atypical pigmented lesions (LDAPL) can be challenging to diagnose accurately using partial biopsies because of pathologic heterogeneity, while at the same time large excisions of these lesions confer significant morbidity to patients. Consequently, clinicians are often challenged by the management of these lesions. In this case, we describe an elderly patient with a history of multiple basal cell carcinomas, prior melanomas, and a family history of melanoma who presented with an irregularly pigmented brown and dark brown patch on his upper back. This lesion was evaluated with multiple partial incisional biopsies from the most atypical appearing areas of the lesion identified on dermoscopy, each showing mild and moderate atypical melanocytes. However, the patch continued to change clinically and eventually the patient underwent a 5mm wide local excision, which revealed severely atypical melanocytic proliferation with areas consistent with melanoma in situ. This case highlights the need for clinicians to lower their threshold for excisional biopsy of LDAPL in high-risk patients.