Malignant melanoma (MM) arising in a giant pigmented nevus (GPN) is a rare disease in adults with no large series published to our knowledge.

We sought to describe the characteristics, treatment, and survival of MM in GPN for adults.

Adults with invasive MM in GPN (n = 976) reported to the National Cancer Data Base from 1998 to 2012 were evaluated for patient and tumor characteristics, treatment, and survival. For comparison, data from adults with invasive superficial spreading melanoma (SSM) (n = 111,870) and nodular melanoma (n = 35,962) were used.

Compared with patients with SSM, patients with MM in GPN had a thicker Breslow depth, more positive lymph nodes, and distant metastasis more frequently. Multivariate analysis identified age older than 65 years, Breslow thickness greater than 2 mm, presence of ulceration, presence of distant metastasis, and positive margins as independent predictors of survival in patients with MM in GPN. At all stages, having MM in GPN has similar overall survival compared with SSM.

The study is retrospective and registry-based.

Invasive MM in GPN occurs in adults, with overall survival similar to SSM. Clinicians should be aware of the continued risk of MM in adults with GPN with low threshold for biopsy.