Metastatic Melanoma to the Colon, Rectum, and Anus: A 50-Year Experience

Melanoma metastatic to the large bowel (colon, rectum, and anus) is rarely diagnosed, with more than 95% of large bowel metastases identified post-mortem. The incidence, natural history, and survival rates of patients with large bowel melanoma metastases are poorly documented in the literature.

This study aimed to identify the incidence, clinical characteristics, and survival of patients with large bowel melanoma metastases.

A review was undertaken of all patients with melanoma treated over a 50-year period (1964-2014) at a tertiary referral center. Cases selected for study were those diagnosed with melanoma metastases in the colon, rectum, and anus. Primary colorectal and anal melanomas were excluded. Data were retrieved relating to patient demographics, clinical features, and survival.

Of 38,279 patients with primary melanoma, 106 patients (0.3%, mean age 51.0 years [standard deviation 16.3], 64 males) developed large bowel metastases. The median interval between diagnosis of primary melanoma and large bowel metastasis was 62.8 months (range 1-476). The most common symptom was rectal bleeding (29.2%), and the large bowel was the sole site of metastasis in 47.2% of patients. Median survival from diagnosis of large bowel metastasis was 31.7 months (range 1-315), and overall survival at 1, 2, and 5 years was 68.1, 45.9, and 26.5%, respectively.

Our study provides insights into melanoma metastatic to the colon, rectum, and anus, which had an incidence of 0.3%. There are potentially long intervals between diagnosis of primary melanoma and large bowel metastasis. The most common symptom was rectal bleeding, although some patients were asymptomatic.