Epidemiology and survival outcomes of primary gastrointestinal melanoma: a SEER-based population study

Primary melanoma arising in the gastrointestinal (GI) tract is rare and poorly characterized. We sought to describe the epidemiology and survival outcomes of primary GI melanoma.

GI melanoma cases were extracted from the Surveillance, Epidemiology, and End Results (SEER) database by tumor site and histology codes. We calculated age-adjusted incidence, and analyzed demographics, clinical characteristics, as well as overall survival (OS) and cancer-specific survival (CSS) of GI melanoma.

A total of 1080 histologically confirmed cases of primary GI melanoma were identified, with a median age of 71 years (IQR: 59-80). 49.9% of the cases originated from anus, 30.8% had distant disease at diagnosis, and 61.5% received cancer-directed surgery. The distribution of gender and age was varied in GI melanoma subtypes. The incidence of GI melanoma was 0.58 cases per million, and increased remarkably over age, especially in patients aged 60 years or older. The median OS and CSS of the whole cohort was 14 months (95% CI 12.7-15.3) and 22 months (95% CI 18.8-25.2), respectively. Anal melanoma patients had prolonged survival, while those with gastric melanoma had the poorest OS (18 and 4 months, respectively). Multivariate analysis showed that decreased survival was associated with age older than 80 years, gastric and esophageal origin, advanced-stage disease, lymph node metastasis, and without surgery of primary site.

Patients with primary GI melanoma trended to present with advanced-stage disease. Overall, GI melanoma had a poor prognosis, but the outcome differed according to the primary sites.