Background: Primary malignant melanomas of the Gastric mucosa are uncommon. Most cases of Gastrointestinal (GI) melanomas are secondary, arising from metastasis at distant sites. GI melanomas have been associated with dismal prognosis, owing to their identification at more advanced stages. The purpose of this study is to investigate the clinical characteristics, survival outcomes, and prognostic factors of patients with primary GI melanoma in the past decade. Methods: A total of 399 patients diagnosed with Primary GI melanoma, between 2008 and 2017, were ultimately enrolled in our study by retrieving the Surveillance, Epidemiology, and End Results (SEER) database. We analyzed demographics, clinical characteristics, and overall mortality (OM) as well as cancer-specific mortality (CSM) of primary GI melanoma. Variables with a p value < 0.1 in the univariate Cox regression were incorporated into the multivariate Cox model to determine the independent prognostic factors, with a hazard ratio (HR) of greater than 1 representing adverse prognostic factors.Results: From a sample of 399 primary GI melanomas, male gender (56.4%), age range 60-79 years (52.88%), non-Hispanic whites (70.18%), as well as annual income of $75,000+ yearly (30.33%) were the most represented. Crude analysis revealed higher overall mortality (OM) in age group 80+ (HR = 4.042, 95% CI 1.732 - 9.433, p = 0.001), stomach location of the tumor (HR = 3.261, 95% CI 1.658 - 6.417, p = 0.001), distant metastases (HR = 2.967, 95% CI 2.22 - 3.965, p=0 ), Nonmetropolitan counties not adjacent to a metropolitan area ( HR= 2.211, 95 % CI 1.253-3.9, p=0.006 ), and chemotherapy ( HR= 1.417, 95% CI 1.078-1.863, p=0.012). Crude analysis for Cancer specific mortality (CSM) also revealed higher mortality in the same groups. Multivariate cox proportional hazard regression analyses only revealed higher OM in age group 80+ (HR = 5.653, 95% CI 2.212 - 14.445, p=0), stomach location of the tumor (HR = 2.821, 95% CI 1.265 - 6.292, p = 0.011), and distant metastases (HR= 4.491, 95% CI 3.115-6.476, p=0). Multivariate cox proportional hazard regression analyses of CSM also revealed higher mortality of the same groups.Conclusion: Primary GI melanoma is a rare entity. Only a few studies have been carried out in recent years to evaluate factors affecting the survival and mortality of primary GI melanoma. The paucity of data on primary GI melanoma governed the need of this study. In this population-based retrospective cohort study using the SEER database, we found that age at diagnosis, the primary site of the disease, and advanced disease at diagnosis were independent factors predicting poor prognosis. Furthermore, even surgical resection did not significantly impact the overall mortality or the cancer-specific mortality. This cohort paves the path for further prospective studies identifying individuals at an increased risk of primary GI melanomas, earlier and closer screenings in such individuals, and then evaluation of long-term prognosis in these patients as age and advanced disease were both independent risk factors predicting poor prognosis in our study.

1. Background: Primary malignant melanomas of the Gastric mucosa are uncommon. Most cases of Gastrointestinal (GI) melanomas are secondary, arising from metastasis at distant sites. GI melanomas have been associated with dismal prognosis, owing to their identification at more advanced stages. The purpose of this study is to investigate the clinical characteristics, survival outcomes, and prognostic factors of patients with primary GI melanoma in the past decade. 2. Methods: A total of 399 patients diagnosed with Primary GI melanoma, between 2008 and 2017, were ultimately enrolled in our study by retrieving the Surveillance, Epidemiology, and End Results (SEER) database. We analyzed demographics, clinical characteristics, and overall mortality (OM) as well as cancer-specific mortality (CSM) of primary GI melanoma. Variables with a p value < 0.1 in the univariate Cox regression were incorporated into the multivariate Cox model to determine the independent prognostic factors, with a hazard ratio (HR) of greater than 1 representing adverse prognostic factors. 3. Results: From a sample of 399 primary GI melanomas, male gender (56.4%), age range 60-79 years (52.88%), non-Hispanic whites (70.18%), as well as annual income of $75,000+ yearly (30.33%) were the most represented. Crude analysis revealed higher overall mortality (OM) in age group 80+ (HR = 4.042, 95% CI 1.732 - 9.433, p = 0.001), stomach location of the tumor (HR = 3.261, 95% CI 1.658 - 6.417, p = 0.001), distant metastases (HR = 2.967, 95% CI 2.22 - 3.965, p=0 ), Nonmetropolitan counties not adjacent to a metropolitan area ( HR= 2.211, 95 % CI 1.253-3.9, p=0.006 ), and chemotherapy ( HR= 1.417, 95% CI 1.078-1.863, p=0.012). Crude analysis for Cancer specific mortality (CSM) also revealed higher mortality in the same groups. Multivariate cox proportional hazard regression analyses only revealed higher OM in age group 80+ (HR = 5.653, 95% CI 2.212 - 14.445, p=0), stomach location of the tumor (HR = 2.821, 95% CI 1.265 - 6.292, p = 0.011), and distant metastases (HR= 4.491, 95% CI 3.115-6.476, p=0). Multivariate cox proportional hazard regression analyses of CSM also revealed higher mortality of the same groups.4. Conclusion: Primary GI melanoma is a rare entity. Only a few studies have been carried out in recent years to evaluate factors affecting the survival and mortality of primary GI melanoma. The paucity of data on primary GI melanoma governed the need of this study. In this population-based retrospective cohort study using the SEER database, we found that age at diagnosis, the primary site of the disease, and advanced disease at diagnosis were independent factors predicting poor prognosis. Furthermore, even surgical resection did not significantly impact the overall mortality or the cancer-specific mortality. This cohort paves the path for further prospective studies identifying individuals at an increased risk of primary GI melanomas, earlier and closer screenings in such individuals, and then evaluation of long-term prognosis in these patients as age and advanced disease were both independent risk factors predicting poor prognosis in our study.