O09 From skin to gut: the journey of metastatic melanoma in the gastrointestinal tract

Abstract Melanoma is the most common solid tumour that can spread to the gastrointestinal tract (GIT), although the GIT remains a less common site for melanoma metastases. Melanoma GIT metastases can present with vague symptoms and may emerge years following a primary melanoma. This retrospective study analysed consecutive patients with GIT metastatic melanoma at a UK tertiary centre (July 2002 to March 2023). Data were collected on patient demographics, primary melanoma characteristics, presentation of GIT metastases and outcomes. There were 122 patients (44 female, 78 male; mean age 64 years). The majority (75%, n = 92) of GIT metastases were in the small bowel. The GIT was a single site of metastasis in 22% (n = 27) of patients, while 95 (78%) had other visceral metastases. The mean time to GIT metastases was 6.1 years (range 3–359 months) among patients with a cutaneous primary (n = 102). Around one-third of these (30%, n = 31) presented after being discharged from melanoma follow-up. Twenty (16%) of the total cohort of 122 patients presented with GIT metastases with unknown primary; in 40% of these GIT metastases were the first presentation of melanoma. Overall, 30% (n = 36) with GIT metastases had previously had stage I melanoma. In total, 16% (16 of 102) had had melanoma with Breslow thickness < 1 mm. Anaemia was seen in 70% (86 of 122). Common presenting symptoms included abdominal pain (n = 40), GI bleed (n = 19) and GI obstruction (n = 11). Fourteen patients were asymptomatic. Three-quarters (75%, n = 92) of GIT metastases were diagnosed with computed tomography and 15% (n = 18) with endoscopy. Thirty-four patients required both investigations as the result for the first investigation was normal. Thirty-eight patients had surgery for GIT metastases. Small bowel resection (n = 33) was the most common surgery. The overall median survival was 11 months [95% confidence interval (CI) 8–14]. The median follow-up time was 27 months. The median survival for patients who had surgery was 33 months (95% CI 13–54). Overall, 83 had systemic treatment. The median survival for patients who had first-line immunotherapy was 44 months (95% CI 13–88), compared with 8 months (95% CI 3–15) for those who had first-line targeted therapy. In BRAF mutant melanoma, patients treated with targeted therapy first line had worse survival than those receiving immunotherapy, with a hazard ratio of 5.2 (95% CI 2–13) and P-value < 0.001 (log-rank test). Any patients with a history of invasive melanoma of any stage presenting with anaemia and/or GI symptoms even years after should be suspected to have GIT metastases. Endoscopy is unlikely to detect small bowel metastases. Computed tomography scans are often sufficient for diagnosis, with particular attention to the small bowel, which can be missed unless highlighted. Isolated GIT metastases may be surgically resected with improved outcome. Patients treated with first-line immunotherapy have better overall survival than those treated with first-line targeted therapy.