Background: Anorectal malignant melanoma (ARMM) is extremely rare and generally lethal, irrespective of the treatment administered. The disease is often diagnosed late, metastases being present in approximately two-third of patients at the time of initial diagnosis. Solitary metastasis of ARMM to a distant organ is exceedingly rare. To the best of our knowledge, only two cases of hepatic resection for a synchronous solitary liver metastasis from a primary ARMM have been reported, and only one

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... hepatic resection for a metachronous solitary liver metastasis after excision of a primary ARMM. Additionally, we did not find any previous reports of multidisciplinary therapy incorporating surgery and a full course of adjuvant therapy for the latter condition. Case presentation: A 76-year-old woman with a history of laparoscopic abdominoperineal resection of an ARMM 13 months previously was found to have a solitary liver metastasis on follow-up computed tomography. A preoperative work-up showed no other distant metastases nor contraindication to surgery. It was therefore considered that resection was indicated. The metachronous solitary liver metastasis from an ARMM was treated by laparoscopic wedge hepatectomy of the eighth segment 18 months after excision of her primary ARMM. Adjuvant therapy with pembrolizumab was initiated and continued at 6-week intervals. The patient has now completed 12 months of adjuvant pembrolizumab therapy, having survived 33 months from the initial operation for primary ARMM, and remaining recurrence-free 14 months after hepatectomy.Conclusions: We here report a rare case of hepatectomy for a solitary metachronous liver metastasis after resection of a primary ARMM, followed by completion of 12 months of adjuvant therapy with pembrolizumab. ARMM is extremely rare and resection of a metachronous solitary metastasis followed by adjuvant therapy has not previously been reported. We hope this case will be useful for clinicians treating similar patients.