A case report of metastatic mixed adeno-neuroendocrine carcinoma of the anus presenting as anal pain

INTRODUCTION: Mixed adeno-neuroendocrine carcinoma (MANEC) is a rare disease, and much of the available literature to date has consisted of case reports. A recent systematic review revealed heterogeneity in the data as not all reports documented treatment regimens and course of disease. The recent 2019 WHO update on neuroendocrine carcinoma nomenclature adds to the pre-existing classification system based on biologic activity, to better represent the spectrum of neuroendocrine non-neuroendocrine tumours (Frizziero et al., 2020). PRESENTATION OF CASE: We present a case of a patient who presented with anal pain, had a wide local excision which on histopathology revealed poorly differentiated MANEC. Despite adjuvant chemotherapy with cisplatin and etoposide as well as pelvic radiotherapy, the patient developed bi-lobar liver metastases within 9 months of initial presentation. The patient succumbed to colonic perforation 10 months after initial presentation. DISCUSSION: Most patients present with advanced disease with site-specific symptoms, and despite treatment of localised disease, many recur with distant metastasis. CONCLUSION: Although rare, this disease is highly aggressive, thus it is hoped that more clinicians can be made aware about its various clinical manifestations and disease course.