Early-Stage Rectal Mixed Neuroendocrine-Non-neuroendocrine Neoplasm Treated With Local Excision in a Frail Elderly Patient: A Multidisciplinary Management Dilemma.

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Mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs) of the rectum are rare tumors that typically demonstrate aggressive behavior, largely driven by high-grade neuroendocrine carcinoma components. Evidence guiding management is limited, particularly for early-stage lesions and for patients unable to tolerate standard oncologic surgery. We report the case of an elderly man with extensive comorbidities who was found to have a 1.3 cm rectal MiNEN following transanal endoscopic microsurgery (TEMS) performed for rectal bleeding. Histopathology revealed a moderately differentiated adenocarcinoma component and a well-differentiated grade 1 neuroendocrine tumor (NET) component, with submucosal invasion greater than 2 mm, negative margins, low tumor budding, small-vessel lymphovascular invasion (LVI), and intact mismatch repair protein expression. No lymph nodes were sampled. Given the patient's extensive comorbidities, progressive neurologic disease (including Parkinsonism and dementia), and reduced functional independence, he was considered a high-risk candidate for radical oncologic resection. The patient's neurologic impairment and overall functional status were the primary factors limiting surgical escalation, rather than isolated cardiometabolic comorbidities alone. A surveillance-based approach with external expert pathology review was recommended. This case highlights the complexity of managing early-stage rectal MiNENs in medically vulnerable patients and underscores the importance of individualized, multidisciplinary decision-making when guideline-directed therapy is not feasible.

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