Treating a Non-mixed Neuroendocrine Colorectal Tumor Under Mixed Neuroendocrine Neoplasm (MiNEN) Protocols: A Case Report of Successful Outlier Management.

A 65-year-old male presented after a positive Cologuard testing. He was asymptomatic at presentation, with no reported complaints of fever, chills, abdominal pain, diarrhea, constipation, hematochezia, or unexpected weight loss. CT imaging of the abdomen and pelvis revealed a 2 cm mass at the rectosigmoid junction with a single enlarged lymph node nearby measuring 2.7 x 1.6 cm, raising suspicion for regional metastatic adenopathy. He underwent a colonoscopy, which confirmed a rectosigmoid mass. Biopsy results showed adenocarcinoma of the colon. Consequently, the patient was scheduled for a laparoscopic sigmoidectomy with low anterior resection. The pathology of the surgical specimen confirmed adenocarcinoma, moderately differentiated, associated with a component of poorly differentiated large cell neuroendocrine carcinoma, with the neuroendocrine component best developed in the lymph node metastasis. Although the patient did not meet the standard criteria for mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN) tumors, treatment was administered using chemotherapeutic agents typically reserved for MiNENs. He was treated with platinum-based doublet with good response and has been in remission for one and a half years. This report highlights the importance of flexible therapeutic approaches when pathology marginally deviates from the standard established criteria, illustrating that tailoring treatment to the specific pathology can provide considerable patient benefits.