# Pathological Complete Response Achieved with Colorectal Cancer-Based Chemotherapy for Locally Recurrent Cecal Neuroendocrine Carcinoma after Surgery: A Case Report

## TL;DR

A rare case of cecal neuroendocrine carcinoma achieved full recovery using chemotherapy typically used for colorectal cancer, suggesting new treatment possibilities.

## Contribution

First reported case of cecal neuroendocrine carcinoma achieving pathological complete response with colorectal cancer-based chemotherapy.

## Key findings

- Colorectal cancer-based chemotherapy (FOLFOXIRI plus bevacizumab) led to pathological complete response in recurrent cecal NEC.
- CEA levels normalized and imaging showed regression after treatment, indicating effective therapy.
- This case suggests CEA can guide chemotherapy selection for neuroendocrine carcinoma.

## Abstract

Primary neuroendocrine carcinoma (NEC) of the colon is extremely rare, accounting for only 0.2% of all colorectal malignancies, and is associated with a poor prognosis. Early diagnosis is often challenging, as endoscopic biopsies are frequently misinterpreted as adenocarcinoma. Although platinum-based regimens such as etoposide plus cisplatin or irinotecan are commonly used, no standard chemotherapy protocol has been established. We report a case of locally recurrent cecal NEC that responded remarkably to a colorectal cancer–based chemotherapy regimen, achieving a pathological complete response.

A 52-year-old man presented with severe anemia. Imaging and colonoscopy revealed a cecal tumor initially diagnosed as adenocarcinoma. He underwent laparoscopic right hemicolectomy with lymph node dissection. Final pathology revealed NEC, staged as pT3N2aM0, Stage IIIB. Adjuvant etoposide–cisplatin chemotherapy was initiated. Three months postoperatively, carcinoembryonic antigen (CEA) rose to 44.4 ng/mL, and CT demonstrated a perianastomotic peritoneal nodule and lymphadenopathy, consistent with recurrence. Considering the adenocarcinoma component in the primary tumor and elevated CEA, chemotherapy was switched to a colorectal cancer–based regimen: FOLFOXIRI plus bevacizumab. After 7 cycles, both radiologic regression and normalization of CEA levels were achieved. Resection of the recurrent lesions confirmed a pathological complete response with no residual tumor cells.

To the best of our knowledge, this is the first reported case of cecal NEC achieving pathological complete regression with a colorectal cancer–based chemotherapy regimen. Our findings indicate that colorectal NEC may respond not only to platinum-based regimens but also to colorectal cancer–based regimens. Furthermore, CEA levels may serve as a clinically relevant biomarker to guide chemotherapy selection in this setting.