Conversion Surgery after Chemotherapy in a Stage IV V600E-Mutated Laterally Spreading Tumor With Neuroendocrine Component.

We report a rare case of a V600E-mutated laterally spreading tumor, granular type (LST-G), with a neuroendocrine carcinoma (NEC) component in a patient with stage IV colorectal cancer. The patient presented with multiple lymph nodes and liver metastases. Following systemic chemotherapy, significant regression of both the primary lesion and metastases was achieved, enabling successful conversion surgery. Postoperative pathological analysis post-surgery revealed only well-differentiated tubular adenocarcinoma, with complete disappearance of the NEC component. Molecular testing confirmed the persistence of the V600E mutation. The patient remains recurrence-free two years after surgery. This case highlights the potential for conversion surgery in stage IV -mutated colorectal cancer with NEC.