Submucosal-dominant, stricture-type rectosigmoid adenocarcinoma with false-negative biopsies: a case report

Background Endoscopic biopsy is the standard for diagnosing colorectal cancer. However, infiltrative tumors presenting as annular strictures may yield non-diagnostic samples, risking significant treatment delay. Case presentation: An 82-year-old man presented with loose stools and hematochezia. Colonoscopy revealed a tight, non-traversable rectosigmoid stricture; repeated mucosal biopsies were negative for malignancy. Contrast-enhanced computed tomography (CT) demonstrated concerning features, including circumferential mural thickening, luminal narrowing, and small pericolic nodules. Due to persistent high clinicoradiologic suspicion despite negative biopsies, the patient underwent laparoscopic low anterior resection. Final histopathology confirmed a moderately-to-poorly differentiated adenocarcinoma, staged as pT3N1c, with lymphovascular invasion, perineural invasion, and intermediate tumor budding. Conclusions This case highlights the diagnostic limitations of superficial mucosal biopsy in submucosal-dominant, stricturing colorectal lesions. It underscores the critical importance of multidisciplinary, probability-driven decision-making when histologic findings contradict strong clinical and imaging evidence of malignancy. In such scenarios, proceeding to timely surgical resection is paramount to avoid progression to emergency presentation and to facilitate appropriate adjuvant therapy.