Photodynamic therapy combined with radiofrequency ablation and systemic therapy for KRAS-mutant advanced low rectal cancer: A case report.

The overall incidence of colorectal cancer, particularly the lower part of the rectum normally known as low rectal cancer, is globally on the rise, accounting for approximately 10% of all new oncology cases. KRAS, a common oncogenic mutant gene, has a mutation frequency of up to 40% in colorectal cancer and significantly impacts its prognosis and therapeutic outcomes. Anatomically, low rectal cancer usually develops in a deep and narrow pelvic space, adjacent to critical nerves and organs, posing significant challenges for radical resection. A 52-year-old female presented with an extremely low-lying locally advanced rectal cancer or tumor exhibiting high-risk features with an intravascular tumor thrombus and high proliferative activity. This patient initially underwent an endoscopic photodynamic therapy combined with "oxaliplatin + capecitabine" chemotherapy, bevacizumab, and sintilimab monotherapy, resulting in some significant tumor shrinkage and decrease in volume. Subsequent sequential therapeutic strategies included radiofrequency ablation, second-line chemotherapy combined with bevacizumab, and sintilimab. Following 15 months of intensive neoadjuvant conversion therapy, the tumor continued to decrease in size, ultimately enabling successful radical abdominoperineal resection with rectal resection. This case demonstrates a remarkable successful application of a novel treatment strategy combining photodynamic therapy with radiofrequency ablation for local treatment alongside systemic therapy to give room to surgical opportunities for patients with locally advanced ultra-low rectal cancer.