Outcome of Patients Treated with Neoadjuvant Concurrent Chemoradiation for Signet Ring Cell Rectal Carcinoma

Background: Signet-ring cell carcinoma (SRCC) of the rectum is a rare and aggressive subtype of colorectal cancer, often presenting at a younger age and with advanced disease. It has historically shown limited response to standard neoadjuvant chemoradiotherapy (CRT), with poor long-term outcomes. This study aimed to evaluate short-term clinical and pathological outcomes following neoadjuvant concurrent CRT in patients with rectal SRCC. Methods: This descriptive case series included 30 patients with histologically confirmed rectal SRCC treated between December 2023 and December 2024. All received induction CapeOX chemotherapy followed by CRT and total mesorectal excision (TME). Radiological response was assessed using RECIST 1.1 criteria and MRI. Primary outcomes included pathological complete response (pCR) and downstaging; secondary outcomes included R0 resection rates and treatment-related toxicities. Results: The median age was 42 years; 60% of patients presented with stage III disease. Of 29 patients who completed CRT, 26 underwent surgery. Pathological complete response was achieved in 15.4%, and 57.7% had overall downstaging. R0 resection was accomplished in 88.5%. Radiologically, 27.6% had partial response, 62.1% had stable disease, and no complete radiological responses were observed. Treatment-related grade 3 toxicities occurred in 40% of patients. No treatment-related mortality was reported. Conclusion: Neoadjuvant concurrent CRT in rectal SRCC resulted in modest tumor regression and a pCR rate consistent with previous literature. However, the majority of patients proceeded to successful resection with acceptable toxicity. These findings support the feasibility of an intensified neoadjuvant approach in this histologically aggressive subtype, although long-term survival benefits remain to be established.