Characteristics, treatment, and outcomes of anal versus rectal squamous cell carcinoma, a retrospective cohort study

Although squamous cell carcinoma is the most common malignancy of the anal canal, it rarely affects the rectum. The present study aimed to assess the differences in characteristics, treatments, clinical and pathologic outcomes, and survival between anal and rectal squamous cell carcinoma.

The United States National Cancer Databases (2004-2020) of anal canal and rectal cancer were used for this retrospective cohort analysis. Patients with anal or rectal squamous cell carcinoma were included in the analysis. The study's primary outcome was overall survival, and secondary outcomes were 30-day and 90-day mortality, 30-day readmission, and positive resection margins.

The present study included 76,830 patients with anal squamous cell carcinoma and 7,908 with rectal squamous cell carcinoma. Patients with anal squamous cell carcinoma presented more often with early clinical stage I and stage II disease (50.4% vs 45.9%, P < .001) and less often with stage IV disease (6.5% vs 15.1%, P < .001). Anal squamous cell carcinomas were more often treated with upfront surgery than were rectal squamous cell carcinomas (37.7% vs 19.7%, P < .001), whereas rectal squamous cell carcinomas were more often treated with chemoradiation therapy alone (68.3% vs 59.8%, P < .001). Anal squamous cell carcinomas were treated more often with local excision (33.4% vs 15.8%, P < .001) than rectal squamous cell carcinoma. Anal squamous cell carcinoma was associated with a higher incidence of positive resection margins (41.9% vs 32.8%, P < .001). The 30-day and 90-day mortality rates were higher after surgery for rectal squamous cell carcinoma than for anal squamous cell carcinoma (1.5% vs 0.4% and 4.1% vs 1.6%, respectively, P < .001). Anal squamous cell carcinoma had longer median overall survival (145.3 vs 90.3 months, P < .001) than rectal squamous cell carcinoma.

Patients with anal squamous cell carcinoma presented more often with early-stage disease and less often with distant metastasis and were more often treated with upfront surgery, mainly local excision. Anal squamous cell carcinoma was associated with lower 30-day and 90-day mortality and longer overall survival than rectal squamous cell carcinoma.