Cause-specific colostomy rates after radiotherapy for anal cancer: a Danish multicentre cohort study

In anal cancer, colostomy-free survival is a measure of anal sphincter preservation after treatment with radiotherapy or chemoradiotherapy. Failure to control anal cancer and complications of treatment are alternative indications for colostomy. However, no data exist on cause-specific colostomy rates. We examined this in a cohort study.

Through national registries and review of medical records, we identified patients with anal cancer diagnosed from 1995 to 2003 who had curative-intent radiotherapy or chemoradiotherapy in four Danish centers. We computed cumulative incidence of tumor-related colostomy and therapy-related colostomy, treating colostomy and death as competing events. Follow-up started at completion of radiotherapy and continued throughout 2008. We used competing risk regression to compute hazard ratios (HRs) to compare the cumulative incidence of cause-specific colostomies between age, sex, tumor size, chemotherapy, and local excision before radiotherapy.

We included 235 patients with anal cancer. The 5-year cumulative incidences of tumor-related and therapy-related colostomy were 26% (95% CI, 21% to 32%) and 8% (95% CI, 5% to 12%), respectively. Tumor size greater than 6 cm versus less than 4 cm was a risk factor for tumor-related colostomy (adjusted HR, 3.8; 95% CI, 1.7 to 8.1), and local excision before radiotherapy was a risk factor for therapy-related colostomy (adjusted HR, 4.5; 95% CI, 1.5 to 13.5).

After curative-intent radiotherapy or chemoradiotherapy, one third of patients had a colostomy, of which one third were related to therapy. Large tumor size was associated with a higher risk of tumor-related colostomy, whereas history of prior excision was associated with an increased incidence of therapy-related colostomy.