Radiation Therapy and Malignant Fistulae of Anorectal Cancers

Although fistulization is a well-studied late toxic effect of radiation therapy (RT), anorectal cancers (ARCs) can present with malignant fistulae (MF) and negatively affect quality of life. The effect of RT, often combined with concurrent chemotherapy, on MF needs systematic analysis, because practitioners are concerned that RT may exacerbate MF. We reviewed our institutional series evaluating the hypothesis that RT worsens MF.

A single-institutional retrospective analysis of patients with ARC receiving RT from 2006 to 2019 was performed. These patients were screened for MF. Any MF resected before RT and RT not directed at the site of MF were excluded. Effects were assessed by review of available follow-up documentation and imaging.

A total of 639 patients with ARC were reviewed, and 47 had MF (7.4%). With a median follow-up of 22 months (range, 2-133 months), RT improved MF in 17 of 29 evaluable patients (59%), with 9 of 29 (31.0%) having resolution. The median time to improvement was 50 days (range, 25-117 days); the median duration of improvement was 161 days (range, 0-1941 days). Malignant fistulae persisted in 12 of 29 patients (41%), with persistent local disease in all cases; in 2 cases, MF worsened concomitant with local progression.

In all, 7.4% of patients with ARC presented with MF. Radiation therapy led to improvement or resolution in more than half of evaluable patients. Persistence or worsening of MF was only observed in patients with refractory or progressive local disease. Based on our findings, MF is not a contraindication to RT and may be considered as an independent indication for palliative RT.