545P - Feasibility of chemoradiotherapy in rectal cancer patients with peritumoral abscesses and fistulas: A case-control non-inferiority trial

Neoadjuvant chemoradiotherapy (CRT) is a standard treatment for patients with locally advanced rectal cancer and is effective as a palliative care in patients with nonresectable tumors. Unfortunately CRT is often being withheld for patients with tumor-associated complications due to safety concerns. Literature search reveals only case reports and neither supports nor declines additional risks of CRT in this patient group. The aim of this study was to determine feasibility of CRT in rectal cancer with peritumoral abscesses and fistulas. Patients with locally advanced or recurrent rectal cancer with peritumoral abscesses and fistulas were included in the study group. The control group consisted of T4 locally advanced or recurrent rectal cancer patients without complications, both groups received long-course neoadjuvant CRT. Groups were matched by age, previous treatment, treatment year. The primary endpoint was CRT toxicity. Secondary endpoints included postoperative morbidity (Clavien-Dindo), pathologic complete response (pCR) and 2year PFS. 30 patients were included in each group. Patients in the main group had following tumor-associated complications: perianal fistula (n=11), abdominal wall fistula (n=1), rectovaginal fistula (n=9), rectovesical fistula (n=4), peritumoral abscess (n=17). Grade 3-4 toxicity was observed in 2 (6.66%) vs 3 (10%) patients, non-inferiority was confirmed (p=0.0326). Grade 3-4 postoperative complications were observed in 2 (7.14%) patients in the main group and in 3 (10.7%) patients in the control group (p=0.639) with no cases of mortality. pCR was achieved in 2 (7.14%) and 5 (17.8%) patients accordingly (p=0.225). Median follow-up was 25.2 months in the main group and 27.4 months in the control group. Two-year OS was 69% vs 100% (p=0.11), 2-year PFS was 65% vs 78% (p=0.434). Peritumoral abscesses and fistulas should not be considered as contraindication to neoadjuvant chemoradiotherapy. CRT is feasible and safe in patients with tumor-associated complications. The authors. Has not received any funding. All authors have declared no conflicts of interest.