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The management of metastatic squamous cell carcinoma of the anus (SCCA) is based on systemic chemotherapy. Recently, docetaxel, cisplatin and 5-Fluorouracil (DCF) was defined as a new option in patients with advanced SCCA with an objective response rate of 88%. The role of a complementary pelvic chemoradiation (CRT) is unknown in this setting. In this study, we reported the safety and efficacy of local CRT in patients with synchronous metastatic SCCA with an objective response after upfront DCF.

Patients with advanced SCCA treated with either standard DCF regimen (sDCF, docetaxel 75 mg/m² on day 1, cisplatin 75 mg/m² on day 1, and 5-Fluorouracile (5FU) 750 mg/m² by 24 hours continuous infusion for 5 days, every 21 days) or modified DCF regimen (mDCF, docetaxel 40 mg/m² on day 1, cisplatin 40 mg/m² on day 1, and 5FU 1200 mg/m² per day for 2 days, every 14 days), followed by pelvic CRT were included. Concurrent chemotherapy was based on mitomycin (MMC) (10 mg/m² for two cycles) and fluoropyrimidine (capecitabine 825 mg/m² twice a day at each RT treatment day or two cycles of intra-venous 5FU 1000 mg/m² from day 1 to day 4). 

From 2013 to 2018, 16 patients received DCF followed by a complementary pelvic CRT for advanced SCCA. The median number of DCF cycles was 6 for sDCF and 8 for mDCF. All patients received the complete radiation dose. RT had to be interrupted because of acute toxicity in four patients (25%), one of which had a scheduled gap. All patients received concurrent MMC and fluoropyrimidine, but only 4 patients (25%) received the whole scheduled dose of chemotherapy. Regarding CRT tolerance, 13/15 of the patients (87%) had at least one grade 1-2 acute toxicity, and 11/15 of the patients (73%) had at least one grade 3-4 toxicity. There was no treatment-related death. The most frequent grade 3-4 adverse effects were neutropenia (36%), dermatitis (40%), and anitis (47%). Eleven patients (73%) had at least one chronic grade 1 or 2 toxicity such as rectitis, fibrosis or incontinence. One patient had a grade 4 chronic rectitis (7%). The complete local response rate was 81% at first evaluation and 62.5% at the end of the follow-up. The 1-year local PFS rate was 73% (95%CI 61.9-84.6) and the 3-year local PFS rate was 67% (95%CI 54.5-78.8). The median PFS was 14.9 months (2.1-54.6), the 1-year PFS rate was 62.5% (95%CI 50.4-74.6) and the 3-year PFS rate was 33% (95%CI 19.5-46.1). The median OS was not reached. The 1-year OS rate was 87.5% (95%CI 79.2-95.8) and the 3-year OS rate was 75 % (95%CI 64.2-85.8).

In patients with metastatic SCCA who had a significant objective response after upfront DCF, local CRT was feasible with high complete local response rate. The compliance with concurrent chemotherapy was low. The good local control rate despite interruptions due to toxicities and low CT compliance, underline the role of pelvic RT. The high rate of toxicity prompt the need to adapt the CRT regimen in the metastatic setting.