Standard versus reduced-dose chemoradiotherapy in anal cancer (PLATO-ACT4): short-term results of a phase 2 randomised controlled trial

Abstract

Background: Localised squamous cell carcinoma of the anus is treated with radical chemoradiotherapy. Cure rates are high, but treatment can result in substantial acute and long-term morbidity. We aimed to assess whether lower dose chemoradiotherapy maintains high local control rates in patients with early-stage disease, with the secondary aim of reducing toxicity.

Methods: ACT4 is a phase 2, prospective, multicentre, open-label, two-arm non-comparative, randomised, controlled trial, investigating reduced-dose intensity-modulated radiotherapy (rd-IMRT: 41·4 Gy in 23 fractions) in patients with early-stage anal cancer; T1-2 (≤4 cm) N0-NxM0. Eligible patients were at least 16 years of age, with an Eastern Cooperative Oncology Group performance status of 0-1. The primary outcome is 3-year loco-regional failure rates. Patients were randomly assigned 1:2 (with stratification by T stage, N stage, gender, HIV status, and randomising site) to standard-dose IMRT (sd-IMRT: 50·4 Gy in 28 fractions) or rd-IMRT with concurrent mitomycin and capecitabine chemotherapy. Here, we report the pre-planned, modified intention-to-treat analysis of secondary endpoints 6 months after treatment end-complete clinical response, compliance, patient-reported outcomes (EORTC QLQ-C30 and ANL27), and safety data. The trial is registered at the ISRCTN registry (ISRCTN88455282) and is ongoing but no longer recruiting.

Findings: 163 patients were recruited from 28 UK tertiary centres between April 24, 2017, and Dec 1, 2020. 160 patients were included in the primary analysis (sd-IMRT n=55; dr-IMRT n=105). Data on ethnicity were not collected. The median patient age was 66 years (IQR 58-72 years); 117 (73%) were female and 43 (27%) male; and 129 (94%) of 138 evaluable samples were p16 positive. Complete clinical responses at 6 months were 87% (46 of 53) for sd-IMRT and 92% (89 of 97) for rd-IMRT. Radiotherapy interruptions of 3 days or more occurred in 14 (26%) of 55 patients in sd-IMRT and 16 (15%) of 105 patients in rd-IMRT. Chemotherapy modifications occurred in 27 (49%) of 55 patients in sd-IMRT and 39 (37%) of 105 patients in rd-IMRT. Grade 3 or worse acute toxicity was reported in 25 (46%) of 55 patients in sd-IMRT and 37 (35%) of 105 patients in rd-IMRT. The most common grade 3 or worse adverse events were radiation dermatitis (seven [13%] of 55 in sd-IMRT and ten [10%] of 105 in rd-IMRT), and diarrhoea (four [7%] of 55 in sd-IMRT and nine [9%] of 105 in rd-IMRT). Serious adverse events occurred in eight (15%) of 55 patients in sd-IMRT and ten (10%) of 105 patients in rd-IMRT. Patient-reported outcomes for most issues deteriorated at the end of treatment and resolved to baseline by 6 weeks in both groups. Poorer sexual function for men and women was observed at 6 months following sd-IMRT.

Interpretation: Good 6-month complete clinical responses rates were seen in both groups. Early results suggest rd-IMRT is well tolerated with oncological outcomes maintained. 3-year locoregional failure rates are awaited.

Funding: Cancer Research UK and Stand Up to Cancer.