Optimal time for MRI response evaluation in squamous cell carcinoma of the anus

Bettina A Hanekamp; Ellen Viktil; Johann Baptist Dormagen; Nils E Kløw; Cathrine Brunborg; Eirik Malinen; Marianne G Guren; Anselm Schulz

doi:10.1093/bjro/tzag004

Optimal time for MRI response evaluation in squamous cell carcinoma of the anus

BJR Open. 2026 Feb 11;8(1):tzag004. doi: 10.1093/bjro/tzag004. eCollection 2026 Jan.

Authors

Bettina A Hanekamp^{1

2}, Ellen Viktil^{1

2}, Johann Baptist Dormagen², Nils E Kløw^{1

2}, Cathrine Brunborg³, Eirik Malinen^{4

5}, Marianne G Guren^{1

6}, Anselm Schulz^{1

2}

Affiliations

¹ Institute of Clinical Medicine, University of Oslo, 0318 Oslo, Norway.
² Department of Radiology, Oslo University Hospital, 0424 Oslo, Norway.
³ Oslo Centre for Biostatistics and Epidemiology, Oslo University Hospital, 0424 Oslo, Norway.
⁴ Department of Physics, University of Oslo, 0316 Oslo, Norway.
⁵ Department of Radiation Biology, Oslo University Hospital, 0310 Oslo, Norway.
⁶ Department of Oncology, Oslo University Hospital, 0310 Oslo, Norway.

Abstract

Objectives: To identify the optimal time for MRI response evaluation after chemoradiotherapy (CRT) in squamous cell carcinoma of the anus (SCCA) and to employ combined T2+diffusion-weighted MRI tumour regression grade (comrTRG).

Methods: We assessed the positive and negative predictive values (PPV, NPV) of post-treatment MRI in a retrospective mono-centre diagnostic accuracy study that prospectively included consecutive patients treated between 2013 and 2017. Index tests were MRI at 6-, 12-, and 24-weeks post-treatment (6w, 12w, and 24w) to detect locoregional treatment failures (LRTF). Clinical outcome served as reference standard. Tumour regression was assessed using comrTRG based on radiological reports. Mixed-effects logistic regression was used to compare the comrTRG score across time points. The analyses were stratified by patients' T/N stage and human papillomavirus (HPV) status.

Results: For 127 included patients (62 years ± 11 [mean ± SD]; 92 women), 261 post-treatment MRI reports (6w: n = 45, 12w: n = 125, 24w: n = 91) were scored using comrTRG. LRTF occurred in 13 patients; 12/13 were high-risk patients (T3/T4, N+, or HPV-negative); 1/13 progressed early (<24 weeks). The rate of radiologic complete response (comrTRG1) increased over time (6w: 27%, 12w: 66%, 24w: 75%), while the rate of indeterminate (comrTRG2) and minor definite tumour (comrTRG3) decreased. PPV of MRI increased over time: 6w: 33% (95%CI: 9.9%-65.1%), 12w: 46% (16.7%-76.6%), and 24w: 88% (47.3%-99.7%). NPV was stable high >90%.

Conclusions: MRI performed more reliably after 24 weeks. Timely assessment may aid early LRTF detection. Tailoring follow-up with frequent MRI scans may be sufficient for high-risk patients. Combined mrTRG is practical for describing response in SCCA.

Advances in knowledge: Post-treatment MRI assessment at later time points is preferable in SCCA to avoid inconclusive imaging and unnecessary salvage surgery. The introduced comrTRG is a practical tool for response evaluation.

Registration: ClinicalTrials.gov: NCT01937780.

Keywords: anal cancer; chemoradiotherapy; diffusion magnetic resonance imaging; response assessment; treatment failure.

Associated data

ClinicalTrials.gov/NCT01937780