Abstract
ObjectivesTo assess the effectiveness of fluorine-18 fluorodeoxyglucose (FDG) positron-emission tomography-computed tomography (PET-CT) and magnetic resonance imaging (MRI) for response assessment post curative-intent chemoradiotherapy (CRT) in anal squamous cell carcinoma (ASCC).MethodsConsecutive ASCC patients treated with curative-intent CRT at a single centre between January 2018 and April 2020 were retrospectively identified. Clinical meta-data including progression-free survival (PFS) and overall survival (OS) outcomes were collated. Three radiologists evaluated PET-CT and MRI using qualitative response assessment criteria and agreed in consensus. Two-proportion z test was used to compare diagnostic performance metrics (sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), accuracy). Kaplan-Meier analysis (Mantel-Cox log-rank) was performed.ResultsMRI (accuracy 76%, PPV 44.8%, NPV 95.7%) and PET-CT (accuracy 69.3%, PPV 36.7%, NPV 91.1%) performance metrics were similar; when combined, there were statistically significant improvements (accuracy 94.7%, PPV 78.9%, NPV 100%). Kaplan-Meier analysis demonstrated significant differences in PFS between responders and non-responders at PET-CT (p = 0.007), MRI (p = 0.005), and consensus evaluation (p < 0.001). Cox regression analysis of PFS demonstrated a lower hazard ratio (HR) and narrower 95% confidence intervals for consensus findings (HR = 0.093, p < 0.001). Seventy-five patients, of which 52 (69.3%) were females, with median follow-up of 17.8 months (range 5–32.6) were included. Fifteen of the 75 (20%) had persistent anorectal and/or nodal disease after CRT. Three patients died, median time to death 6.2 months (range 5–18.3).ConclusionCombined PET-CT and MRI response assessment post-CRT better predicts subsequent outcome than either modality alone. This could have valuable clinical benefits by guiding personalised risk-adapted patient follow-up.Key Points• MRI and PET-CT performance metrics for assessing response following chemoradiotherapy (CRT) in patients with anal squamous cell carcinoma (ASCC) were similar.• Combined MRI and PET-CT treatment response assessment 3 months after CRT in patients with ASCC was demonstrated to be superior to either modality alone.• A combined MRI and PET-CT assessment 3 months after CRT in patients with ASCC has the potential to improve accuracy and guide optimal patient management with a greater ability to predict outcome than either modality alone
Highlights
Anal cancer is rare, accounting for 1.5% of digestive tract cancers with a worldwide incidence of 1 in 100,000 and rising prevalence in developed countries [1–3]
Combined magnetic resonance imaging (MRI) and positron-emission tomography-computed tomography (PET-CT) treatment response assessment 3 months after CRT in patients with anal squamous cell carcinoma (ASCC) was demonstrated to be superior to either modality alone
Ninety percent are of squamous cell histology (ASCC), with the most prevalent risk factor being human papillomavirus (HPV) [4–7]
Summary
Anal cancer is rare, accounting for 1.5% of digestive tract cancers with a worldwide incidence of 1 in 100,000 and rising prevalence in developed countries [1–3]. Ninety percent are of squamous cell histology (ASCC), with the most prevalent risk factor being human papillomavirus (HPV) [4–7]. Diagnosis and local staging are performed with a combination of physical examination, digital rectal examination, biopsy and pelvic magnetic resonance imaging (MRI). The mainstay of curative treatment for non-metastatic ASCC includes external-beam radiotherapy with concurrent mitomycin C and 5-fluorouracil or capecitabine [10]. A recent prospective, national cohort study using contemporary chemoradiotherapy (CRT) techniques reported 1-year overall survival (OS) rates of 94%, disease-free survival (DFS) of 84% and colostomy-free survival at 86% [11]. Surgical treatment is largely reserved for salvage therapy in cases of CRT failure or recurrence. Post-CRT follow-up assessment, including high-quality imaging, is of key importance for early identification of residual or recurrent disease
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