Posttreatment FDG-PET-CT Response via PERCIST Criteria is Predictive of Tumor Prognosis in Anal Carcinoma

Abstract

We hypothesize that posttreatment F-18 fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) is useful to evaluate metabolic response in patients with anal cancer, specifically via the Positron Emission Tomography (PET) Response Criteria in Solid Tumors (PERCIST).This was a single-institution retrospective review of 62 patients treated with Nigro Regimen chemoradiation therapy for anal squamous cell carcinoma between 2008 and 2020. All patients had pretreatment PET-CT scan and were followed with posttreatment PET-CT scans and clinical examinations. PERCIST criteria was utilized to evaluate the treatment response to chemoradiation therapy. If a target lesion shows complete resolution of FDG uptake, the response is complete metabolic response (CMR). If the decrease from baseline to follow-up is greater than or equal to 30%, the response is partial metabolic response (PMR). If the decrease is less than 30% or if the lesion shows an increase of FDG uptake less than 30%, the response is stable metabolic disease (SMD). If the target lesion shows a 30% increase or higher FDG uptake, or if there is a new lesion, the response is disease progression (DP).The median follow-up was 38 months (range, 7-114 months). Pretreatment PET-CT detected the primary tumor in 62 cases (100%), the inguinal lymph nodes were FDG avid in 33 patients, and the pelvic lymph nodes were FDG avid in 39 patients. Initial posttreatment PET-CT was obtained on average 3 months after the last day of radiation. The evaluation of the primary anal tumor on initial follow-up PET-CT showed CMR in 31 patients (50%), PMR in 26 patients (42%), and SMD in 5 patients (8%). No patients showed disease progression (DP, 0%). The evaluation of the largest inguinal node on initial post treatment PET-CT showed CMR in 30 patients (91%), PMR in 3 patients (9%), without evidence of progression of groin lymphadenopathy. The evaluation of the largest pelvic node on initial post treatment PET-CT showed CMR in 36 patients (92%), PMR in 1 patient (3%), and SMD in 2 patients (5%), without evidence of progression of pelvic lymphadenopathy.The PERCIST criteria is a reliable and useful technique in evaluating treatment response for the primary anal cancer as well as the inguinal and pelvic lymphadenopathy. The Nigro protocol is a promising combined chemoradiation therapy strategy for the anal cancer patients with most demonstrating complete metabolic response or partial metabolic response on the initial post treatment FDG PET-CT scan.