The Predictive Value of Post-Treatment PET-CT Imaging for Patients With Curable Anal Canal Cancer

Abstract

<h3>Purpose/Objective(s)</h3> According to 2020 "NCCN" guidelines, post-treatment positron emission tomography (PET) – computed tomography (CT) imaging of the body is <b>not</b> recommended to predict outcomes of patients undergoing curative intent chemoradiation therapy (CRT) for anal canal cancer. This study used PERCIST (Positron Emission tomography Response Criteria In Solid Tumors) to evaluate CRT response and outcomes for our patient population at a single institution. <h3>Materials/Methods</h3> Our "IRB"-approved anal canal database was queried for patients who have undergone CRT, modified "NIGRO" protocol, for carcinoma of the anal canal. The evaluable patient dataset comprised those with both pre- and post-CRT PET-CT imaging of the body. The primary study endpoint was relapse-free survival (RFS) calculated from date of diagnosis to date of first known appearance of disease or death from any cause. Overall survival (OS) was defined using elapsed time between date of diagnosis and date of death and surviving patients were censored using date of last follow-up. Also, the range and median time to first post-CRT PET-CT imaging was determined. RFS and OS were analyzed using Kaplan-Meier method. Complete response rate (CRR) and objective response rate (ORR) were calculated along with 95% confidence intervals using Fisher's exact method. All tests were two-sided, and statistical significance was considered when <i>P</i> < 0.05. <h3>Results</h3> Out of an initial 392 patients in our database registry, 62 had pre/post-CRT PET-CT imaging from June 2008 until May 2020. There were 18 males and 44 females. The median age at diagnosis was 57.7 years (range: 38-84 years). "AJCC" (7^th edition) staging distribution was as follows: 3 Stage I, 13 Stage II, 41 Stage III, and 5 Stage IV. The median total dose of external beam irradiation was 54 Gy (range: 45-60 Gy). Time to post-CRT PET-CT imaging ranged from 0.2 to 27.8 months (mos) [median: 2.9 mos]. Respective PET-response rates regarding primary tumor (N = 62); largest groin node (N = 33); and largest pelvic node (N = 39) were as follows: 31 CR (Complete Response), 26 PR (Partial Response), 5 SD (Stable Disease), and 0 DP (Disease Progression); 30 CR, 3 PR, 0 SD, 0 DP; and 36 CR, 1 PR, 2 SD, 0 DP. Patient follow-up ranged from 6.8 to 114 mos (median: 38.6 mos). At time of last follow-up, there were 53 alive and 9 dead. Estimated 3-year RFS was 72% (95% "CI": 58.2-81.9%). Estimated 3-year OS was 88.8% (95% CI: 76.6-94.9%). Respective CRRs and ORRs for the primary tumor were 50% (95% CI = 37-63%) and 91.9% (95% CI = 82.2-97.3%); for the groin node 48.4% (95% CI = 35.5-61.4%) and 53.2% (95% CI = 40.1-66%); and for the pelvic node 58.1% (95% CI = 44.8-70.5%) and 59.7% (95% CI = 46.4-71.9%). CRRs and ORRs were not significant prognostic factors for either RFS or OS. <h3>Conclusion</h3> After applying PERCIST to our institutional study cohort, the use of post-treatment PET-CT imaging to predict outcomes for this patient population remains unproven.