Main Session
Sep
29
PQA 07 - Head and Neck Cancer, Lung Cancer/Thoracic Malignancies, and Nursing and Supportive Care
3521 - Exploring the Prognostic Value of Tumor Regression after 4 Weeks of Radiotherapy in Oropharyngeal Cancer
Presenter(s)
Isaac Lasko, MD - Loyola University Medical Center, Maywood, IL
I. Lasko1, M. Bhandari2, V. Fahmy2, J. Bergman3, E. Thorpe3, A. Ziegler3, and A. M. Block4; 1Department of Radiation Oncology, Stritch School of Medicine, Cardinal Bernardin Cancer Center, Loyola University Chicago, Maywood, IL, 2Department of Radiation Oncology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL, 3Department of Otolaryngology, Loyola University Medical Center, Maywood, IL, 4Department of Radiation Oncology, Cardinal Bernardin Cancer Center, Loyola University Medical Center, Maywood, IL
Purpose/Objective(s):
Patients with oropharyngeal squamous cell carcinoma (SCC) risk significant morbidity from both treatment and disease progression. Improved risk stratification may help guide treatment escalation or de-escalation; tumor hypoxia, p16 status, and HPV DNA show prognostic value, but early imaging biomarkers during radiotherapy remain underexplored. The purpose of this study is to evaluate whether interim tumor regression assessed on cone-beam CT (CBCT) and changes in post-treatment FDG PET SUV independently predict for locoregional recurrence-free survival (LRRFS).Materials/Methods:
This is a single institutional retrospective review of patients with locally advanced oropharyngeal cancer treated with definitive radiotherapy (RT), with or without concurrent chemotherapy, from 2015 to 2025. All patients had image-guided RT (IGRT) including at least weekly CBCT. Demographic, tumor, and treatment data were collected. Primary and nodal gross tumors were contoured both at baseline CT simulation and on CBCT after 4 weeks of RT, then tumor regression was defined as the percent change of total tumor volume. The percent change from baseline to post-treatment SUV-max on FDG PET was also calculated. Stage grouping incorporated p16 status per AJCC 8th edition. Kaplan-meier analysis and univariable (UVA) and multivariable (MVA) cox proportional hazard models for LRRFS were performed. Covariates with p<0.1 on UVA were allowed in MVA.Results:
127 eligible patients were included with median follow-up 29.1 months. Median age was 65. Smoking histories were 37% never, 53% former, and 10% current. 76% had p16+ tumors. Radiotherapy was delivered to median dose 70 Gy (IQR 70-70). 94.5% underwent concurrent chemotherapy. In the overall cohort, 3-year OS and LRRFS were 86.4% and 78.9%, respectively. The median change in tumor size after 4 weeks of RT was -41.6% (IQR: -32.0 to -53.9; range: 19.4 to -78.7). Tumor regression of =40% vs <40% led to 3-year LRRFS of 85% vs 74% (log rank p=0.049). On MVA, tumor regression (HR 0.73 per -10%, p=0.027) and stage (III/IV vs. I/II, HR 4.68, p=0.001) independently predicted for LRRFS, while smoking status did not (ever vs. never, HR 2.53, p=0.16). 109 patients had baseline and post-treatment PET scans (median 3.0 months after completion of RT) available for SUV analysis. 50.5% had complete metabolic response in post-treatment PET/CT. Of the 49.5% with residual uptake, the median decrease in SUV-max was -70.1% (IQR: -59.5 to -78.6). Complete vs partial metabolic response led to 3-year LRRFS of 87% vs 75% (log rank p=0.054). On MVA, SUV-max decrease (HR 0.7 per -10%, p=0.004) and stage (III/IV vs. I/II, HR 2.83, p=0.04) independently predicted LRRFS.Conclusion:
In this cohort of patients undergoing RT for oropharyngeal SCC, tumor regression on CBCT after 4 weeks of radiotherapy independently predicted LRRFS. Validation in larger prospective cohorts may facilitate incorporation of interim tumor regression into evolving risk-stratification strategies.