Abstract PO-056: The effect of timing of post-operative radiation on outcomes in anaplastic thyroid cancer

Abstract Introduction: Anaplastic thyroid cancer is an aggressive malignancy for which prompt treatment is necessary. Surgical resection is the recommended initial treatment for resectable cases and most patients require postoperative radiation therapy (RT). NCCN Guidelines state that adjuvant radiation should ideally begin 2-3 weeks postoperatively, however, limited evidence exists to support this guideline. Herein, we examine the National Cancer Database (NCDB) to assess whether the time interval between surgery and RT start impacts overall survival (OS). Methods: An NCDB data file was obtained and condensed to only include stage IV A/B anaplastic thyroid cancer cases during the years 2004 to 2018. Patients were selected based on histologic features of tumors, grade and stage of tumors, whether patients received surgery followed by radiation, whether their radiation treatment commenced at least 14 days after their surgery, and whether the RT total dose was between 4500 to 7680 cGy. The surgery to RT start interval (SRI) was calculated for all patients. Kaplan Meier survival curves for OS were evaluated based on the following ten groups of SRI intervals: 14-19 days, 20-23 days, 24-27 days, 28-31 days, 32-34 days, 35-37 days, 38-42 days, 43-49 days, 50-62 days, and greater than 62 days. Each of these groups of patients contained equal numbers of patients. Univariate comparisons were conducted followed by multivariate Cox regression, which included the following covariate variables: presence or absence of chemotherapy regimen in treatment plan, total thyroidectomy or alternate surgery, total dose of radiation, post-surgery margin status, Charlson-Deyo comorbidity score, tumor stage, age, and sex. Subsequently, hazard ratios for survival were calculated for ten SRI’s with equal numbers of patients based on the Cox regression. Results: The analysis included 444 patients after exclusions that were made as above. The mean age was 66 years old. The most common surgery was a total thyroidectomy (294 patients; 66.2% of patients). There were 353 (79.5%) patients who received chemotherapy with radiation. The median SRI was 34.0 days. The cohort of patients included 246 female patients (55.4%). Kaplan Meier analyses revealed that patients who received radiation between 14-19 days of surgery had a significantly reduced survival compared to most of the other SRI groups. On both univariate and multivariate analysis, there was a trend that indicated increased survival amongst patients in the 38-42 days SRI group as this group in both analyses had the lowest hazard ratios for death (Univariate HR: 0.491 (p=0.004); Multivariate HR: 0.518 (p=0.010)) of any SRI group when the 14-19 day SRI group served as the reference category. Discussion: Within the limitations of our retrospective study, it appears that delayed start of adjuvant radiation beyond NCCN recommendations is not necessarily detrimental to OS. Further prospective analyses may be necessary to identify the ideal timing of adjuvant radiation therapy. Citation Format: Andrew B. Bonner, Herbert Chen, Sharon A. Spencer, Christopher D. Willey, Adam J. Kole. The effect of timing of post-operative radiation on outcomes in anaplastic thyroid cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PO-056.