The effect of timing of post-operative radiation on outcomes in anaplastic thyroid cancer.

backgroundAnaplastic 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 (PORT). 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 practice patterns with regard to PORT timing, and to assess whether the time interval between surgery and the start of RT impacts overall survival (OS).

methodsAn NCDB data file was obtained and condensed to only include stage IVa and IVb anaplastic thyroid cancer cases during the years 2004 to 2018. Patients were included if they were treated with surgery followed by radiation (6000 cGy-7020 cGy), and the radiation commenced no later than 90 days after surgery. Patients were grouped according to PORT: Early PORT (≤ 21 days after surgery) and Late PORT (> 21 days after surgery). Several variables were tested using univariate and multivariate binary logistic regression to determine their effect on whether patients received Early PORT vs. Late PORT. These variables were also used to conduct univariate and multivariate Cox regression to determine effects on survival for the cohort. The covariate variables included: presence or absence of a chemotherapy regimen in the treatment plan, total thyroidectomy or alternate surgery, type of treatment facility (Academic vs. Other), resection margin status (R0/R1 vs. R2), Charlson-Deyo comorbidity score, tumor stage, age, race/ethnicity and sex.

resultsThe analysis included 277 patients after exclusions. The Early PORT group included 57 patients, and the Late PORT group included 220 patients. Multivariate binary logistic regression analysis showed that patients with R2 resection margins were less likely to receive Late PORT compared to patients with R0/R1 resection margins (OR: 0.306 (0.123–0.764)), and patients with stage IVb disease were less likely to receive Late PORT compared to patients with stage IVa disease (OR: 0.496 (0.257–0.957)). Multivariate cox regression analysis displayed survival advantages for patients who received Late PORT (HR: 0.563 (0.401–0.790)) and patients with R0/R1 resection margins (HR: 1.901 (1.161–3.114)), while treatment at an academic center trended toward significance (p = 0.053). DISCUSSION: The majority of patients in this cohort received Late PORT, later than the proposed guidance by the NCCN. Resection margin status and disease stage appears to influence how physicians select the timing of PORT. Within the limitations of our retrospective study, delayed PORT beyond NCCN recommendations is not associated with a detriment to OS. Further prospective analyses may be necessary to identify the ideal timing of adjuvant radiation therapy.