Clinical outcomes of adjuvant external-beam radiotherapy for differentiated thyroid cancer - results after 874 patient-years of follow-up in the MSDS-trial.

AIM Evaluate the clinical benefit of external beam radiotherapy (RTx) for locally invasive thyroid carcinoma with follicular cell differentiation (DTC). PATIENTS, METHODS The Multicentre Study on Differentiated Thyroid Cancer (MSDS) was planned as a prospective multicenter trial on the benefit of adjuvant RTx in locally invasive DTC (pT4; UICC 1997) with or without lymph node metastases and no known distant metastases. All patients were treated with thyroidectomy, 131I-therapy, and TSH-suppression and were randomized to receive additional RTx or not. In 4/2003 the trial became a prospective cohort study after only 45 of then 311 patients had consented to randomization. 351 of 422 patients met the trial's inclusion criteria. Age was 48 +/- 12 years (mean +/- SD). 25% were men. Tumours were papillary in 90% and follicular in 10%. Of 47 patients randomized or allocated to RTx, 26 actually received RTx. RESULTS Mean follow-up was 930 days. In an actual treatment analysis, 96% (25/26) of the RTx-patients reached complete remission (CR) vs. 86% in the non-RTx patients. Recurrences occurred in 0 vs. 3 % of patients: 6 reoperated for regional lymph node metastases, 1 tracheal invasion treated with tracheoplasty, 1 local invasion necessitating laryngectomy, 2 distant metastases (1 lung, 1 lung + bone). Serious chronic RTx toxicity occurred in 1/26 patients. CONCLUSION The MSDS trial showed low mortality and recurrence rates and a weak benefit of RTx in terms of local control that did however not reach statistical significance. Routine RTx in locally invasive DTC can no longer be recommended.