The role of adjuvant external beam radiotherapy (EBRT) in differenciated thyroid cancer (DTC) is controversial. It remains unknown whether EBRT in the neck following conventional treatment might improve progression-free survival (PFS) and overall survival (OS).
Objective: To assess EBRT outcomes in patients with locally advanced DTC in terms of local disease progression, PFS and OS.
Material and Methods: A multicentric retrospective study was performed including all those patients diagnosed of DTC and treated with EBRT in the neck or mediastinum as a consequence of incomplete resection, extrathyroidal extension (ETE) and/or local recurrence after surgery. Quantitative variables expressed as median [interquartile range].
Results: Sixty-seven patients (48 women; age at diagnosis 62  years) from 11 different hospitals in Spain were included. 32.3% (n=23) of cases had an aggressive histologic variant. 75.8% (n=50) of tumours had the resection margins involved, 86.4% (n=57) had ETE and extranodal extension was present in 43.8% (n=28). Iodine-refractory patients were 73.8% (n=48). Age at EBRT time was 68  years. Radiotherapy was administered mainly in the neck (74.6%), followed by neck and mediastinum (22.4%). Conventional EBRT was used in 38.6% of patients, followed by IMRT (35.1%) and 3DRT (19.3%). The median dose was 60  Gy. Indications of EBRT were ETE in 50.7%, disease persistence/recurrence after surgery (34.3%), extranodal extension and high-risk histology (7.5% each one). The median follow-up period after EBRT was 41  months. Thyroglobulin decreased or stabilized in 84.6% of patients without distant metastases during the follow-up. In this group (M0, n=39) radiotherapy stabilized or reduced structural local disease in 96.8%, 96% and 92.9% at 1, 2 and 5 years, respectively. In M1 patients (n=25), EBRT stabilized or reduced cervical/mediastinal disease in 64.3%, 56.2%, 50% at 1, 2 and 5 years. OS rate was 68.7% (mean OS 10.9 years; CI 95%, 8.812.9). EBRT dose ≥60 Gy was associated with an increase in mean OS compared with dose <60Gy (11.2 vs 6.9 years, P=0.01). Patients <55 years had longer mean OS than those ≥55 years (15.7 vs 7.2 years, P=0.004). The location of EBRT (neck or mediastinum) was associated with different means of OS. Type of histology or positive surgical margins were also related with different mean PFS.
Conclusions: In our experience, adjuvant EBRT was useful to control local disease in aggressive DTC. Location of therapy (neck), age <55 and EBRT dose ≥60 Gy could be predictors of better clinical response to treatment.
18 - 21 May 2019
European Society of Endocrinology