Efficacy of stereotactic radiotherapy in patients with oligometastatic iodinerefractory thyroid cancer.

Differentiated thyroid cancer is usually associated with a good prognosis. The development of metastases in Iodine-refractory thyroid cancer adversely affect patients’ quality of life and survival. The advent of tyrosine-kinase inhibitors drugs (TKI) allowed a great improvement of patients’ outcome but, in case of oligometastatic disease, a locoregional ablative approach such as Stereotactic Radiation Therapy (SRT) could effectively control tumour progression and possibly defer the need of systemic therapies. In our study, we analysed the effectiveness of SRT in oligometastatic Iodine-refractory thyroid cancer patients. Methods: We retrospectively analysed patients with differentiated oligometastatic thyroid cancer treated with SRT in our Radiation Oncology Unit from 2011 to 2020. We collected demographics and treatment-related characteristics. Local Control (LC), Progression Free Survival (PFS) and Overall Survival (OS) rates were evaluated. Patients with anaplastic histology, incomplete treatment or without follow-up information were excluded. Results: We retrospective analysed a cohort of 15 patients, aged between 47 and 72 years old (median 63,3). 8 (53,3%) patients were males and 7 (46,7%) were females. A total of 42 lesions were treated: 19 were located in bones (45,2%), 11 in lymph nodes (26,2%), 3 visceral (7.1%), 7 in the brain (16,7%) and 2 in the lungs (4,8%). SBRT was delivered in 1-8 fractions, with a median dose of 30Gy (range 14-60Gy). Median followup from the date of the first SRT was 47,7 months (range 14,4–105 months). After SRT we observed a complete response in 21 lesions (50%), partial response in 13 (31%), stable disease in 7 (16,7%) and only 1 progressive lesion (2,4%). We observed 9 local recurrences (21,4%) with an actuarial LC of 95% and 89,9% at 12 and 24 months respectively, while PFS was 45.6% and 32,9% at 12 and 24 months respectively. The OS at 12, 24, 48 months was 93,3%, 86,2% and 79%, respectively. A total number of 10 patients (66,7%) underwent TKI treatment (4 Sunitinib and 5 Lenvatinib) for progressive disease: median time to first systemic treatment from the SBRT was 17,7 months (range 1-47,7 months). At the end of this analysis, 5 patients (33.3%) were still without systemic therapy, showing a good disease control after a median follow-up of 50,6 months (range 35.3-57). Conclusions: In our experience, SRT yields satisfying local control rates in oligometastatic Iodine-refractory thyroid cancer, allowing for a deferral of systemic therapies. [ABSTRACT FROM AUTHOR]