Outcomes of patients with low-risk differentiated thyroid cancer with an excellent response to initial therapy.

OBJECTIVE: Patients with differentiated thyroid carcinoma (DTC) classified as low risk of recurrence and an excellent response to initial treatment should have a particularly low risk of recurrence. Our objective was to assess the recurrence rate in these patients to support follow-up de-escalation. METHODS: A multicentre retrospective study was conducted in six Spanish hospitals, including consecutive patients diagnosed with low-risk DTC between 2015 and 2018 with an excellent response to initial therapy. RESULTS: A total of 379 patients were included, with a median follow-up of 6.7 years. Response to therapy at last follow up, according to the 2015 ATA/Momesso criteria was excellent in 349 patients (92.1%), indeterminate in 29 (7.6%), and biochemically incomplete in 1 (0.3%). The overall incidence of indeterminate response was 11.8 events per 1,000 person-years, peaking at year three of follow-up and dropping to near zero after year seven. PTC and RAI treatment were associated with a lower probability of developing an indeterminate response (p=0.02 and p=0.03, respectively). When applying the 2025 ATA criteria, the excellent response rate increased to 95.8% and neither papillary histology nor RAI treatment were significantly associated (p=0.07 and p=0.61, respectively). During follow up, indeterminate/suspicious findings on ultrasound were observed in 39 patients (10.3%). FNA was performed in 20 of these, none of which found recurrence. CONCLUSIONS: Recurrences in patients with low risk of recurrence and an excellent response to initial therapy are extremely infrequent. These data support follow-up de-escalation in this population.