Performance of ATA Risk Stratification Systems, Response to Therapy, and Outcome in an Indian Cohort of Differentiated Thyroid Carcinoma Patients: A Retrospective Study

Introduction: For better individualized management of differentiated thyroid carcinoma (DTC), ATA risk stratification systems (RSS) of 2009 and 2015 as well as a response to therapy re-classification (ATA RTR-2015) are used worldwide for assessing risk of recurrence. But there are no validation studies of these systems from the Indian subcontinent. Objectives: To compare ATA RSS-2009, ATA RSS-2015, and ATA RTR-2015 for their accuracy in predicting outcome in DTC patients. Methods: This was a retrospective review of 236 adult patients with DTC >1 cm attending the Thyroid Cancer Clinic at our Institute who had undergone total thyroidectomy and radioactive iodine ablation. Initial risk stratification using ATA RSS-2009 and RSS-2015, clinical response at 1 year and outcome at last follow-up measured by clinical end points were collected and analyzed. Results: ATA RSS-2015 could not be applied to this cohort due to lack of histopathology details. While 77.3% of low-risk ATA RSS-2009 had disease-free status (NED, no evidence of disease) on follow-up, 96.1% of patients, in excellent response in ATA RTR-2015, showed NED. Whereas persistent structural disease was predicted by the high-risk group in ATA RSS-2009 (61.9%) and by the incomplete structural response group in ATA RTR-2015 (57.1%) equally well, the best predictor for NED at 1 year in this cohort was ATA RTR-2015 (p < 0.001). Conclusion: This study found that both ATA RSS-2009 and ATA RTR-2015 are reliable in predicting outcome in DTC patients after initial treatment. However, the response to initial therapy at 1 year predicted outcome more accurately than the initial risk status.