Course and Predictive Factors of Incomplete Response to Therapy in Low- and Intermediate-Risk Thyroid Cancer

CONTEXT: Controversy surrounds the extent and intensity of the management of American Thyroid Association (ATA) intermediate- and low-risk patients with differentiated thyroid cancer (DTC). Understanding the natural history and factors that predict outcome is important for properly tailoring the management of these patients. OBJECTIVE: This work aims to study the natural course and predictive factors of incomplete response to therapy in low- and intermediate-risk DTC. PATIENTS AND METHODS: We studied a cohort of 506 consecutive patients [418 women (82.6%) and 88 men (17.4%)] with low and intermediate risk with a median age of 35 years (interquartile range [IQR], 27-46 years). We analyzed the natural course and the predictive factors of biochemically or structurally incomplete response. RESULTS: Of 506 patients studied, 297 (58.7%) patients were in the low-risk group and 209 (41.3%) were in the intermediate-risk group. Over a median follow-up of 102 months (IQR, 66-130 months), 458 (90.5%) patients achieved an excellent response, 17 (3.4%) had a biochemically incomplete status, and 31 (6.1%) had a structurally incomplete status. In univariable and multivariable analyses, age (≥ 33 years) (P < .0001, odds ratio 1.06 [1.04-1.08]) and lateral lymph node metastasis (LNM; P < .0001, odds ratio 3.2 [1.7-5.9]) were strong predictive factors for biochemically and structurally incomplete response to therapy. Sex, tumor size, multifocality, extrathyroidal extension, and lymphovascular invasion did not predict incomplete response to therapy. CONCLUSIONS: Patients with low- and intermediate-risk DTC have favorable outcomes. Age and lateral LNM are strong predictors of an incomplete response to therapy. This suggests that older patients and those with LNM should be managed and followed up more actively than younger patients and those without LNM.