Intermediate-Risk Papillary Thyroid Cancer: Risk Factors for Early Recurrence in Patients with Excellent Response to Initial Therapy.

BACKGROUND: Patients with excellent response to initial therapy have a low rate of tumor recurrence. The objectives of this study were to evaluate the rate of early tumor recurrence in patients with intermediate-risk papillary thyroid cancer who had an excellent response to initial treatment and to identify risk factors.

METHODS: This retrospective cohort study included 217 patients with American Thyroid Association intermediate-risk papillary thyroid cancer who had a documented excellent response to initial treatment (total thyroidectomy and adjuvant therapy with 100-150 mCi [3.7-5.5 GBq] of radioactive iodine [RAI]). The assessed outcome was recurrence, defined as new evidence of disease after any disease-free period. Multivariate logistic regression and Cox regression models were used to determine the factors associated with recurrence upon recording clinical, surgical, and pathology variables.

RESULTS: Sixteen (7.4%) cases of recurrent disease were documented after a median follow-up period of 42 months (range 17-88 months). Structural recurrence was documented in 10 (62.5%) patients, and biochemical recurrence was documented in the remaining six patients. The logistic regression model identified a significant association between early recurrence and pN1b involvement (odds ratio [OR] = 10.81 [confidence interval (CI) 1.87-62.59]), lateral neck RAI uptake (OR = 6.06 [CI 1.67-22]), and pre-ablation thyroglobulin >10 ng/mL (OR = 4.01 [CI 1.16-13.85]). Variables that proved significant in the Cox regression model were: pN1b involvement (hazard ratio = 9.6 [CI 1.91-48.52]) and lateral neck RAI uptake (hazard ratio = 5.95 [CI 1.86-18.97]).

CONCLUSION: The observed early recurrence rate of 7.4% is uncharacteristically high for a population of patients who had an excellent response to initial treatment. The significant association that was found between recurrent disease and lateral neck lymph node metastasis, lateral neck I131 uptake in post-therapy whole-body scan, and pre-ablation thyroglobulin levels >10 ng/mL indicates that early recurrence (<5 years) most likely indicates progression of micrometastatic disease already present at diagnosis and unsuccessfully eradicated with initial therapy.