Spontaneous remission in thyroid cancer patients after biochemical incomplete response to initial therapy

Summary Objective To validate the A merican T hyroid A ssociation ( ATA ) initial risk of recurrence scheme and the M emorial S loan K ettering C ancer C enter ( MSKCC ) response to therapy re‐stratification approach in a large cohort of patients with differentiated thyroid cancer ( DTC ) treated outside of the U nited S tates. Design Retrospective chart review. Patients Five hundred and six patients with DTC followed for a median of 10 years after total thyroidectomy and RAI remnant ablation at a major cancer centre in B razil. Measurements Final clinical outcomes were assessed based on A merican J oint C ancer C ommittee ( AJCC )/ U nion I nternationale C ontre le C ancer ( UICC ) staging, ATA risk stratification and response to therapy assessment (excellent, acceptable, biochemical incomplete and structural incomplete). Results The AJCC / UICC staging system did not adequately stratify patients with regard to the risk of recurrence/persistent disease. However, the ATA system demonstrated a 13% risk of recurrent/persistent disease in low‐risk patients, 36% in intermediate risk patients, and 68% in high‐risk patients. Furthermore, an excellent response to therapy decreased the risk of recurrent/persistent disease to 1·4%. At the time of final follow‐up, 34% of the biochemical incomplete response patients had been re‐classified as having no evidence of disease ( NED ) without having received any additional therapy beyond continue levothyroxine suppression. Conversely, even after additional therapies, only 9% of the patients with an incomplete structural response were eventually re‐classified as NED . Conclusions These data validate the ATA risk classification as an excellent initial predictor of recurrent/persistent disease and confirm the clinical utility of the MSKCC dynamic risk assessment system in a cohort of patients evaluated and treated outside the U nited S tates.