THYROTROPIN SUPPRESSION AND DISEASE PROGRESSION IN PATIENTS WITH DIFFERENTIATED THYROID-CANCER - RESULTS FROM THE NATIONAL THYROID-CANCER TREATMENT COOPERATIVE REGISTRY

The ideal therapy for differentiated thyroid cancer is uncertain. Alth ough thyroid hormone treatment is pivotal, the degree of thyrotropin ( TSH) suppression that is required to prevent recurrences has not been studied in detail. We have examined the relation of TSH suppression to baseline disease characteristics and to the likelihood of disease pro gression in a cohort of thyroid cancer patients who have been followed in a multicenter thyroid cancer registry that was established in 1986 . The present study describes 617 patients with papillary and 66 patie nts with follicular thyroid cancer followed annually for a median of 4 .5 years (range 1-8.6 years). Cancer staging was assessed using a stag ing scheme developed and validated by the registry. Cancer status was defined as no residual disease; progressive disease at any follow-up t ime; or death from thyroid cancer. A mean TSH score was calculated for each patient by averaging all available TSH determinations, where 1 = undetectable TSH; 2 = subnormal TSH; 3 = normal TSH; and 4 = elevated TSH. Patients were also grouped by their TSH scores: group 1: mean TS H score 1.0-1.99; group 2: mean TSH score 2.0-2.99; group 3: mean TSH score 3.0-4.0. The degree of TSH suppression did not differ between pa pillary and follicular thyroid cancer patients. However, TSH suppressi on was greater in papillary cancer patients who were initially classif ied as being at higher risk for recurrence. This was not the case for follicular cancer patients, where TSH suppression was similar for ail patients. For all stages of papillary cancer, a Cox proportional hazar ds model showed that disease stage, patient age, and radioiodine thera py all predicted disease progression, but TSH score category did not. However, TSH score category was an independent predictor of disease pr ogression in high risk patients (p = 0.03), but was no longer signific ant when radioiodine therapy was included in the model (p = 0.09). The re were too few patients with follicular cancer for multivariate analy sis. These data suggest that physicians use greater degrees of TSH sup pression in higher risk papillary cancer patients. Our data do not sup port the concept that greater degrees of TSH suppression are required to prevent disease progression in low-risk patients, but this possibil ity remains in high-risk patients. Additional studies with more patien ts and longer follow-up may provide the answer to this important quest ion.