THE EFFECTS OF SURGERY, RADIOIODINE, AND EXTERNAL RADIATION-THERAPY ON THE CLINICAL OUTCOME OF PATIENTS WITH DIFFERENTIATED THYROID-CARCINOMA

BACKGROUND. The aim of this study was to determine the prognostic fact ors for local failure and cause specific survival in differentiated th yroid carcinoma and the impact of surgery, radioiodine, and external b eam radiation therapy (RT) when used as part of the initial management . METHODS. The authors reviewed the records of 382 patients with diffe rentiated thyroid carcinoma (papillary, 262; follicular, 120) managed at the Princess Margaret Hospital (PMH) between 1958 and 1985. There w ere 220 patients with Stage I or II, 102 with Stage III, and 33 with S tage IV disease (according to 1987 staging criteria of the Internation al Union Against Cancer). The median duration of follow-up was 10.8 ye ars. Potentially important prognostic factors for cause specific survi val (CSS) and local relapse free rate (LRFR) were tested by multivaria te regression analysis with emphasis on treatment factors. RESULTS. Fo r patients with papillary tumors, the 10-year CSS and overall survival were 93% and 85%, respectively; for those with follicular tumors, the y were 69% and 56%. The LRFR for both histologic types were 86% at 10 and 15 years. Age >60 years, tumor size >4 cm, poor differentiation, p ostoperative presence of macroscopic residual disease, and presence of distant metastasis at presentation were identified in multivariate an alysis as statistically significant factors for cause specific death. Age >60, tumor size >4 cm, multifocality, postoperative residuum, lymp h node involvement, less extensive surgery (less than near-total thyro idectomy), and the lack of use of radioiodine were significant with re gard to locoregional failure. The use of external RT was associated wi th more advanced local disease. There were no statistically significan t differences in CSS or LRFR between patients who received RT and thos e who did not, even after adjustment for identified prognostic factors . In the subgroup of 155 patients with papillary histology and microsc opic residuum, both 10-year CSS (100% vs. 95%, P = 0.038) and LRFR (93 % vs. 78%, P = 0.01) were higher for patients given RT than for those not given RT. The 33 patients with macroscopic residual disease who re ceived postoperative RT had a 5-year LRFR of 62% and CSS of 65%. CONCL USIONS. The prognostic factors for differentiated thyroid carcinoma ha ve been clearly identified. Initial total thyroid ablation with total thyroidectomy and radioiodine was associated with a lower rate of loca l relapse, although CSS was unaffected. Many patients at risk for loca l recurrence received postoperative RT, which did not significantly af fect the risk of local relapse or CSS in the entire group. A beneficia l effect of RT was demonstrated in the subgroup of patients with papil lary tumors and microscopic residuum. Patients with postoperative macr oscopic residual disease appeared to benefit from RT (with or without radioiodine). A Phase III trial involving patients at high risk for lo cal recurrence is required to assess the potential benefit of RT. (C) 1998 American Cancer Society.