Prognostic Factors Determining Long-Term Survival in Well-Differentiated Thyroid Cancer: An Analysis of Four Hundred Eighty-Four Patients Undergoing Therapy and Aftercare at the Same Institution

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Abstract
Objectives: Identification of the prognostic factors relevant for long-term survival in differentiated thyroid cancer in a homogenously treated patient cohort in order to allow a better initial risk stratification. Methods: Four hundred eighty-four (358 females/126 males) patients with differentiated thyroid cancer (330 papillary [68.2%]; 154 follicular [31.8%]) were included. Inclusion criteria consisted of treatment with a uniform therapy scheme and continuous aftercare in the same institution. Initial diagnosis was between 1975-1995 (age at diagnosis, 14-84 years, median, 49.7). Tumor stage: pT1, n = 92; pT2, 211; pT3, 58; pT4, 123. Low-risk: ≤pT3 NX M0, 331; high-risk pT4 and/or M1, 153. After thyroidectomy all patients had at least two 131I therapies (4-month interval; first, 2-4 GBq; second, 3.7-8 GBq). The median follow-up was 7.6 years (range, 0.2-23.9). The role of eight variables as prognostic factors was tested by regression analysis. Results: The corrected cause-specific 5-, 10-, and 20-year survival rates in the whole cohort were 0.95, 0.90, 0.83, respectively; for the low risk-category of papillary cancer, 0.99, 0.97, 0.89; for follicular cancer, 0.98, 0.89, 0.89 (difference papillary/follicular p = 0.0004). The cause-specific survival rates in the high-risk category of papillary cancer were 0.89, 0.85, and 0.85; for follicular cancer, 0.88, 0.73 and 0.52 (p = 0.0016). Variables with significant negative influence on survival were distant metastases, persisting elevated human thyroglobulin levels after one 131I therapy, age greater than 45 and gender in follicular cancer. Locoregional external radiotherapy did not improve survival but was associated with comorbidity. The aggressiveness of the initial operative resection was also not a prognostic factor for survival. pT4 NX M0 patients of our patient cohort did not exert significant differences in long-term survival compared to pT13 NX M0. This was also true for patients older than 45 years, where the 5- and 10-year survival rates for pT4 NX M0 were 0.93 and 0.90. Conclusion: Our therapy and aftercare strategy results in a high long-term survival rate especially for high-risk patients. In our patient sample radical initial lymph node resection did not extend long-term survival.