Long-Term Follow-Up of Differentiated Thyroid Carcinoma in a Specialized Oncological Center: Impact of Radioiodine Therapy

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Introduction: Thyroid cancer is the most frequent endocrine malignancy, representing the fourth most common neoplasia in Mexico. Differentiated thyroid cancer (DTC) has generally a good overall prognosis, with a very low cancer specific mortality (< 5% at 10 years). Treatment consists mainly in surgery, followed by radioiodine therapy. The main objective of this study is to assess the impact of radioiodine therapy in overall survival (OS) and disease-free survival (DFS) in patients with DTC, and whether accumulated ¹³¹I activity (RAA) is associated with long-term follow-up thyroglobulin (Tg) levels. Secondary objective was to establish if histopathological risk factors have a statistically significant association with recurrent, persistent, and metastatic disease.

Methods: We conducted a single center (Instituto Nacional de Cancerología, México), nonrandomized, ambispective cohort study, where 50 patients with DTC were followed up through 15 years since diagnosis, from January 2007 to February 2023. SPSS V24.0 was used for statistical analysis. X2 test was used for parametric data, and Kruskal–Wallis test for nonparametric data.

Results: Twenty-eight percent out of the 50 patients (72% woman, 28% man; mean age at diagnosis 44.5 ± 17 years) had died at the end of the follow-up period. Mean overall survival was 11.5 years, and disease-free survival was 4.3 years. Furthermore, in the overall survival analysis, patients with RAA between 5,550 and less than 11,100 MBq and those that received 11,100 MBq or more had an OS of 12.5 years and 9.7 years, respectively. All of the patients were divided according to RAA and serum Tg measures at two points in time: postsurgical and last sample taken, which was further classified into negative, undetermined, and elevated: median RAA was 4,995, 4,625, and 11,470 MBq for each postsurgical Tg group respectively (p = 0.036), while RAA regarding last Tg measures was 6,160.5, 8,325, and 13,616 MBq (p = 0.231). Histopathological risk factors (extra-thyroid extension, incomplete resection, lymphovascular and perineural invasion, and osseous metaplasia) had a higher frequency association with persistent disease rather than recurrent or metastatic pathology (p = 0.087, 0.989, and 0.175, respectively).

Conclusion: Mexican population has higher death rates as well as lower OS and DFS in patients with DTC than those currently reported worldwide. A ≥ 11,100 MBq accumulated ¹³¹I activity was linked to a significantly lower than mean OS, possibly due to distant metastatic disease. RAA has statistically significant difference according to postsurgical Tg measure. Histopathological risk factors have higher frequency association in our population not with carcinoma recurrence as stated in some international guidelines, but rather with persistent disease overtime.

Publication History

Article published online:
25 May 2023