Abstract
The National Thyroid Cancer Treatment Cooperative Study Group (NTCTCSG) follows a cohort of patients with differentiated thyroid cancer (1 –5). In 2006, we reported the findings from our analysis of 2936 patients enrolled in our registry through 2001 (4). At that time, our median length of follow-up was 3 years, and 10,994 patient-years of follow-up were included. We have maintained our registry and as of 2010, we have accrued 4767 patients. We have considerably increased our median length of follow-up to 5.3 years and now have 29,693 patient-years contained within our database. With the benefit of the longer follow-up period, there is one previously reported finding that no longer holds true.
The specific finding that is no longer supported by our current data concerns the effect of radioiodine therapy in patients with stage I disease, as defined by the NTCTCSG staging system (2). This staging system differs from the American Joint Committee on Cancer (AJCC) system in that some patients with AJCC stage I disease are advanced to higher stages with our staging system. We feel it is imperative to report this revised conclusion, because it affects treatment considerations for approximately 50% of patients with differentiated thyroid cancer. Our 2006 report appeared to show an adverse effect on overall survival associated with radioiodine therapy in patients with stage I disease, despite the fact that the cause of these deaths appeared unrelated to thyroid cancer. In contrast, our 2010 analysis shows no association between radioiodine therapy and overall survival in this group (p-value 0.15 in univariate analyses; p-value 0.71 in multivariate analyses). Thus, in our present analyses, the effect of radioiodine therapy on patients with NTCTCSG-defined stage I disease is neutral and not associated with either an increase or decrease in survival. The implication of this finding is that if radioiodine therapy is deemed appropriate to improve accuracy of follow-up by thyroglobulin monitoring and radioiodine scanning in certain patients with stage I, our current findings show no detrimental effect of adjuvant radioiodine therapy on patient survival.
Our current analyses, and other annual analyses subsequent to 2006, consistently and reliably confirm the other findings we reported in 2006 (4).