Rising incidence of second cancers in patients with low-risk (T1N0) thyroid cancer who receive radioactive iodine therapy.

The objective of this study was to evaluate patterns of RAI use and elevated risk of secondary primary malignancies (SPM) in patients with low-risk (T1N0) WDTC.

The Surveillance, Epidemiology, and End Results (SEER) database was used to analyze trends in RAI use over time in the United States. To determine the excess risk of secondary primary malignancies (SPM) the standardized incidence ratio (SIR) and excess absolute risk (EAR) of various cancers were calculated in the 2 cohorts.
Between 1973 and 2007, 37,176 patients with WDTC were followed in the SEER Program, equating to 408,750 person-years at risk (PYR). In total, 14,589 patients received RAI, and SPMs were observed in 3223 patients.

RESULTS:

• During the study period, the rate of RAI use in patients with low-risk (T1N0) WDTC increased from 3.3% to 38.1%.
  
• or low-risk patients, the SIR of SPM was 1.21 (95% confidence interval [CI], 0.93-1.54), and the EAR was 4.6 excess cases per 10,000 PYR.
  
• SPM with significantly elevated risk because of RAI were salivary gland malignancies (SIR = 11.13; 95% CI, 1.35-40.2) and leukemia (SIR = 5.68; 95% CI, 2.09-12.37).
  
• The excess risk of leukemia was significantly greater in patients aged <45 years (SIR = 5.32; 95% CI, 2.75-9.30) compared with the excess risk in older patients (SIR = 2.26; 95% CI, 1.43-3.39).

CONCLUSIONS:

• The increased risk of a SPM in patients with low-risk (T1N0) WDTC, along with a lack of data demonstrating improved survival outcomes with adjuvant RAI, provide a compelling argument in favor of rationing the use of RAI in this patient population. Cancer 2011;. © 2011 American Cancer Society.

Cancer. 2011 Mar 22. doi: 10.1002/cncr.26070. [Epub ahead of print]