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Cancer Epidemiol Biomarkers Prev. 2012 Jan;21(1):92-101. doi: 10.1158/1055-9965.EPI-11-0576. Epub 2011 Oct 25.

Chemotherapy and thyroid cancer risk: a report from the childhood cancer survivor study.

Author information

  • 1Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, 6120 Executive Boulevard EPS 7051, MSC 7238, Bethesda, MD 20892, USA. veigal@mail.nih.gov

Abstract

BACKGROUND:

Although ionizing radiation is an established environmental risk factor for thyroid cancer, the effect of chemotherapy drugs on thyroid cancer risk remains unclear. We evaluated the chemotherapy-related risk of thyroid cancer in childhood cancer survivors and the possible joint effects of chemotherapy and radiotherapy.

METHODS:

The study included 12,547 five-year survivors of childhood cancer diagnosed during 1970 through 1986. Chemotherapy and radiotherapy information was obtained from medical records, and radiation dose was estimated to the thyroid gland. Cumulative incidence and relative risks were calculated with life-table methods and Poisson regression. Chemotherapy-related risks were evaluated separately by categories of radiation dose.

RESULTS:

Histologically confirmed thyroid cancer occurred in 119 patients. Thirty years after the first childhood cancer treatment, the cumulative incidence of thyroid cancer was 1.3% (95% CI, 1.0-1.6) for females and 0.6% (0.4-0.8) for males. Among patients with thyroid radiation doses of 20 Gy or less, treatment with alkylating agents was associated with a significant 2.4-fold increased risk of thyroid cancer (95% CI, 1.3-4.5; P = 0.002). Chemotherapy risks decreased as radiation dose increased, with a significant decrease for patients treated with alkylating agents (P(trend) = 0.03). No chemotherapy-related risk was evident for thyroid radiation doses more than 20 Gy.

CONCLUSIONS:

Treatments with alkylating agents increased thyroid cancer risk, but only in the radiation dose range less than 20 Gy, in which cell sparing likely predominates over cell killing.

IMPACT:

Our study adds to the evidence for chemotherapy agent-specific increased risks of thyroid cancer, which to date, were mainly thought to be related to prior radiotherapy.

PMID:
22028399
[PubMed - indexed for MEDLINE]
PMCID:
PMC3253948
Free PMC Article

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