The risk of multiple primary breast and thyroid carcinomas

Area of Science:

• Oncology
• Radiation Oncology
• Epidemiology

Background:

• Studies suggest an association between breast and thyroid carcinomas.
• Ionizing radiation is a known risk factor for both breast and thyroid cancers.

Purpose of the Study:

• To investigate the effect of radiation dose from treating one cancer on the risk of developing the other.
• To analyze the risk of subsequent thyroid carcinoma after breast carcinoma treatment.
• To examine the risk of subsequent breast carcinoma after thyroid carcinoma treatment.

Main Methods:

• Retrospective cohort study analyzing 7,711 women treated for breast carcinoma and 2,365 women treated for thyroid carcinoma.
• Matched case-control analysis for thyroid carcinoma risk after breast carcinoma treatment.
• Cohort analysis for breast carcinoma risk after thyroid carcinoma treatment, considering radiation doses (Gy).

Main Results:

• Radiation therapy for breast carcinoma did not elevate the risk of subsequent thyroid carcinoma (Relative Risk = 1.2).
• No significant relationship was found between radiation dose and thyroid carcinoma risk (P = 0.8).
• An increased incidence of breast carcinoma was observed in women younger than 59 treated for thyroid carcinoma, but this was not linked to radiation dose (mean 0.7 Gy).

Conclusions:

• The previously observed excess of breast carcinoma after thyroid carcinoma treatment is not attributable to (131)I or external radiation therapy.
• Radiation therapy for breast carcinoma does not appear to increase the risk of developing thyroid carcinoma.