Women with breast cancer treated with radiotherapy using tangential fields – where radiation is directed at an angle to the breast – after lumpectomy show increased risk of cancer in the other breast, with an even higher risk in younger women and in those with family members who have had breast cancer.

Women who have had breast cancer have a three to four times higher risk of developing a new primary cancer in their other breast (contralateral breast cancer), compared with the risk of a first primary breast cancer in other women. This increased risk could be due to a common cause for the tumours in both breasts, such as a genetic tendency or hormonal risk factors.

Few studies have looked at whether modern radiotherapy and chemotherapy affect this risk, so a large study was carried out to assess the long-term risk of contralateral breast cancer in young women, focusing on the effects of radiation dose, chemotherapy and their family history of breast cancer.

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The study included 7,221 predominantly young women treated for breast cancer at two centres in the Netherlands between 1970 and 1986. The researchers searched the patients’ records for information on the treatment for their primary cancers (surgery, radiotherapy, chemotherapy and hormonal), whether they suffered recurrent cancer and their family history of breast cancer.

Results showed that radiotherapy did not significantly increase the risk of contralateral breast cancer overall. However, the risk associated with radiotherapy was higher in younger women. Those younger than 35 years at first treatment had nearly twice the risk of breast cancer associated with radiotherapy in the other breast (HR 1.78; 95% CI, 0.85-3.72) compared to women over 45 years (HR 1.09; 95% CI, 0.82-1.45).

The risk of contralateral breast cancer also depended on the type of radiotherapy, which was determined by the location and stage of the primary cancer. Women treated before the age of 45 years with radiotherapy after lumpectomy showed a 1.5-fold increased risk of cancer in their other breast compared with those who had radiotherapy after mastectomy.

The researchers suggested that the difference might have occurred because post-mastectomy radiotherapy using direct electron fields led to a significantly lower radiation exposure to the contralateral breast than post-lumpectomy radiotherapy using tangential fields.

Treatment with adjuvant chemotherapy (cyclophosphamide, methotrexate and fluorouracil) was associated with a non-significantly decreased risk of contralateral breast cancer in the first five years of follow-up, but did not reduce the risk in subsequent years.

Hooning MJ, Aleman BMP, Hauptmann M et al. Roles of radiotherapy and chemotherapy in the development of contralateral breast cancer. J Clin Oncol 2008; 26: 5561-68. Summaries provided by the European School of Oncology’s Cancer Media Service

Originally published in the November 2008 edition of MIMS Oncology & Palliative Care.