Radiation Treatment for Breast Cancer Causes Cancer in the Other Breast on Treatment for Breast Cancer Causes Cancer in the Other BreastYoung women who receive radiation treatment after breast cancer surgery are significantly more likely to later develop cancer in the other breast than women who did not undergo such radiation.
The findings come from a study, published online in the Journal of Clinical Oncology, on more than 7,000 women who were treated for breast cancer in Netherlands between the years of 1970 and 1986. All study participants were diagnosed with breast cancer before the age of 71.
Among study participants in general, the risk of developing cancer in the opposite breast (contralateral breast cancer) after treatment in the first breast was three to four times higher than the rate for new cases of breast cancer. This risk only went up with a number of other risk factors, including family predisposition or treatment with radiation or chemotherapy.
Researchers from the Erasmus Medical Center Daniel den Hoed Cancer Center in Rotterdam examined the cancer risk in women based on whether they were treated with radiation after a lumpectomy (partial breast removal) or mastectomy (complete breast removal). They found that women under the age of 45 who received radiation treatment after a lumpectomy were 1.5 times more likely to develop contralateral cancer than women who received post-mastectomy radiation treatment.
Similarly, the risk of contralateral breast cancer among all patients under the age of 45 increased by 9 percent if they had received radiation treatment. Among women treated before the age of 35, the increase in risk associated with radiation therapy was far higher — 78 percent.
When the participants were examined all together and not divided by age, there was no correlation between radiation treatment and increased cancer risk.
Radiation treatment is commonly used after the surgical removal of cancerous breast tissue in order to kill any cancerous cells that might remain. It is used most often after any lumpectomy, after any mastectomy of a breast that contained a tumor larger than five centimeters, or in any cancer that has spread to the lymph nodes.
The chemotherapy drugs cyclophosphamide, fluorouracil and methotrexate also increased the risk of contraleteral cancer, but only after five years. Within the first five years after treatment, there was no difference in contralateral cancer rates between those who had received the drugs and those who had not.
To date, many researchers have assumed that high rates of contralateral breast cancer can be mostly attributed to the risk factors that contributed to the original cancer, such as genetic predisposition. This study is one of the first to suggest that cancer treatment itself might also increase risk.
That family predisposition affects breast cancer risk is fairly well accepted by researchers, and scientists have identified two genetic mutations in particular (BRCA1 and BRCA2) that seem to play a role. In the current study, the highest risk of contralateral cancer was seen among women who had three or more relatives who had already had breast cancer. But such predispositions appear to have the greatest effect in the presence of environmental risk factors.
In the current study, young women who had received post-lumpectomy radiation treatment and who also had a strong history of breast cancer in their family had their risk of contralateral cancer increased by 3.5 times.