Radiotherapy has contralateral breast cancer risk only in certain women

MedWire News: Modern radiotherapy techniques for treating a primary breast cancer do not appear to increase a woman’s risk for developing a contralateral tumor, research shows.

However, young patients and those with a family history of the disease appear to be more sensitive to the carcinogenic effects, acting to increase contralateral breast cancer risk.

“This finding should be taken into account when advising breast radiation with tangential fields to young patients with breast cancer,” Flora van Leeuwen (the Netherlands Cancer Institute, Amsterdam) and colleagues comment in the Journal of Clinical Oncology.

Women with breast cancer have a three- to four-fold increased risk for developing a new primary cancer in the contralateral breast, compared with the risk for a first primary cancer among other women.

This excess risk can be largely explained by genetic predisposition and/or hormonal risk factors, although treatment-related causes may also play a role.

A study in 1992 estimated that 11% of all contralateral breast cancers in women who undergo radiotherapy before age 45 years could be attributed to radiation. However, the radiotherapy techniques evaluated in their study are no longer routinely used and more relevant data is needed.

For the current study, the researchers followed-up 7221 breast cancer survivors for a second contralateral tumor, focusing on the effects of radiation dose, chemotherapy, and family history of breast cancer.

After a median follow-up of 13.8 years, 503 contralateral breast cancers were observed, resulting in a significantly increased standardized incidence ratio of 2.91 compared with the general female population.

Multivariate cox model analysis revealed that radiotherapy did not significantly increase the risk for a contralateral breast cancer in the entire sample (hazard ratio [HR]=1.15).

In patients who underwent radiotherapy before aged 35 years, the HR for contralateral breast cancer was a significant 1.78, whereas for patients irradiated at age 45 years or older the risk decreased to a non-significant HR of 1.09.

Patients with three or more relatives with breast cancer experienced a 2.4-fold increased risk for contralateral breast cancer compared with patients with no affected relatives.

Treatment with adjuvant chemotherapy was associated with a nonsignificantly decreased risk for contralateral breast cancer in the first 5 years of follow-up, but did not reduce risk in subsequent years

“Further evaluation is needed of the increased risk of contralateral breast cancer from tangential breast fields overall and in BRCA1/2 mutation carriers in particular,” van Leeuwen and colleagues conclude.