These women were part of a large longitudinal cohort study called the Childhood Cancer Survivor Study that enrolled women who had been diagnosed with a childhood cancer between 1970 and 1986 at one of 26 different institutions in North America and then had survived at least five years after their childhood cancer diagnosis. We looked at these women to look at the risk of breast cancer by just overall, by their childhood cancer diagnosis and by different doses and fields of radiation. We found that women who were treated with chest radiation have an increased risk of breast cancer; this is not new, multiple studies have shown this before but what we did show that other studies haven’t really focussed on so much is that this risk was not restricted to Hodgkin’s lymphoma survivors. Most of the previous work that has been done in this area has focussed on Hodgkin’s lymphoma survivors who were treated with very large doses of radiation to large areas of their chest but we’ve found that it’s not just the Hodgkin’s lymphoma survivors who are at increased risk of breast cancer, that this can include survivors of other childhood cancers as well who are also treated with different doses and different fields of radiation.
Current screening guidelines in the United States, the standard of care is the Children’s Oncology Group guidelines, breast cancer surveillance guidelines, and they recommend annual screening for women who were treated with at least 20Gy of radiation to the chest. We found that women who were treated with doses that are less than 20Gy also have an increased risk of breast cancer and the current guidelines do not recommend screening for these women, at least in the United States and Canada.
Is this found only in breast cancer?
We focussed exclusively here on women who were treated with radiation to the chest. It’s possible if they were treated with radiation to other areas that did not include breast tissue that they might also have an increased risk from the scatter radiation but we did not look at that. We focussed exclusively on the women for whom it was clear they were treated with radiation to the chest that involved some level of breast tissue exposure.
What is the increased risk?
Overall, for the whole chest irradiated cohort that we looked at, by age 50 we found a cumulative risk of breast cancer was 26%. It differs, though, by childhood cancer diagnosis primarily because the Hodgkin’s lymphoma survivors were treated with higher doses to larger areas. So by age 50 we found that for the Hodgkin’s lymphoma survivors their cumulative risk of breast cancer is 31%. So it’s essentially saying 31% of Hodgkin’s lymphoma survivors who were treated with radiation are getting breast cancer by the time they are 50 years old.
We looked at women who were not childhood cancer survivors but who had been diagnosed with breast cancer and they were part of an entirely different study called the WECARE study, the Women’s Environmental Cancer and Radiation Epidemiology study. We used that data to produce population based estimates of breast cancer risk in women who are carriers of either a BRCA1 or a BRCA2 gene mutation and we found that the risk of breast cancer in Hodgkin’s lymphoma survivors is very similar to the risk of breast cancer in women who are BRCA1 carriers, so one of the highest known risk populations. We also found that women who were treated with radiation to the chest for other childhood cancers besides Hodgkin’s lymphoma had a risk of breast cancer that was very similar to women who are carriers of BRCA2 gene mutations.
What are your recommendations for these women?
These women should be talking to their doctors, hopefully they should know something about their radiation treatment. If they don’t have medical records or radiation treatment summary from the time they were treated as children they should try to get it and bring it to their primary care doctors. They should be undergoing screening, they should be potentially at high risk clinics similar to how we handle women who are carriers of BRCA mutations.
Should they avoid mammograms?
That’s a great question. The amount of radiation exposure that comes with a mammogram is so miniscule compared to the amount of radiation that these women were already exposed to that the current thinking is that it’s not contributing that much excess risk. Further, it also somewhat depends upon the age so current studies that have looked at radiation exposure and how it contributes to breast cancer risk have shown that this increased risk comes primarily to women who are treated as children, adolescents or young adults. Over the age of 40 the additional radiation exposure, irradiation exposure, does not seem to increase risk of breast cancer so women over the age of 40 really should not be getting any increased risk of breast cancer at all from the mammograms but there are studies that are still looking into this further.