P&S Journal: Spring 1994, Vol.14, No.2
Smoking, Radiation Therapy: Dangerous Mix for Breast Cancer
In a preliminary finding that may have treatment implications for breast cancer patients who smoke, P&S researchers have found a relationship between the use of radiation therapy for breast cancer and an increased risk of lung cancer in non-smokers and a dramatically increased risk for smokers. The findings were published in a March issue of Cancer.
The study, conducted by Dr. Alfred I. Neugut, associate professor of clinical medicine and of public health, used data from the Connecticut Tumor Registry on women who received radiation therapy before 1980 when doses of radiation were higher than they are today. Dr. Neugut and his colleagues found the use of radiation therapy for women with breast cancer raised their risk of lung cancer almost three times compared with breast cancer patients who did not receive radiation therapy.
Breast cancer patients who smoked and received radiation therapy had more than 30 times the risk of lung cancer compared with non-smokers who did not receive radiation. These risks were observed 10 years after the breast cancer diagnosis, which is consistent with what is known about radiation-induced cancers. No radiation effects were observed in the lung until 10 years after the radiation treatment.
The study compared 89 breast cancer patients diagnosed with lung cancer since 1986 with more than 1,000 breast cancer patients diagnosed during the same period with malignancies not related to smoking or radiation. "This is the first time that a combined risk for lung cancer from cigarette smoking and therapeutic radiation has been shown. Women who have been exposed to both cigarette smoke and radiation therapy may have a large potential risk for developing lung cancer," says Dr. Neugut. "That the excess lung cancer was on the same side as the breast that was irradiated (ipsilateral) and not the contralateral lung (the lung not directly irradiated) strongly indicates a causal relationship and not a statistical fluke."
Current risks associated with radiation therapy may be considerably lower because improved technology delivers a narrower, more focused radiation beam and because of widespread use of radiation following lumpectomy, in which the radiation is directed toward the breast tissue, away from the chest wall and lung.
The findings may be important for smokers who have breast cancer as they consider radiation in their treatment. "Women with primary breast cancer have a choice of mastectomy vs. lumpectomy with radiation therapy. This information needs to be considered by women who smoke when making those choices," says Dr. Neugut. "Although there were no data on the effect of stopping smoking prior to treatment, this would certainly be a reasonable recommendation under any circumstances."
This research confirms a previous study by Dr. Neugut's group that showed a doubling of lung cancer risk following breast cancer radiation therapy and extends the findings to emphasize the higher risk of lung cancer for smokers, an effect also observed in uranium miners who smoked.
The Connecticut Tumor Registry has information on more than 40,000 women treated for breast cancer during the past 45 years but has compiled smoking information only since 1986.
"Our findings must be considered preliminary because there were some gaps in the data and the numbers were small," says Dr. Neugut. "However, the magnitude of the risk and the consistency of the findings both within the study and with our prior knowledge of the effect of radiation on the lung support the validity of the findings."
Dr. Neugut is planning a larger study to confirm and better define these findings. His group also is exploring the combined effects of radiation therapy and smoking on patients with Hodgkin's disease and lung cancer for similar effects.