Metal Cadmium: Ups Breast Cancer Risk?
Sources of the Metal Include Tobacco Smoke and Some Foods
June 20, 2006 -- A heavy metal called cadmium is drawing scientists' attention for its possible connection to breast cancerbreast cancer.
A brief report in the Journal of the National Cancer Institute links high cadmium levels to increased breast cancer risk.
But it's not yet clear if high cadmium levels actually cause breast cancer, write the researchers.
Jane McElroy, PhD, of the University of Wisconsin Comprehensive Cancer Center in Madison, and her team say their findings are "provocative." They call for further studies to see if high cadmium levels raise the risk of breast cancer or simply signal some unknown aspect of the disease or its treatment.
Cadmium is a toxic heavy metal that can build up in the body over time. It has been labeled a "probable human carcinogen" by the U.S. Environmental Protection Agency.
"Probable" human carcinogens have been shown to cause cancer in animals but only limited human data from observational studies exist for them, McElroy's team explains.
People may be exposed to cadmium if they work with cadmium or in refining and smelting. The U.S. government limits such on-the-job exposure.
Tobacco smoke is another source of cadmium exposure. And some foods -- such as liver, kidney, crustaceans (lobsters, crabs, and shrimp), and canned fish -- "may potentially be high in cadmium," write McElroy and colleagues.
Breast Cancer Study
McElroy's study included 246 women aged 20 to 69, who had been diagnosed with breastcancercancer up to two years before the study and were recorded in Wisconsin's cancer database.
For comparison, the researchers also studied 254 women without breast cancer randomly chosen from Wisconsin driver's license lists.
Because breast cancer becomes more prevalent as women grow older, the groups were matched for age.
All of the women provided urine samples and took a 35-minute telephone interview about their physical activity, reproductive history, alcohol consumption, height and weight, use of oral contraceptives and hormone replacement therapy, personal and family medical history, smoking status, and dietary factors.
When McElroy's team measured cadmium levels from the women's urine samples they found that women with the highest cadmium levels had twice the breast cancer risk of those with the lowest levels.
The results held after the researchers adjusted for other established breast cancer risk factors, as well as for smoking, which hasn't been firmly linked to breast cancer. However, the study included few current smokers (33 breast cancer patients and 31 women without breast cancer), making it tough to tell how smoking affected cadmium levels.
McElroy and colleagues also screened for consumption of some foods that can be high in cadmium and found no links between those foods, cadmium levels, and breast cancer risk.
The study doesn't prove cadmium exposure causes breast cancer. It will take more research to figure that out, McElroy's team notes.