Social stress has been shown to increase the risk of uterine cancer in a species of postmenopausal monkeys that have similar reproductive physiologies as women. The study also suggests that moderate alcohol consumption does not increase breast cancer risk."To our knowledge, this is the first report of an association between social subordination stress and markers of increased cancer risk in an animal model," wrote researchers from Wake Forest University Baptist Medical Center.
Their study is published in the current issue of Menopause, the journal of the North American Menopause Society.
The study involved 48 cynomolgus macaques. These monkeys have a 28-day menstrual cycle, their mammary tissues are similar to women, and their organ responses to circulating hormones — like estrogen — are similar to women. The monkeys were fed a diet mimicking the average North American diet in fat and cholesterol. Half of the animals were trained to drink the equivalent of 2 alcoholic drinks a day through a syringe. Then all of the monkeys were monitored for 26 months, with social status being determined monthly.
The monkeys were placed in groups so they would naturally establish a hierarchy. The researchers observed the outcomes of aggressive interactions between cage mates. The animal to which all the others in the group submitted was designated the first rank monkey. The second rank monkey was the animal that all but the first rank monkey submitted to, and so forth. The subordinate monkeys received more aggression, were more vigilant, were groomed less, and spent more time alone than the dominant animals.
Previous research has shown that subordinate monkeys have increased heart rates, more of the stress hormone cortisol, and more cardiovascular disease. In this study, the subordinate monkeys were at an increased risk for endometrial cancer as a result of cellular changes in the uterus. Uterine cancer affects 1 to 2 percent of women and is the most common cancer in older women.
The researchers observed that the subordinate monkeys also had changes in their breast tissue, but the changes were not as concerning as the uterine changes. For both the breast and uterine studies, the researchers evaluated the type and quantity of cells, the density of tissue, number of dividing cells, and the number of progesterone and estrogen receptors in the breasts and uterus. They also measured the levels of sex steroids, such as estrogen and cortisol, which may be markers for cancer risk.
Several studies over the last decade have shown an association between alcohol consumption and breast cancer risk, but it is not clear why the risk is elevated. Some experts believe that alcohol elevates the levels of circulating estrogens — these hormones have been shown to increase the risk of breast and endometrial cancers. But in this study the researchers saw no effects of chronic moderate alcohol consumption on cell growth, nor did alcohol alter the level of circulating sex hormone concentrations in the monkeys.
The researchers say their results are precautionary — that postmenopausal women who are placed under social stress, which might be caused by isolation, hostile experiences, or lack of control over a situation, may place women at increased risk for endometrial cancer. It might be important for researchers to study the impacts of stress and socioeconomic status on breast and endometrial cancer risk in women.
