Factors during adolescence may contribute to breast cancer risk later on...

Hot off the presses of the American Institute for Cancer Research (and excerpted from ScienceNow), it looks like researchers are uncovering some of the mysteries behind environmental influences on breast cancer risk in women. Read on for further details.

'Evidence pointing to adolescence as a vulnerable period for life-long breast health stems from both animal and human observational studies. During puberty, the structure of the breast changes as a network of branching ducts develops. Cells are dividing at a quicker pace and any carcinogen that cells are exposed to puts them at greater risk of essentially making a mistake copying the DNA from parent to daughter cell.

"Some of these changes occur and are latent for several decades, waiting for a second hit, for something else to go wrong that triggers breast cancer," says Lindsay Frazier, MD, a pediatric oncologist at Dana-Farber Cancer Institute who is currently conducting an AICR-supported study related to adolescents' diets and risk of breast cancer. "It’s possible [during this time] there are ways nutrition protects the cell from acquiring a genetic mistake, or likewise it could be more vulnerable to potential carcinogens in the diet."

Diet and Drinking
In studies on adolescent diet and later breast cancer, alcohol is one factor that has consistently linked to increased risk. Studies have produced conflicting findings for many other exposures, including vitamin D, milk, types of fat and vitamin E.

The challenge in replicating study findings may have a lot to do with human fallibility. The majority of studies investigating adolescent lifestyle habits ask women to recall their weight, physical activity and diet from decades earlier, a challenge to remember correctly. Unknowingly, recall bias may also play a factor. In several studies, when women diagnosed with breast cancer recalled their diet, the findings differed from women who were cancer-free. It’s possible that the cancer survivors were falsely recalling factors they thought might explain their disease.

In her research, Frazier is removing these possible measurement errors by using data from the Growing Up Today Study (GUTS), a group of approximately 9,000 girls who were ages 9-14 when the study began 13 years ago. (GUTS participants are the children of Nurses Health Study II participants.) The AICR-funded study is focusing on fiber and vitamin D; examining their link to types of benign breast disease (BBD) linked to increased risk of breast cancer.

Soy at Early Ages
Some of the earliest evidence suggesting a young girl’s diet may play a role in future breast cancer risk relates to soy. Researchers have long observed that Asian women, who eat soy as part of their standard diet, have a significantly lower breast cancer risk than Caucasian women. Yet when Asian women move to the West, their daughters’ risk becomes similar to that of Caucasian women.

After numerous laboratory studies and her recent review of the literature, Leena A. Hilakivi-Clarke, PhD, says the evidence shows that soy protects against breast cancer, but only when women were exposed to soy at young ages. A Professor of Oncology at Georgetown University Medical Center, Hilakivi-Clarke’s animal studies have found that soy’s genistein leads to several long-lasting changes, including activating a tumor suppressor gene and decreasing the estrogen receptor’s response to estrogen.

"There are so many different changes caused by soy and genistein; right now we don’t know which of these might be the critical ones. It’s likely multiple pathways."

The Puzzle of Body Fat Protection
Among adults, clear evidence shows that excess body fat increases the risk of post-menopausal breast cancer. Yet when it comes to body fatness of girls and adolescents, a growing body of evidence suggests the opposite.

In one of the larger studies, almost 200,000 participants who recalled their body fatness at young ages were tracked for 16 years. The study found that body fatness at young ages overall decreased later breast cancer risk; the greatest decrease in risk was observed for adolescent body fat. As body fatness increased, breast cancer risk declined. And the link was unaffected by adult weight.

Exactly how excess adolescent body fat may protect against breast cancer is not known. The next goal is to understand what is driving the association in order to focus on prevention, said Heather J. Baer, ScD, Instructor in Epidemiology at the Harvard School of Public Health and lead author of the study.

"This study is part of a bigger picture, looking at cancer risk over the life course…. Now we know there are a number of factors at different stages of life that could impact breast cancer risk many years later.'

Source - AICR Feb 23 newsletter. Original source excerpted from ScienceNow.