Glitch in Vitamin A Metabolism May Be Linked to Breast Cancer
March 14, 2000 (Atlanta) -- Nearly a fourth of all breast cancer tumors lack a protein that is involved in vitamin A metabolism, a new study has found. Women with a deficiency of this protein, called CRBP (cellular retinol binding protein), may be at increased risk for cancer because their cells are unable to use protective vitamin A from their diets, researcher Rafael Mira-y-Lopez, MD, PhD, tells WebMD.
The study, which appears in the March 15 issue of the Journal of the National Cancer Institute, found that CRBP was lacking in about 24% of human breast cancers, says Mira-y-Lopez, an associate professor of medicine in the Division of Medical Oncology, department of medicine, at Mount Sinai School of Medicine in New York. Earlier research, he tells WebMD, "implicated CRBP in vitamin A uptake and metabolism." If this is true, breast cancers without this protein would not be able to use vitamin A, he says. Vitamin A is directly involved in cellular formation -- the process that goes awry in cancer. It has also been shown to have strong anticancer effects in both animals and humans.
The researchers compared samples of normal breast tissue obtained from women having breast-reduction surgery to tissue samples from women with breast cancer (some of which included healthy surrounding tissue). They found CRBP in all 15 of the samples from breast-reduction patients. In addition, 33 of 35 of the samples of normal breast tissue surrounding the breast cancers had CRBP. But the protein was not seen in 12 of the 49 actual tumors.
The findings suggest that even for some women who have normal dietary intake of vitamin A, their bodies' use of these vitamins may be compromised by the absence of CRBP, Mira-y-Lopez says. For these women, eating extra carrots or taking supplements may be useless.
In truth, says Mira-y-Lopez, the exact function of this protein is not clear, and the study's findings may mean nothing. For now, though, all that's really known is that this protein is not found in some breast cancers, and the simplest interpretation is that "cancer cells turn it off."
"It's very hard to say what the findings mean because we don't have follow-up data," says Mira-y-Lopez. Any clinical application of these findings is quite a ways off, but if the researcher's hunches are correct, CRBP could be a marker for a predisposition to breast cancer that patients could be tested for. More important, the problem should not be especially difficult to correct. "If lack of this protein is really preventing cells from utilizing vitamin A, ... then this is easy to bypass by giving [patients] retinoic acid," Mira-y-Lopez says. Retinoic acid is the active form of vitamin A in the body.
"This is a pilot study," Mira-y-Lopez says, "so the first thing to be done is to validate it in a large number of cases." He says the findings are important because they point researchers in an entirely new direction. They introduce an additional variable -- how well cells use vitamin A. If it turns out that CRBP really does change the efficiency with which cells use vitamin A -- and that's a big if -- then the protein could become a key player. For now, he says, "the bottom line is that it's an interesting observation."