Among the causes of death that threaten individuals 35 and older, heart disease ranks number one, killing about 900,000 American every year. Cancer, responsible for claiming the lives of 550,000 yearly in the U.S., comes in second place. But heart disease and cancer share yet another bond: Ironically, the quest to cure cancer has sometimes given the incidence of heart disease a boost. Here, three studies that document how certain cancer treatments have unwittingly led to incremental increases in heart disease.

Breast Cancer Radiation Therapy: An article published in the March 7, 2007 issue of the Journal of the National Cancer Institute claimed that women who received radiation therapy for breast cancer in the 1970s and '80s run an increased risk of heart disease. Researchers from the Netherlands Cancer Institute in Amsterdam examined the records of some 4,000 women who had been treated between 1970 and 1986. Those who underwent radiation therapy from 1970 to 1979 were 1.5 times more likely to suffer heart disease than those who did not receive radiation, while women who were treated between 1980 and 1986 faced a heart disease risk that was 1.35 times greater. Studies on the causal link between heart disease and more modern radiation therapies have so far been inconclusive.

Hedgehog Antagonists: So named because flies that carry an abnormal version of the gene that this anticancer drug is based on resemble the spiny mammals of video game fame, hedgehog antagonists have been shown to inhibit cell growth and are being tested against cancers such as basal cell carcinoma and pancreatic cancer. But researchers at Washington University School of Medicine in St. Louis have revealed that signaling pathway used by hedgehog genes also plays an important role in the maintenance of the heart's blood vessels; therefore using drugs to suppress it may deprive the heart muscle of oxygen. Their study found that if the signaling pathway in a mouse were completely blocked, then many of its small coronary blood vessels would disappear. Although this means that cancer patients who are involved in this therapy should monitor their cardiovascular health closely, it could also represent a milestone in the treatment of heart disease through the use of drugs that augment the hedgehog signaling pathway in order to promote healthy blood vessels.

Prostate Cancer Therapy: Men who undergo androgen deprivation therapy (ADT) for prostate cancer need to keep an eye on how the treatment affects their cardiovascular health, according to researchers at the University of Texas Health Science Center. They reviewed 14 studies of the side effects related to ADT and found that men receiving that therapy faced a 17 percent greater risk of heart-disease-related death.

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Kory J. Lavine, Attila Kovacs, and David M. Ornitz, Hedgehog signaling is critical for maintenance of the adult coronary vasculature in mice, J. Clin. Invest.  118:7 doi:10.1172/JCI34561;

Lockwood G. Taylor, Steven E. Canfield, and Xianglin L. Du. Review of Major Adverse Effects of Androgen-deprivation Therapy in Men With Prostate Cancer. Cancer, Online April 27, 2009; Print Issue Date: June 1, 2009 DOI: 10.1002/cncr.24283;