Vitamin D: New Weapon in Battle Against Breast Cancer?

It boosts benefits of radiation therapy, study says

WEDNESDAY, April 23, 2003 (HealthDayNews) -- The addition of a vitamin D analog to radiation therapy is more effective in killing breast cancer cells than radiation alone, a new study suggests.

About 200,000 American women are diagnosed with breast cancer each year and about 40,000 die. Radiation therapy is often used before surgery to reduce the size of tumors and after surgery to reduce recurrence of tumors.

Other studies have shown vitamin D interferes with tumor growth in both cell cultures and animals, study co-author David A. Gewirtz says. This has been shown for both breast and prostate cancer, he notes.

Because high doses of vitamin D can be toxic, Gewirtz and his colleagues are experimenting with vitamin D analogs, modified forms of natural vitamin D that are less toxic. Their goal is to see if these analogs can enhance the response to radiation therapy.

In this study, Gewirtz, a professor of pharmacology and toxicology at Virginia Commonwealth University, and his colleagues found that when they treated breast cancer cells in a laboratory setting with normal doses of a vitamin D analog (ILX 23-7553) before radiation, the response to radiation was enhanced.

Lower doses of radiation were needed and there was an increase in tumor cell death, Gewirtz says. In fact, vitamin D helped reduce the number of cancer cells by almost 30 percent more than radiation alone.

The study appears in the May issue of Cancer Chemotherapy and Pharmacology.

After treatment with the vitamin D analog and radiation, tumor cells continued to die for seven days, while cells treated with radiation alone did not. Treatment with the vitamin D analog was three times more effective in preventing new tumor growth, compared with radiation therapy alone, the study says.

"In addition, this combination was not toxic to normal cells," Gewirtz says.

He cautions these results were produced in cell cultures, and one should be careful before applying them to treating breast cancer in women. Currently, the vitamin D analog is not being tested in humans in the United States. However, it is being tested in humans in Europe, he says.

In a forthcoming paper, Gewirtz says he and his colleagues show the same effect is found when breast tumors are grown in mice.

"There is also evidence that using a vitamin D analog and radiation prevents cancer cells from growing back," Gewirtz says. Based on these findings, combined treatment with a vitamin D analog and radiation may contribute to preventing recurrence of cancer, he adds.

"We think that this treatment may also have implications for treating radiation-resistant brain tumors and prostate cancer," Gewirtz says. "That's the direction of our work."

Dr. Lamar McGinnis, a medical consultant for the American Cancer Society, says that although the effect was only seen in cultured cells, "it appears that this vitamin D compound is a radio sensitizer for cancer cells and results in a greater kill rate with a sustained effect."

With radiation therapy, there is always a balance in killing cancer cells and protecting normal cells, he adds. If these findings pan out in human trials, controlling cell growth within tumors could be enhanced, he notes.

"It is an interesting observation and I await the results of clinical trials, particularly since this compound seems to have no significant side effects," McGinnis says. "If it works out, it could offer a significant benefit to cancer patients."

More information

To learn more about breast cancer, visit the National Breast Cancer Coalition. For more on vitamin D, check with the National Institutes of Health.

SOURCES: David A. Gewirtz, Ph.D., professor, pharmacology and toxicology, Virginia Commonwealth University, Richmond; Lamar McGinnis, M.D., medical consultant, American Cancer Society, Atlanta; May 2003, Cancer Chemotherapy and Pharmacology
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