Poor breast cancer patients skipping hormone pills

* Study looked at women on Medicaid in North Carolina

* May explain higher rates of breast cancer deaths

CHICAGO, May 18 (Reuters) - Despite having insurance, many poor women with breast cancer do not take hormone pills needed to keep their cancer in check, raising their risks that the cancer will return, U.S. researchers said on Monday.

The study of women in North Carolina covered under the Medicaid insurance program for the poor found many were not taking hormone therapy.

"Even though these women had continuous health insurance with low prescription co-pays, we found that only 64 percent of them were filling any prescriptions for hormonal therapy within 12 months after being diagnosed," Dr. Gretchen Kimmick of Duke University Medical Center, whose study appears in the Journal of Clinical Oncology, said in a statement.

Taking hormone-blocking drugs can help women survive breast cancer and can prevent it from returning if they have hormone-receptor positive breast cancers, in which a hormone is driving the cancer.

Women in the study had their tumors removed surgically and most -- 88 percent -- were prescribed tamoxifen to keep the cancer from coming back. Other hormone treatments included AstraZeneca's (AZN.L) Arimidex or anastrozole, Novartis's (NOVN.VX) Femara or letrozole, or Pfizer Inc's (PFE.N) Aromasin or exemestane.

"Our study shows that in the year following the initial prescription fill, 40 percent of the women were not regularly taking their hormonal therapy," Kimmick said in a statement.

Of those who had started taking the drugs, 20 percent quit before the end of the first year, they said.

"This is alarming since women are even more likely to discontinue use over subsequent years," Kimmick said.

The study did not show why these women failed to take their pills. In other studies, women have listed side-effects, cost and a lack of understanding about why the drugs are needed.

Curiously, the team found that single women in the study were more likely to take their medications than married women.

"We lack a good explanation for this finding, but suspect that it reflects a different pattern of social support in this particular population," the team wrote.

Kimmick said researchers need to find new and effective ways to get low-income women to take their medications.

"If we can improve use of these very effective treatments, we may decrease the breast cancer mortality rate among this population," she said.

Breast cancer is the top cause of cancer death among women worldwide, with an estimated 465,000 deaths annually, according to the American Cancer Society.

(Editing by Maggie Fox)