updated 6/5/2007 8:42:31 PM ET 2007-06-06T00:42:31

A Harvard study released Monday supports earlier findings by a panel of experts that having an abortion doesn’t increase a woman’s risk of getting breast cancer.

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However, this latest analysis isn’t likely to convince all those opposed to abortion. Three states — Texas, Minnesota and Mississippi — require doctors to warn women seeking abortions of the purported link to breast cancer “when medically accurate,” letting doctors make that determination based on current scientific evidence.

In 2003, a group of scientists convened by the National Cancer Institute concluded abortion did not raise the risk of breast cancer.

What evidence shows is that childbearing before the age of 35 reduces a woman’s breast cancer risk and breast-feeding also helps, said the new study’s lead author, Karin Michels of Harvard Medical School. Scientists believe breast cells that have gone through a full-term pregnancy gain protection against cancer, she said.

Studies that found a link between abortion and breast cancer have relied on reports from women with cancer and healthy women about whether they’d had abortions in the past. The women with cancer may have been more likely than healthy women to report abortions as they searched for reasons why they got sick, Michels said.

The new study, appearing in Monday’s Archives of Internal Medicine, looked at data from 105,716 women participating in the Nurses’ Health Study, which was established in 1976 to study a wide range of health issues affecting women.

The women, ages 29 to 46 at the start of the study, were followed for 10 years. Every two years, they were asked about abortions, miscarriages and new breast cancer diagnoses. The researchers looked at medical records to confirm the diagnoses.

The researchers found no greater rate of breast cancer among the women who reported having abortions, compared to the other women. They saw no greater risk associated with multiple abortions and no greater risk linked with miscarriages.

Joel Brind, a biochemist with City University of New York’s Baruch College, was the sole dissenter to the 2003 NCI report on abortion and breast cancer. He said the new study is flawed because it included very recent abortions — too recent for them to contribute to the development of cancer. Including those abortions in the analysis may have diluted the cancer rates, he said.

Michels said more than 90 percent of the abortions in the study occurred before 1993.

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