A study looking at women with breast cancer found a small group to be at high risk of developing ovarian cancer, according to a report Aug. 28 in The Lancet (online edition).

Researchers said that young women diagnosed with breast cancer who have a family history of either breast or ovarian cancer are at a greater risk of developing ovarian cancer, compared to women without a family history of either disease.

The study looked at the role of family history of breast or ovarian cancer to predict a woman's risk of getting ovarian cancer after she was diagnosed with breast cancer. They relied on the detailed family, health, and death histories compiled by the Swedish government.

The study was conducted by Kyell Bergfeldt, MD, and colleagues from the Karolinska Institutet in Stockholm, Sweden; Umea University Hospital in Umea, Sweden; and Kuwait University, Kuwait.

Age at onset of breast cancer, and the number and age of relatives with a history of breast or ovarian cancer, were used to gauge the women's risk of ovarian cancer after a breast cancer diagnosis.

By linking information in the Swedish data registries, the researchers were able to study the records of more than 30,500 women with breast cancer who were diagnosed with breast cancer between 1958 and 1998.

They were also able to link these women with more than 146,000 first-degree relatives (mothers, fathers, sisters, brothers, daughters and sons) and look at their family history of breast or ovarian cancer.

After following the women for an average of six years, the researchers found that if a woman was under the age of 40 at the time her breast cancer was diagnosed, her risk of getting ovarian cancer was tripled.

But the most striking findings were in all of the women with family histories of breast and ovarian cancer in a first-degree relative. Their risk of ovarian cancer was increased a little over four times.

A woman with the same family history diagnosed before age 40 had a more than seven-fold increased risk of ovarian cancer.

Looking at the results a different way, the authors reported that if a woman had breast cancer diagnosed before age 40, and there was a family history of ovarian cancer, her risk of getting ovarian cancer was 17 times that of a woman without breast cancer.

If a woman with breast cancer had no family member (other than herself) with a history of breast or ovarian cancer, her personal risk of developing ovarian cancer was increased 60%, the authors said.

Finally, if a woman had breast cancer, and had a relative who had ovarian cancer, the woman had a 10% chance of developing ovarian cancer over the 30 years following the breast cancer diagnosis.

By comparison, northern European and American women with no family history have a 1% risk of developing ovarian cancer before age 70, according to a Lancet press statement.

"Our most interesting finding, however, was the striking excess risk…in women with early-onset breast cancer, and a family history of breast cancer, or especially ovarian cancer," wrote the authors. "Also noteworthy is the finding that patients with a family history, especially if an ovarian cancer is present, have a high risk of ovarian cancer."

One of the questions raised by the study is how to explain the link between breast and ovarian cancer.

Overall, about 5% of women have BRCA mutations, according to the report. But, hereditary factors may account for up to 25% of breast and ovarian cancer cases that occur in families, they said.

"Our study lends support to the theories of a connection between as yet unknown genes and cancer susceptibility," wrote the authors.

If their results are confirmed in other studies, the small group of women with breast cancer at high risk of ovarian cancer may be identified, said the authors.

In this group of women, "counseling, and perhaps even prophylactic (meaning a preventive measure, as the ovaries are cancer-free) oophorectomy, might be considered," they wrote.

Harold Burstein, MD, an assistant professor at Harvard Medical School and on the staff of the breast oncology center at the Dana Farber Cancer Institute in Boston, said the results of the study were predictable.

"We know there are relations between breast and ovarian cancer. We also know that the BRCA genes account for this relationship," said Burstein.

But Burstein also underlined the other side of the news. "Women who don't have a family history of breast or ovarian cancer and are older than 49 when they are diagnosed with breast cancer have a very low risk of getting ovarian cancer," he said.

"Most genetic epidemiologists (cancer researchers who study genes) feel the increased risk is in women with BRCA mutations," he said. However, he also noted that to look for mutated BRCA genes in this study would not be practical.

In the US, most experts consider the number of breast and ovarian cancers caused by BRCA gene abnormalities to be around 5% to 8%, said Burstein. And, experts also consider a similar number of breast and ovarian cancers to be related to some other unknown or uncertain genetic change, particularly for women younger than 40 who develop cancer.

Regarding advice for women, Burstein noted, "These studies identify women at greater risk of ovarian cancer down the road." He emphasized that there is no simple guideline for a woman to follow for monitoring or whether she should have a preventive oophorectomy.

"These women might want to talk to their doctors about future tests and possible options. In the end, it's about communication with your physician," concluded Burstein.