Diane Balma felt vindicated when she heard the news - Canadian researchers had discovered that women with dense breasts, making their mammograms difficult to read, had a far higher risk of cancer.

They found that women with the densest breasts had four to six times the risk of breast cancer compared with women with the fattiest, and easiest-to-image, breasts.

Writing in the New England Journal of Medicine, Dr. Norman Boyd of the Ontario Cancer Institute in Toronto and colleagues said breast density itself could be a risk factor for breast cancer.

The other risk factors include having a close relative with breast cancer, carrying one of the known BRCA breast cancer genes and never having borne a child.

Balma had none of the other risk factors, but was worried when she felt a lump in her breast 11 years ago at age 30.

“I wasn’t doing self-exams at the time,” said Balma, who is now director of public policy at the non-profit Susan G. Komen Breast Cancer Foundation. “I just happened to come upon it. It was quite large and pretty deep.”

She went immediately for a mammogram - not a routine recommendation for women under 40, but Balma was worried.

“It did not show on the mammogram,” said Balma in a telephone interview. She had dense breasts, which show up on an X-ray like a white mass of tissue. Tumors in fatty breasts usually show up more clearly.

Her radiologist, a doctor who specializes in reading X-rays such as mammograms and other scans, was not especially worried but ordered an ultrasound.

“I was relatively small-breasted. Even so, he was barely able to find it on the ultrasound,” Balma said. “When he did see it, his words to me were, ‘You know, you are too young. I wouldn’t worry about this. I am sure it is not cancer.’”

But it was.

LIFE-SAVING DECISION

“I decided to have it removed and it was a decision that saved my life,” Balma said. Her surgeon discovered a very large tumor that turned out to be an aggressive type of cancer.

Balma eventually had both breasts removed and endured six rounds of chemotherapy. She has been cancer-free for 11 years.

“I have always known that dense breast tissue makes breast cancer harder to detect. But I also wondered if it brought a greater risk of breast cancer,” Balma said.

The Canadian study, published on Thursday, appeared to confirm that.

Breast cancer will be found in 180,510 men and women in 2007 in the United States alone and will kill 40,900, according to the American Cancer Society. Globally, it affects 1.2 million people a year.

The deaths are almost exclusively in people whose cancer is found too late, and young women under 40 make up about 5 percent of that number. Most cases are in women past menopause.

Mammograms are only recommended for women who know they are at high risk, and for women over the age of 40. How would a younger women such as Balma even know she had dense breasts and thus perhaps have a higher risk?

“That is a question that has not been answered yet,” said Dr. Cheryl Perkins, senior clinical adviser at the Foundation.

“We need more study of breast cancer in young women. We comprise far fewer breast cancers but our tumors tend to be more aggressive and more deadly,” said Balma.

Perkins agreed. Younger women have fewer treatment options, she said. “Those types of breast cancer tend to metastasize (spread) early. They tend to metastasize to the brain,” Perkins said.