Breast cancer is often considered more deadly among younger women, but older women - particularly those over 75 - are actually more likely to die of the disease, according to an international study.
Researchers, who tracked thousands of women and published their findings in the Journal of the American Medical Association, said that among women diagnosed with a certain common type of breast cancer, those over 75 years-old were 63 per cent more likely to die of it than women under 65.
"I suspect it's undertreatment. We did show the rates of chemotherapy and radiation therapy are less in the older group,"said Stephen Jones, medical director at US Oncology Research in Texas and one of the study's authors.
The study focused on nearly 10,000 women who had already gone through menopause and who had been diagnosed with hormone receptor-positive breast cancer.
That's the most common type of the disease and is considered less dangerous than the hormone receptive-negative types because it is often slower growing and might respond to hormone treatments.
Younger women are more likely than older women to have the receptor-negative cancer, and they also tend to be diagnosed at a later stage, leading to the idea that breast cancer is more deadly for them.
In the study, researchers found that five out of every 100 women diagnosed under age 65 and six out of every 100 women diagnosed between 65 and 74 years-old died from breast cancer within five years.
But among women over age 75 at the time of their diagnosis, eight out of every 100 died from the cancer.
"What's different in older women is they tend to get lesser and poorer treatment," said Hyman Muss of the University of North Carolina School of Medicine, who was not involved with the study.
Nearly all the women in the study went through surgery, but just half of the women over age 75 had radiation, and just five per cent had chemotherapy.
In comparison, 75 per cent of women under age 65 received radiation and 51 per cent had chemotherapy.
"There are beliefs that older women do not benefit from chemotherapy as much as younger women, and that the side effects are worse," said Gerrit-Jan Liefers, a researcher at Leiden University Medical Centre in The Netherlands who also worked on the study.
He added that patients themselves may also be more hesitant to treat their cancer aggressively.
Though a recent study found that the rates of breast cancer deaths have been slowing, older women have had smaller gains than younger women, which the authors attributed in part to less aggressive treatment, perhaps due to concerns the treatment could cause more problems than the disease.
Muss said it's possible to overtreat elderly patients, but that otherwise healthy women in their 70s would likely benefit from chemotherapy.
"We need to teach doctors not to think of a person's chronologic age, but think of their functional age," he said.