New York, Aug 13 (IANS): For women over the age of 80 with breast cancer, the chances of survival due to chemotherapy are significantly lower, says a study.

"Chemotherapy's reduced effect on the risk of mortality in older breast cancer patients could be due to several factors: tumours being less sensitive to chemotherapy, a decrease in dosage as the body gets weaker with age or chemotherapy killing healthy cells in addition to cancer cells," said lead author Xianglin Du, professor at The University of Texas Health Science Center at Houston, US.

For the study, the researchers examined data on 14,440 women diagnosed with breast cancer and 26,893 men and women diagnosed with colon cancer from 1992-2009.

All patients were over the age of 65.

Among the women who had breast cancer, chemotherapy treatment reduced the risk of death from all causes by 30 percent for women ages 65 to 69, 26 percent for women ages 70 to 74 and 24 percent for women ages 75 to 79.

For women over the age of 80, chemotherapy did not significantly reduce the risk of mortality.

However, when women over the age of 80 with breast cancer combined chemotherapy and an additional treatment with the drugs adriamycin and cyclophosphamide, they experienced a 29 percent reduced mortality risk, the study said.

While the benefit of chemotherapy in reducing the risk of mortality decreased with age for female breast cancer patients, men and women with colon cancer did not experience the same trend.

Chemotherapy remained effective for colon cancer patients until the age of 89.

The study was published in the Journal of American Geriatrics Society.