Women have long been told that the best defense against breast cancer is a mammogram, but now it appears a new study is questioning the worth of the screening process.

According to a report in the HealthDay News, a Canadian study has found the annual screenings have shown no evidence that they're reduced the death rate among women ages 40 to 59.

The study followed 90,000 women for 25 years, and found while more breast cancers were detected with the help of mammorgrams, they did little if anything to prevent women from dying of the disease.

It also found slightly more than 20% of the test group actually were adversely affected by the annual testing by over-diagnosis and unneccessary rounds of therapy.
The research also suggests improved technology and therapy are saying more lives than 40 years ago.