One thousand sets of female twins are helping researchers gain new insights into the causes of breast cancer.

Twin sisters Helen and Heather Worland have suffered from breast cancer and are now taking part in one of the largest breast cancer studies in Australia, providing researchers with invaluable information.

"Our mother also had cancer, so we were on high alert already and when Heather got cancer, obviously I was being vigilant" said 51-year-old Helen.

Professor John Hopper's research shows the twin who goes through puberty first often has a higher mammographic density, which increases the risk of developing breast cancer.

He know wants to examine how environmental factors affect genes and increase the risk of breast cancer, but he needs more twin volunteers.