Adding to the already heated debate about mammograms comes a new study suggesting that women in their 40s may benefit greatly from them. The British study echoes a recent Swedish study finding that women in their 40s significantly reduced their risk of breast cancer mortality when they underwent screening.

The mammogram question is so controversial these days because the United States Preventative Services Task Force (USPSTF) now recommends that women not be screened till they are over the age of 50. On the other side of the ring is the American Cancer Society (ACS), which says that women should begin screening at age 40 for full benefit.

Though the study offers some good evidence for earlier mammograms, one drawback is that the survival rates for the women in the study were only predicted — in other words, the researchers did not measure how likely the women were to survive after their cancer was treated.

The current study followed over 6,700 women under 50 who were at "intermediate" risk for breast cancer, meaning that they had multiple family members with breast cancer or one relative who developed breast cancer younger than age 40 (about half the women in the study fell into the latter category). Not many women in the study were likely to have the BRCA mutation (which puts women at high risk) because the researchers wanted to study women of intermediate risk. Most of the women in the study were in their early 40s (40-44) when the study began. Women had mammograms once a year for about 4 years.

Mammogram screening detected breast cancer in 77% of the total cases of breast cancer (another 21% of breast cancers were diagnosed after symptoms developed). This corresponded to a 79% sensitivity rate for the mammograms; for invasive cancers, the sensitivity was 72%. The survival rate after 10 years for women who underwent screening was predicted to be 81% for women who underwent screening, vs. 72% for those who did not. Women who were screened also had smaller tumors at the time of detection, and their breast cancers were less likely to be "node-positive" (which indicates that cancer has spread to the lymph nodes).

Though the study offers some good evidence for earlier mammograms, one drawback is that the survival rates for the women in the study were only predicted — in other words, the researchers did not measure how likely the women were to survive after their cancer was treated. Survival rates were calculated based on the size and severity of the breast cancers detected. While more research will be needed to determine just how mammograms affect survival rates of the patients, the study adds some nice evidence to the pot, showing that mammograms under 50 may offer some big benefits in early detection. As always, it is important to speak with your doctor to determine whether early screening is right for you.

The study was carried out by researchers at The London School of Medicine and Dentistry at Queen Mary University of London, and published in the November 17, 2010 online issue of The Lancet Oncology.