Incorporating molecular profiling with mammograms at the time of diagnosis can help avoid overtreatment, a new study finds.

Researchers from the University of California in San Francisco, along with researchers at the Netherlands Cancer Institute said Monday that mammography appears to reveal slow to moderate- growth tumors in the current population, after comparing the biology of tumors detected more than 20 years ago to the tumors detected five years ago.

“A significant number of screen-detected tumors are very low risk,’’ said lead author Laura Esserman, director of the Carol Franc Buck Breast Care Center at the UCSF Helen Diller Family Comprehensive Cancer Center.

“It shows that we have an opportunity to improve care by using molecular predictors to recognize who has these ultra-low-risk or idle tumors, and safely minimize treatment,” Esserman said in a statement. She said the finding can help inform radiologists and surgeons about how often they should recommend biopsy for low-risk abnormalities seen on mammograms.

“If most of the cancer we find is low risk, then we may very well be able to test a less aggressive approach for the very low-suspicion findings on mammograms that turn out to be benign. Simple follow up may be the better approach,’’ Esserman added.

The researchers used MammaPrint, a diagnostic test that is FDA–approved, to investigate the biology of both sets of tumors, ones found 20 years ago before the advent of mammograms, and others found five years ago when routine mammograms were performed, so that the risk a tumor will metastasize to a different area in the body could be measured.

The results showed that the proportion of poor prognosis tumors varies significantly by age, and that the likelihood of having a good prognosis increases with age.

The researchers said the likelihood of a good or poor prognosis did not differ between the era before the widespread screening and the present time for routine screening for women who were younger than 40 years of age, and that young women were more likely to have poorer prognosis tumors than older women.

However, patients aged from 49 to 60 had significantly better prognoses for those who were diagnosed more recently. Researchers suggest that the recent demonstration using the 70-gene signature that is detected by the MammaPrint diagnostic test can be the reason for the difference between the results from two decades ago and the results from 5 years ago.

“The bottom line is that screen detection should be taken into account when patient treatment is planned,’’ Laura J. van ’t Veer, PhD, the senior author of the study and developer of the MammaPrint, said, according to a statement.

“We can use this information to guide treatment recommendations and as the basis for the development of clinical trials that test the safety of less aggressive treatments for patients with the lowest risk tumors,’’ van ’t Veer added.

The finding “provides information that will allow us to improve screening,’’ the authors said.

“Not only can this help us to guide the use of risk stratifying tools to avoid overtreatment, but it should also enable us to reset thresholds for biopsy for very low-risk mammographic lesions.”