The US Preventive Services Task Force (USPSTF), an independent panel of experts that receives federal funding, previously said that women in their 40s should make an individual decision about when to start mammograms based on their health history and reserved its mandatory recommendation for people turning 50.
Its new guidance was based on a review of evidence and a modeling study published in the Journal of the American Medical Association (JAMA), and updates final guidelines last issued in 2016.
"More women in their 40s have been getting breast cancer, with rates increasing about two percent each year, so this recommendation will make a big difference for people across the country," Task Force chair Wanda Nicholson said in a statement.
"By starting to screen all women at age 40, we can save nearly 20 percent more lives from breast cancer overall."
Breast cancer is the second most common cancer overall and the second most common cause of cancer death for women in the United States, with more than 43,000 deaths last year.
Black women are 40 percent more likely to die of the disease than white women, and so ensuring they start screening at 40 "has even greater potential benefit for Black women," said Nicholson.
- Welcomed by doctors -
The US guidance goes beyond that of other wealthy countries with advanced health care systems, including Britain, France and Germany, which recommend routine screening begin at 50.
Medical oncologist Nancy Chan, director of breast cancer clinical research at NYU Langone's Perlmutter Cancer Center, told AFP that in practice, US health care providers were already shifting to screening women starting at 40.
"That's been the trend so far, but it is always important to actually have the guidelines appropriately reflect what we've been clinically practicing as well," said Chan, adding the recommendation may increase the likelihood of insurance carriers paying for screening if they did not previously.
"Diagnosing breast cancer early stage means better prognosis, higher cure rate -- we're talking more breast cancer survival."
Beyond the generalized recommendation, Chan also urged women in their 40s to also consult with their doctors who could provide them tools to assess their personal lifetime risk of getting breast cancer, based on family history and other factors, and whether they can make lifestyle changes to lower it.
- More research needed -
The new recommendation applies to nearly all women -- those who are at average risk of breast cancer, as well as those with a family history of breast cancer, and those with dense breasts.
Nearly half of all women have what's known as dense breast tissue, which they generally only find out during their first mammogram. Dense breast tissue increases their risk for breast cancer and means that mammograms may not work as well for them.
"Unfortunately, there is not yet enough evidence for the Task Force to recommend for or against additional screening with breast ultrasound or MRI," the panel said, urgently calling for more research.
The guidance also doesn't apply to those with a personal history of the disease, or those at very high rise due to certain genetic markers, or who have a lesion detected on previous biopsies. These individuals could benefit from more regular screening, in consultation with their doctor.
While the recommendation is for those from the ages of 40 to 74, the experts said they were uncertain about how the benefit-to-risk may shift after the age of 75, and more research was needed here too.
While screening is a powerful tool in the fight against cancer, there are also limits, the task force said, explaining why it is not recommending annual mammograms, which some experts have called for.
Over-testing increases the potential for harms, such as false positives, or receiving treatment that wasn't required, the USPSTF said.
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