AMNA NAWAZ: A key scientific panel has updated its recommendations on breast cancer screenings.

Ali Rogin has more on the changes that could potentially save thousands of lives -- Ali.

ALI ROGIN: Amna, the U.S. Preventive Services Task Force is now recommending that all women start getting biennial mammograms at age 40 until they turn 75.

The new guidelines replace ones from 2016, which recommended biennial screenings starting at age 50 and that starting them any earlier should be a matter of individual choice.

But these new guidelines are still out of step with some major medical associations and cancer advocacy groups.

Dr. Wanda Nicholson is the chair of the U.S. Preventive Services Task Force and joins me now.

Dr. Nicholson, thank you so much.

Why did the USPSTF make these recommendations?

And how many lives is it going to save?

DR. WANDA NICHOLSON, Chair, U.S. Preventive Services Task Force: Well, we know that breast cancer is the second most common cancer in women and the second most common cause of cancer deaths in women.

The latest science clearly shows that by starting at age 40 and screening every other year until age 74 can save even more lives from breast cancer and, in fact, can save up to nearly 20 percent more lives.

And this corresponds to about 25,000 more women whose lives are saved.

We think that's a huge win for women.

ALI ROGIN: As we did mention, these guidelines are out of step with some advocacy groups and medical organizations.

I spoke earlier today with a board-certified radiologist, Dr. Robyn Roth.

She raised some concerns.

I want to play for you some of her comments and then ask you about them.

DR. ROBYN GARTNER ROTH, Cooper University Health Care: I think that they missed the mark in a number of ways, the largest way being the every-two-year screening interval, which experts like myself will tell you that annual screening mammography saves the most lives.

These guidelines do not endorse supplemental screening in women with dense breast tissue.

And I think that is a major downfall of these recommendations.

ALI ROGIN: I want to ask first about the two-year interval.

You actually said in a recent interview that annual screening might find some cancers earlier.

So, why not recommend annual breast screening?

DR. WANDA NICHOLSON: Well, the task force's role is to look for the strongest evidence possible to help guide women as to how they should be screened and how often to be screened.

And we recently looked at the evidence and looked across all the evidence, comparing the benefits and harms of different screening strategies.

We found a much more favorable balance of benefits and harms for individuals undergoing screening every other year compared to annually.

ALI ROGIN: And what are some of those harms?

DR. WANDA NICHOLSON: Well, there can be various harms.

First, the first leading harm can be a harm of potentially false positives.

And what we found is that, if you compare annual screening to every-other-year screening, women who undergo annual screening can have up to 50 percent more likely to have a false positive result.

So what does that mean?

It means that then the next step may be a breast biopsy that could otherwise be normal, and, that way, they underwent sort of an unnecessary biopsy.

It can also lead to issues of overdiagnosis and overtreatment and a possibly exposure to treatments that may have some harmful side effects.

So, again, when we compared the balance of benefits and harms, it was a more favorable balance for every-other-year screening.

ALI ROGIN: And when weighing the potential for false positives against the potential for catching some cancers earlier, what was that calculation?

DR. WANDA NICHOLSON: Well, you're -- when we think about annual screening, then you are looking at the fact that perhaps you may have detected a cancer earlier.

But the issue remains is whether or not that annual screening correlated with reducing mortality.

So, while you may have a slightly -- you might have a benefit to the annual screening, the harms of the annual screening in terms of false positives and the downstream consequences of that outweigh that potential benefit.

ALI ROGIN: Is there evidence to show that there is no correlation between catching cancers earlier and reduction of mortality?

DR. WANDA NICHOLSON: Well, we do want to catch cancers as early as possible.

I mean, we care about women and we want women to get best care possible.

Again, it's a matter of balancing the benefits and harms.

And when we look across the evidence, as well as our modeling studies, we looked across different strategies.

So we compared screening every other year.

We compared screening every year.

And when you look at that balance of what benefit you may gain with screening annually, compared to those harms, those harms far outweighed those benefits.

ALI ROGIN: The other thing that Dr. Roth brought up was breast density, which, of course, dense breasts are harder to read on mammograms.

Why not make more specific recommendations for dense breasts, for which sometimes MRIs or ultrasounds, secondary screening, is indicated?

DR. WANDA NICHOLSON: Well, we know that up to 50 percent of the women in the U.S. can have dense breasts, so certainly an important group.

The critical question for this population is whether additional imaging with MRI or ultrasound can help women with dense breasts live healthier lives.

So, in other words, should they -- should we recommend MRI?

Should we recommend ultrasound?

How often should we recommend MRI or ultrasound?

So many critical questions there that haven't been answered and for which we need additional science, additional evidence to really be able to make a recommendation.

The task force is calling urgently for more research in this area.

We want researchers to make it a priority.

And in the interim time, for those women with dense breasts with concerns, they should have a one-to-one conversation with their clinician to decide whether, at this point, should they move forward with any additional screening.

ALI ROGIN: And you have to ask about what you mentioned about the lack of answers that are out there.

Certainly, groups like the American College of Radiology, the European Society of Radiology do recommend annual secondary screening for women whose breasts have been shown to be dense.

So what additional evidence is required?

DR. WANDA NICHOLSON: Well, we believe that women need the strongest possible evidence out there to help guide them in their decisions.

And the task force, we have looked - - we looked diligently for evidence to help us to make a recommendation as to how additional screening, additional imaging should be done in women with dense breasts.

And, currently, that evidence just is not there.

We don't want to rely purely on expert opinion.

We really believe that women need that science as the basis and the rationale for what recommendations we make for additional screening.

ALI ROGIN: And I'm just wondering, how do you see the role of the USPSTF in issuing these recommendations in the context of all of the available guidance that's out there for women?

DR. WANDA NICHOLSON: Well, it is true that there are variations in guidance.

I do think that our USPSTF task force recommendations are -- have more similarities with other groups versus differences.

We -- again, we looked across the entire scope of evidence that we had available.

We looked at the comparative benefits and harms.

Whenever we make a recommendation for a preventive service, we really want to look at both sides of the equation.

ALI ROGIN: Dr. Wanda Nicholson, chair of the U.S. Preventive Services Task Force, thank you so much for joining us.

DR. WANDA NICHOLSON: Thank you for having me.