Nov. 18, 2009 -- New guidelines saying women between the ages of 40 and 50 should not receive mammograms to screen for breast cancer have met a groundswell of rejection from many medical centers, breast cancer survivors and numerous doctors -- some of whom have advised their patients to ignore the recommendation.

The American Cancer Society and the American College of Obstetrics and Gynecology are among the many groups that supported the old guidelines and have stood firmly by them since the United States Preventive Services Task Force released its new recommendations Monday evening.

The USPSTF, a panel of independent medical experts, said it was recommending against annual mammograms for women between the ages of 40 and 49, saying the risks outweighed the benefits from earlier screening. That announcement, which goes against a trend of recommending increased screening by cancer agencies, has left many confused.

Meanwhile, doctors' offices and hospitals have been fielding calls from women wanting to know what these new guidelines will mean for them.

One of these calls came not from a woman concerned about getting breast cancer but one who has already had it. Beth Thompson, 44, a mother of four who lives in the suburbs of Baltimore, Md., was first diagnosed with breast cancer following a mammogram at the age of 40.

"I had no risk factors and no family history," Thompson told ABCNews.com. "Under the new guidelines I wouldn't be screened. That's why I'm so upset about this. I firmly believe I would not be here today if I had not had a screening mammogram at 40."

Thompson explained that in removing the tumor detected by the mammogram, doctors found a faster-growing one underneath, one that would not have been found until it became a palpable lump.

"It really makes me shudder to think of what a different situation I would have been in if that were the case," she said, explaining that she needed four surgeries, four rounds of chemotherapy and took Herceptin, an adjuvant for an aggressive form of breast cancer, for a year.

"That's the treatment that I needed even for an early-stage cancer," Thompson said. "There's just no reason that I would have been screened and no way that it would have been found at the time, except for mammography."

According to most medical centers that ABC News has heard from, the new screening guidelines will not be followed. M.D. Anderson, the Mayo Clinic, Baylor College of Medicine and Fox Chase Cancer Center were among many hospitals that said they are sticking with the current guidelines, recommended by the American Cancer Society.

In recent months, some sentiment has arisen opposing increased screening. A study released in September brought to light some of the potential risks of a false positive. While efforts have been made to increase cancer screening, many patients are unaware of the potential consequences of a false positive, including unnecessary anxiety, testing and possibly treatment.

"[Some] women don't understand how screening can cause problems," said Dr. Bob Crittenden, an associate professor in family medicine at the University of Washington. "Personally, I think this is symptomatic of many in people in medicine promising good health if you get screened. As we know with PSAs and other screenings of asymptomatic people, we have only a few things we can do that actually help extend life and then usually only marginally."

Crittenden explained that in his own practice, patients are screened if they would like before age 50 and screenings are strongly encouraged after that age.

Several family doctors contacted by ABC News said the recommendations reflect some of the sentiment against screenings because of the possibility of unnecessary treatments, and expressed hopes that they will lead to more open conversations about mammograms and cancer screening with patients.

Sources of Medical Opposition

Dr. Gary Lyman, a breast cancer oncologist at Duke University who researches comparative effectiveness, says guidelines like those issued by the USPSTF may cause a great deal of harm.

"This is a reversal of the position they took in their previous recommendations, and this flies in the face of previous guidelines from other groups in the U.S.," he said. "[While] the risk of breast cancer is less in the younger age group, 40 to 50, mammograms save lives in those age groups."

Lyman said his primary criticism is that in between the last set of screening guidelines in 2002 and the current ones, only one study has come out in the area, and it did nothing to change what doctors know about mammograms.

"I'm puzzled why, when the evidence hasn't really changed, when the estimate in benefit and risk hasn't really changed, why they reversed their position," he said.

Lyman said he was also worried about potential confusion among women over 50, since under the new guidelines they are being told to get screened every other year, while previously they had been told to get screened every year.

"I don't know if we know that's going to cause harm or not," he said. "What I'm worried about the most, however, is confusion on the part of women and their physicians that may make them question whether mammograms will do anything."

His concerns were borne out in at least one New York hospital on Tuesday.

"I spoke to our breast imaging department today and they said that the 'no-show' rate doubled today," said Dr. Susan K. Boolbol, the Chief of Breast Surgery at Beth Israel Medical Center in New York. "That means that twice as many patients today decided not to show for their mammogram appointment. That is a very concerning rate. We will monitor this to see if it continues."

But Boolbol said she is also concerned that "controversies such as these really create a feeling of mistrust for the medical community at large."

Lyman said the benefits of mammography have been clear, particularly since insurers and Medicare began reimbursing for them, noting that mortality rates have fallen by 25 percent since then.

"I can't say all that's due to mammography, but it's pretty clear that part of that and maybe most of that is due to early detection with routine mammographic screening," he said.

But he agrees with Boolbol about the potential for mistrust, noting that screening rates have fallen in the past few years.

"I'm concerned again, with all this confusion, that women may stop getting their mammograms regularly. We may not know the effect of that [in terms of mortality] for another 10 to 15 years," Lyman said.

While many have said the new recommendations are part of a bid to lower medical costs, Lyman said he does not believe there was an economic motive.

Instead, he said, the issue could be that the panel does not include a breast cancer specialist.

"There's no breast cancer expertise on that panel, and I think it's hard to develop guidelines with the data as it is without understanding breast cancer," he said. "It's certainly not a change in the evidence. Something else is at work."

Breast Cancer Screening Recommendations 'Devalue' Lives, Survivor Says

While false positives may create problems for some patients, many seem to feel that those are outweighed by the deaths that can result if the screening is not done, something that will present a challenge to any desire to change screening guidelines.

"At the Methodist Breast Center, we diagnose and/or treat about 500 patients with breast cancer every year," said Dr. Luz Venta, medical director of the Methodist Breast Center in Houston and fellow of the Society of Breast Imaging, in a statement. "And about 21 percent of these are women under age 50. Should these women be sent away and told the cost of screening for breast cancer is not justified in the number of lives that can be saved?"

That sentiment was echoed by many, some of them survivors of breast cancer themselves, who flooded the message boards of breast cancer groups like breastcancer.org and the Susan Love Foundation to protest the new guidelines.

Thompson, whose sentiments run along those same lines, said she worries about getting her own daughters, the oldest of whom is in her teens, proper screening when they reach the right age, and is concerned that future recommendations might change how soon they get screened.

"I will move heaven and earth to have them screened at 30," said Thompson, affirming the recommendation that women with a first-degree relative with breast cancer get screened 10 years before cancer first appeared in that relative.

But Thompson, reflecting the sentiments of other survivors of breast cancer, also said she worries that any recommendation for screening that would have excluded her also devalues the lives of other potential breast cancer survivors.

"It's disheartening to hear the new guidelines, when they talk about the few lives that are saved," she said. "It's hard not to feel a little devalued by that."