While breast and prostate cancer screenings have often drawn controversy, a new study raises questions about whether their benefits are being exaggerated because some of the most aggressive tumors are being missed.
An article in the Oct. 21 Journal of the American Medical Association challenged the validity of previous studies that claim screening significantly reduces the number of deaths in those two cancers. In turn, a New York Times story reported that day that the American Cancer Society is considering adding cautions to its guidelines on cancer screening and its benefits.
Reviewing U.S. cancer data over the past 20 years, the JAMA authors found that as more men and women follow the prevailing advice and are screened for these cancers, with ever-more sensitive testing, more cancers are found in an early stage.
It sounds good, but the JAMA study said screening finds a larger number of slow-growing cancers, which may not need aggressive treatment, and it still misses the most fast-growing cancers.
This is true in many cases of prostate cancer, for example. Low-risk cancers overtreated with invasive surgery can affect the quality of a man's life without improving the length of his survival.
Catching aggressive breast cancer remains difficult, since it can develop between mammograms, and screening hasn't made a significant reduction in the number of those cases. The JAMA article said that though it is agreed that in breast cancer, screening does save lives, overdiagnosis is a risk: "Many cancers [are] treated as if they were life threatening when they are not." Better treatments are also credited with lowering death rates in breast cancer.
Pittsburgh cancer specialists say men and women should not take these findings as a reason not to be tested, but all agreed that knowing the risks and benefits of screening is important for every patient. They concurred with the study's call for research that would identify which tumors are the most dangerous.
Dr. William Poller, head of breast imaging for West Penn Allegheny Health System, said the JAMA report reached the wrong conclusion about breast cancer screenings. He believes screening can be credited with a decrease in invasive cancers found.
"One could say the decrease is due to the detection of small tumors before [they became life-threatening]," he said. Screening and treatment have been credited with reducing the overall death rate by up to 30 percent.
"No woman has ever complained after the fact that we did a biopsy and it was benign. If we knew in our hearts that it was benign, we'd leave it alone," Dr. Poller said. "Mammography is still the gold standard. It is probably the breast imagers' mistake that we didn't come out and say that mammography isn't 100 percent. It wasn't perfect with dense [tissue] breasts and we've missed cancers that appear in the next year's mammogram."
Survival rates have improved in both cancers, the JAMA article said, but the role of prostate-specific antigen screening for prostate cancer is still under study after two clinical trials reported different results in the March 26 New England Journal of Medicine. More sensitive testing has been found to have "the inability to discriminate between inconsequential disease and disease that will cause serious illness and death," according to the JAMA authors.
Cautions about the benefits of screening come out of a better understanding of cancer in general, said breast surgeon Donald Keenan at The Western Pennsylvania Hospital. No longer is all cancer fatal, for example.
"Once the human genome was cloned, oncology went from cancers and growths to characteristics of masses and tumors ... The future of breast cancer research is separating tumors and classifying them ... to how aggressive they are, based on biology, not based on size."
Change is ahead, according to Dr. Nancy E. Davidson, director of the University of Pittsburgh Cancer Institute, who said the JAMA report illustrates the need for breast cancer and prostate cancer screening now, but better screening in the future.
"Cancer screening is an area of evolution, as in all of medicine," she said. Dr. Davidson has published work on the role of hormones, particularly estrogen, on gene expression and cell growth in breast cancer, and she has led national clinical trials of potential therapies.
"In prostate and breast cancer screening, we do find things, sometimes very serious cancers," she said, adding that tests also detect abnormalities that may not be cancer.
"I look at this as a form of success, that one has this problem. ... We're now at a time where we have to use the power of biology ... to try and sort out which is which, which are the bad ones, which will respond to therapies."
The JAMA report recommended that research and patient care be refocused on differentiating between slow-growing, low-risk cancer and aggressive, high-risk disease. It called for "decision support tools" that make the best, up-to-date knowledge about each cancer available to patients and doctors. For low-risk disease, it called for less aggressive treatments. For high-risk types of these two cancers, the authors called for more money to be spent in developing better prevention, screening and treatments.
Dr. Keenan said he welcomes sharing the JAMA article with patients so they can make informed decisions about their care.
"Health care should always be science-based and evidence-driven," he said. "I think people should know more about how these decisions are made."
Many people might not be weighing the pros and cons of screening, according to Dr. Barnett S. Kramer, associate director for disease prevention at the National Institutes of Health.
For more than a decade, he has warned in professional journals of the need for well-designed research evaluating screening tests.
When asked if men are discussing prostate cancer screening with their doctors, he said, "I don't know how much discussion is going on; some men getting blood tests don't know it's being tested for PSA. That contravenes advice to be sure that men understand the pros and cons of screening."
That applies in breast cancer screening as well, he said.
"There is a growing consensus that there ought to be a discussion about benefits and potential harms. I don't know how frequently that discussion takes place. Physicians have a limited amount of time to discuss with patients. It takes time out of the visits."
Is it too complex a matter for some patients to understand?
"No matter the education level, there are ways to explain the procedures," Dr. Kramer said. "In the case of screening, it may be especially important. Screening takes place in healthy people."
With prostate cancer screening, patients should know that screening is not foolproof, said WPAHS urologist Dr. Ralph J. Miller Jr., director of the Allegheny General Hospital Prostate Center. "The expectation is if you do what you're supposed to do, nothing bad will happen to you. It's not true ... [screening tests] don't guarantee success."
Dr. Otis W. Brawley, chief medical officer of the ACS, was quoted by the New York Times as saying, "The advantages to screening have been exaggerated." On Oct. 21 he issued a clarification of the society's position:
"While the advantages of screening for some cancers have been overstated, there are advantages, especially in the case of breast, colon and cervical cancers. Mammography is effective -- mammograms work and women should continue to get them. Seven clinical trials tell us that screening with mammography and clinical breast exams do reduce risk of breast cancer death. This test is beneficial in that it saves lives, but it is not perfect. It can miss cancers that need treatment, and in some cases finds disease that does not need treatment. ...
"The American Cancer Society stands by its recommendation that women age 40 and over should receive annual mammography, and women at high risk should talk with their doctors about when screening should begin based on their family history."
The statement confirmed the society's position on prostate screenings:
"Since 1997 the American Cancer Society has recommended that men talk to their doctor and make an informed decision about whether or not prostate cancer early detection testing is right for them. This recommendation also still stands."
Jill Daly can be reached at firstname.lastname@example.org or 412-263-1596.