Two big studies suggest possible new ways to screen healthy people for cervical or prostate cancers, but a third disappointed those hoping for a way to detect early signs of deadly ovarian tumors.
Researchers found:
—For women 30 and over, a test for the virus, HPV,
is better than a Pap smear for predicting cervical cancer risk, and those who
test negative on both can safely wait three years to be screened again.
—A single PSA blood test at ages 44 to 50 might
help predict a man's risk of developing advanced prostate cancer or dying of it
up to 30 years later. The PSA test is notoriously unreliable, but using it this
way separates men who need a close watch from those who are so low-risk that
they can skip testing for five years or more.
—Screening women with no symptoms for ovarian
cancer with a blood test and an ultrasound exam is harmful. It didn't prevent
deaths and led to thousands of false alarms, unneeded surgeries and serious
complications.
The last study is a warning to people who get
screening tests that aren't recommended, or who question whether screening can
ever hurt.
"The answer is, it could hurt a lot,"
said Dr. Allen Lichter, chief executive of the American Society of Clinical
Oncology. The group published these and 4,000 other studies Wednesday, ahead of
its annual meeting next month.
Cervical cancer is easy to prevent. It's very
slow-growing and screening finds precancerous cells and allows early treatment.
The new study was the first big one to examine a newer screening tool, HPV
tests, with or without Pap smears in routine practice.
For a Pap test, cells scraped from the cervix, the
gateway to the uterus, are checked under a microscope. But this can miss
problems or raise false alarms.
HPV tests detect the human papillomavirus, which
causes most cases of cervical cancer. But HPV is "the common cold" of
the nether regions — most sexually active young people have been exposed to it,
said Debbie Saslow, the American Cancer Society's director of breast and
gynecologic cancer. Most infections go away on their own; they're only a cancer
risk when they last a year or more.
Younger women tend to have short-term infections,
so Pap tests are a better way to screen them. HPV tests are approved as an
option along with Paps for women 30 and older, and the cancer society says that
if a woman tests negative on both, she can wait three years to be screened
again. Few take this advice, though.
"Women still want their annual Pap and doctors
still want to give them," and think it's rationing care to test less
often, Saslow said.
The new study gives "very, very solid
support" for screening less often, Lichter said.
Hormuzd Katki of the National Cancer Institute
studied more than 330,000 women getting HPV and Pap tests through Kaiser
Permanente Northern California for five years.
Only about three out of 100,000 women each year
developed cervical cancer after negative HPV and Pap tests. HPV tests were
twice as good as Paps for predicting risk. Adding a Pap after a negative HPV
test did little to improve risk prediction.
However, if an HPV test was positive, a Pap test
helped confirm or rule out the need for follow-up.
The study didn't look at the downside of HPV
testing — how many false alarms and needless procedures it triggered. HPV tests
cost $80 to $100 compared to $20 to $40 for Paps.
The prostate study sought a better way to use PSA
tests, which are troublesome because PSA can be high for many reasons besides
cancer, and doctors don't know which cancers need treatment or whether
screening saves lives. Most groups don't recommend PSA tests, but most men over
50 get them anyway.
The new study "is not going to end the
controversy, but it suggests a very interesting middle ground," Lichter
said.
Researchers at Memorial Sloan-Kettering Cancer
Center in New York used stored blood samples that 12,000 Swedish men gave for a
heart study decades ago, when most were 44 to 50 years old. They also had
second samples from some of them six years later, and samples from other
60-year-old men.
Looking 27 years later, researchers saw that 44
percent of cancer deaths occurred in men whose initial PSAs had been in the top
10 percent when they were 44 to 50 years old.
Conversely, scoring below the median meant very
little cancer risk years later.
"They're identifying a group of guys who don't
need to be screened, or need to be screened less often," said Dr. Otis
Brawley, the cancer society's chief medical officer.
The results are "provocative," but this
type of study can't prove that screening prevents deaths, said Dr. Matthew R.
Smith of the Massachusetts General Hospital Cancer Center. Few of the Swedish
men were treated for prostate cancer as most men are today, which can affect
survival.
The National Cancer Institute, the Swedish Cancer
Society and several foundations paid for the work, and one researcher holds
patents for two PSA-related tests.
Baseline PSA tests for men in their 40s can't be
recommended yet, Brawley said. The cancer society says men should be informed
of the risks and benefits of PSA tests starting at age 50, and sooner for
blacks and those with family history of prostate cancer.
The government-funded ovarian cancer study involved
nearly 80,000 women. Half were screened annually with an ultrasound for four
years and a blood test for six years. The blood test looked for CA-125, a
substance often elevated in ovarian cancer.
After 13 years, there were no major differences in
ovarian cancers found or deaths from the disease. Screening found only 212
cancers while giving 3,285 false alarms that led to 1,080 unneeded biopsy
surgeries and 163 serious complications.
"So many people say 'how can cancer screening
be harmful?' This thing documents it," Brawley said.
The results don't apply to using these tests on women
with symptoms of ovarian cancer or abnormal physical exams. That's still the
best way to check for ovarian cancer in those cases.
Copyright 2011 The Associated Press.
