Cancer: The Myths of Early Detection

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http://www.cbc.ca/news/indepth/background/cancer_earlydetection1.html

 

Cancer: The Myths of Early Detection

 

CBC News Online | May 26, 2003 Some influential cancer researchers are

questioning the conventional wisdom that finding a cancer early will improve the

chance of survival.

 

In a special three-part series, CBC Television and CBC Radio look at:

Part 1: the controversy over whether early detection is an outdated idea for

some cancers

Part 2: the value and potential harm of screening tests that detect disease

in people who don't show any symptoms

Part 3: how researchers are using new technologies to detect cancer earlier

and determine which ones are most likely to kill

 

 

 

The Myths of Early Detection

 

Detecting cancer early could save your life — maybe.

 

Cancer prevention advertisement Conventional wisdom says the sooner cancer is

found and treated, the more likely you are to beat the disease. For 50 years,

cancer societies and patient advocacy groups have pushed the empowering message.

Now a growing number of influential cancer researchers are questioning the value

of early screening, saying it is outdated, misleading and may not be saving as

many lives as we thought.

 

The problem is, cancer isn't simple. In same cases, our fate could be sealed by

the time cancer is found, no matter how early. Other cancers aren't harmful

because they never grow large enough during a patient's lifetime to cause

medical problems. Biostatistician Dr. Don Berry of the MD Anderson Cancer Center

in Houston studies cancer mortality. He says the early detection evidence isn't

clear yet for some cancers and some tests.

 

Dr. Don Berry " We don't know that it's beneficial to detect the first cells

that are cancerous, " says Berry. " The cat may be out of the bag almost

immediately. "

 

Traditionally, cancer cells were viewed as normal cells that went out of

control, dividing and invading normal tissue, and eventually killing the

patient. Now scientists realize different types of cancers not only behave

differently, but one individual's cancer behaves differently from another

person's cancer.

 

Take breast cancer, for example. At one time, scientists thought breast cancers

grew very slowly, in an orderly manner and only left the breast and spread or

metastasize to the rest of the body late in the disease. This scenario favoured

the logic of early detection, which often doesn't work as well for cancer that

spreads early in the disease.

 

" What we've come to learn now from the most recent data is that finding a breast

cancer earlier may be a good thing for an individual woman, but it may not be, "

says Dr. Barron Lerner, an internist in Manhattan, a breast cancer researcher

and author of The Breast Cancer Wars. " Getting this more nuanced message, this

more subtle message across against a background in which early detection has

been stressed over and over is what's very difficult. "

 

According to Berry, every cancer behaves differently depending on its genetic

characteristics.

 

Dr. Barry Kramer is editor of the Journal of the National Cancer Institute and

director of disease prevention for the National Institutes of Health in

Bethesda, Maryland. He uses an animal analogy to describe different cancerous

tumours.

 

" Just like turtles, there are some cancers that grow extremely slowly and may

never harm someone had they not been detected, " says Kramer. " There are birds

that fly very quickly, and they're the ones that metastasize early on, spread to

other organs before you get a chance to grab them. " " Then there are the

intermediate ones, the bears. The bears are those that could escape but it takes

them a little longer to escape. The problem is with any given type of cancer, we

don't know how many bears there, how many turtles there are and how many birds

there are. "

 

Overdiagnosis and Overtreatment

 

Since doctors don't know what they're looking for, they screen for cancer in

everyone. If cancer is found, it's treated. People with slow-growing cancers

that might never cause a medical problem become cancer patients, sometimes

leading to overdiagnosis and overtreatment.

 

" I think we're accustomed to being very aggressive when it comes to cancer,

doing more instead of less, " says Lerner. " Treat the many to save the few. Once

you begin the process of looking for something, you may end up minus a prostate

or a breast. "

 

Kramer says overdiagnosis is potentially tragic. " If you detect and treat a

cancer that never would have harmed a patient in the first place then you are

likely to confer harm, " he says. The harm can come from complications after

surgery, the long-term health effects from radiation and chemotherapy, such as

causing second cancers, and the side-effects of chemo.

 

Overdiagnosis is probably the rule, not the exception, according to Kramer.

 

 

Animation of cancer cells dividing For some women who've benefited from early

detection by breast self-examinations or mammograms, the debate is irrelevant.

Gail Alexander was 49 when mammography detected her breast cancer three years

ago, and doctors tell her she is now cancer free.

 

" I do know that by doing both of these tests my life was saved, " says Alexander.

" My surgeon told me if I didn't have that mammogram I might not be here in two

or three years. " Other breast cancer survivors say if their cancers weren't

detected early then they would have been sicker and required more invasive

surgery. It depends on whether someone's cancer is a turtle, bear or bird.

 

For breast self-exams, Lerner says by the time someone can feel a lump, it has

likely been sitting there for at least six years, which isn't really early

detection. If it was a cancer that's likely to spread, it probably would have.

 

Kramer notes averting a single breast cancer death would require mammograms on

1,200 healthy women a year for 12 years. " It angers me because whether it saved

one in 20,000 women, if we can save one life by doing monthly breast self-exams

and yearly mammograms to me it's important and it saved my life, " says

Alexander.

 

It's hard to argue with Alexander's anecdotal evidence, says Dr. Verna Mai,

director of screening programs for Cancer Care Ontario. For Mai, the potential

benefits of screening usually outweigh the risks.

 

Biostatistician Dr. Berry says researchers ought to be evaluating the value of

all medical techniques, include screening tests. There is strong evidence that

early detection helps for cervical cancer and colon cancer. The problem is,

we've been sold the message for all cancers.

 

The Canadian Cancer Society recognizes early detection doesn't always save

lives. The society recommends some screens, such as pap smears, as well as

mammograms and prostate tests for people over 50.

 

Dr. Barb Whylie " We actually believe that people should look for their cancers,

and to try to find them as early as possible, " says Dr. Barb Whylie, executive

director of the Canadian Cancer Society. " Part of the reason for this is that we

really believe it's important that people are empowered to take whatever control

they can for their own health. "

 

Lerner says before healthy people agree to cancer screening, they need to know

that finding cancer early is no guarantee of a good outcome. The cancer could be

a bird that's programmed to kill despite all medical efforts.

 

Many cancer specialists agree and say doctors should be speaking more honestly

with their patients about the benefits, limits and risks of early detection to

balance the hope and science.

 

 

 

Prostate Cancer Screening

 

Screening tests are given to healthy people who have no reason to believe

they're sick. Medical researchers are wondering if some of the tests are doing

more harm than good.

 

The pap test for cervical cancer is an example of a widely successful test. It

finds potentially dangerous cells early enough to save lives.

 

Dr. Verna Mai " Some screening tests like the pap tests actually are detecting

changes that are pre-cancerous, " said Dr. Verna Mai, director of screening

programs for Cancer Care Ontario. " So before the cell changes move to a state

where they're a cancer, they're being detected by pap testing. "

 

On the other hand, the value of the PSA (prostate specific antigen) screening

test is less certain. The simple blood test looks for elevated levels of a

certain antigen that can signal cancer in the prostate, a small, shiny round

organ located below the bladder and in front of the rectum in men.

 

PSA test Both the Canadian Cancer Society and the Canadian Prostate Cancer

Network run public service announcements advising men over age 50 to talk to

their doctors about PSA testing.

 

The PSA test is a controversial screening tool for cancer; some provinces pay

for it, while others don't. Like all tests, there are false positive and false

negative results.

 

A public service announcement encourages men over 50 to get checked for signs

of prostate cancer The prostate cancer test is right about one in three times,

according to Dr. John Trachtenberg, director of the prostate centre at Princess

Margaret Hospital in Toronto. Trachtenberg supports testing men over 50, saying

it has little downside.

 

Many agree the PSA is good at finding cancers. The debate is whether it finds

the right cancers – those that are likely to grow and spread, rather than remain

small and harmless.

 

As more Canadian men had the test, the incidence of prostate cancer in Canada

rose:

92 cases per 100,000 in 1989

118 cases per 100,000 in 1999

During the 10-year period, the death rate did not decline dramatically. Prostate

cancer deaths did fall by 10 per cent, but some attribute the decline to better

treatments and not just earlier detection.

 

For biostatistican Dr. Don Berry of the MD Anderson Cancer Center in Houston,

the mortality statistics suggest the PSA test is overdiagnosing prostate cancer.

 

" One of the harms is finding cancer, " says Berry. " People don't like it when I

say that. " When doctors find cancer, they tend to want to treat it, even though

they don't always know whether it is a cancer they need to worry about.

 

Pathologists look for pre-cancerous changes in a pap test Berry refuses to get

a PSA test himself. Since prostate cancer can be very slow-growing, he feels

it's unlikely to kill him. On the other hand, prostate surgery is one of the

most common treatments and it can result in harm.

 

One study showed almost 60 per cent of patients who had their prostates removed

had problems getting an erection one year after surgery.

 

" Removing the prostate is associated with a very high incidence of incontinence

and impotence, neither of which I want to have, " says Berry. " I'll do lots of

things to avoid having it, including living with the possibility unbeknownst to

me, that I have prostate cancer. "

 

Leon Fitzgerald Leon Fitzgerald of Halifax did have prostate cancer. Two years

ago, Fitzgerald was 55 and thought he was perfectly healthy. Then Fitzgerald's

doctor did a PSA blood test. For Fitzgerald and his wife, the risk of impotence

and incontinence was overshadowed by their fear of prostate cancer. He opted for

prostate surgery.

 

" I could have done surgery, I could have done radiation, " said Fitzgerald. " I

took the surgery and it was my choice, because I wanted to have it removed, I

wanted to be around to deal with it. "

 

" I think that by having the PSA test done, it saved my life for sure, " he adds.

Many men's advocacy groups agree.

 

Another option is called " watchful waiting. " A PSA test may show elevated

antigen levels, but the levels don't always mean cancer. " What we've found is

most men with prostate cancer will live eight to 10 years without any problems, "

says Halifax urologist Dr. David Bell.

 

Clinical research is underway in Canada, the U.S. and Europe to determine the

real value of PSA testing. The results are expected in a few years. Until then,

the Canadian Cancer Society is reluctant to recommend for or against regular

testing.

 

" Until we actually have some sort of trial evidence, we can't say that prostate

screening reduces mortality, " says Mai of Cancer Care Ontario.

 

In Canada, the current recommendation is men over 50 should talk with their

doctors about PSA testing. Without definitive evidence, the message seems to be

weigh the pros and cons and make a personal decision.

 

 

Telling the Lethal Cancers from the Harmless Ones

 

As a real estate agent, Andrew Marshall has to work hard while the market's hot.

To take six weeks off right now to have surgery on his prostate would be costly

and risky.

 

Andrew Marshall Marshall has prostate cancer. But he's not doing anything about

it, and he has his doctor's blessing.

 

" I felt very good about that because I personally felt that's the way I should

go, " he says. " But between caring family and other advice, they always say with

cancer get rid of it and don't worry about it, so I'm very comfortable with it. "

 

Marshall's doctors are doing something called " watchful waiting. " They're just

going to monitor him to see if he has the type of prostate cancer that grows

very slowly.

 

Dr. Barry Kramer, editor of the Journal of the National Cancer Institute in

Bethesda, explains that it's hard to predict how an individual's cancer will

behave, and detecting it early is no guarantee.

 

" Some of the patients will die quickly, unfortunately, because they have rapidly

moving cancer that metastasizes very early and others will be much slower

growing, " he says. " That's why most physicians are extremely reluctant to try to

predict for patients exactly how long they can expect to live. They can't make

accurate predictions. "

 

Marshall goes for regular testing. If his levels start to go up, it may mean the

cancer is growing, and it's time to treat it.

 

For other cancers, it's harder for doctors to tell whether they're dealing with

an aggressive or lethargic tumour, so they treat them all, often with invasive

or toxic therapies.

 

But a new approach to cancer diagnosis may change all that.

 

Emmanuel Petricoin Emmanuel Petricoin uses robotic technology to look for

cancer biomarkers, a biological signal that will say, " Hey, this is cancer. "

 

Petricoin's lab in Bethesda is comparing blood samples of healthy women with

women diagnosed with ovarian cancer. He's trying to see if his equipment can

tell the cancerous patients from the non-cancerous patients.

 

" What really got our attention was when we were able to, with 100 per cent

accuracy in a small study set, determine all stage-one ovarian cancer cases from

a drop of blood, " says Petricoin. " Now granted, this was only on a few dozen

patients, but it got all of them correct. "

 

If larger studies verify those findings, it will be a huge advance in diagnosing

ovarian cancer, a cancer for that has no good diagnostic test. But the potential

goes further than just diagnosis.

 

Proteomics, the leading edge of cancer diagnosis, could help distinguish between

an aggressive tumour (one that's likely to metastasize and kill) and a tumour

that will remain harmless.

 

Columbia Hospital Internist Dr. Barron Lerner Columbia Hospital Internist Dr.

Barron Lerner says in the future, the genetic makeup of a cancer will be more

important than how early it's detected.

 

" Now we can begin to look at the genetic makeup of these cancers, try to

correlate that to the outcomes of patients and possibly in the near future be

able, when a woman is diagnosed with breast cancer or a man with prostate

cancer, to say, 'Hey, this is a bad looking cancer. You need very aggressive

treatment. Or this cancer actually is likely to have a good outcome if we can

hold back a little bit,' " says Lerner.

 

Once scientists know the genetic signature of a cancer, they can develop drugs

designed to target those specific genes or proteins. Treatment would be tailored

to a patient's specific type of cancer.

 

Herceptin for breast cancer and Gleevac for a rare type of leukemia are examples

of therapies that already do that. They're only given to patients whose tumours

express certain proteins. The treatments work well for those patients.

 

" The protein pathways and the circuitry of the cell actually dictate whether a

person is really going to respond to the therapy, " says Petricoin. " So we think

that proteomics will actually be the revolution that takes patient-tailored

therapy, rational drug design, to the clinic. "

 

Skeptics say these DNA chips may be too expensive and difficult to use in the

average laboratory.

 

But advocates say the technology will get simpler.

 

And there will be other savings: fewer patients will be treated with surgery,

chemotherapy and radiation if their cancers are deemed non-invasive.

 

They'll be more like Andrew Marshall: living with cancer and not with the

side-effects of treating it.

 

 

 

 

 

 

 

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