Breast cancer:

Mammography has been one of the most successful cancer-screening tests and is widely accepted based on studies showing it saves lives. The American Cancer Society also lists more than 20 imaging technologies that now can be used for breast-cancer detection, such as sonograms, which often are combined with mammography.

Mammography still isn't as good as doctors want it to be. Current guidelines recommend that women of average risk start mammography at age 40, in part because mammography doesn't work very well on denser breasts, which are more common in younger women. Mammography also misses a lot of cancers in older women. A study last year found that almost 40 percent of women with late-stage breast cancer had a negative mammogram one to three years prior to their diagnosis.

There is some hope that so-called digital mammography, which uses detectors similar to those found in digital cameras, will be able to detect breast cancer better than the standard screen-film mammography. The technology is available at some medical centers, and a large trial on the subject is expected to publish results this year.

MRI, or magnetic resonance imaging, has been shown to detect more tumors than mammograms, but also comes with a high false-positive rate; MRIs are recommended only for women who are at high risk because of a family or personal history of breast cancer.

One new test generating excitement is a more precise mammogram called tomosynthesis breast imaging. The tomosynthesis machine takes more pictures of the breast, from many more angles and much more quickly, than a conventional mammogram. Pilot studies conducted at Massachusetts General Hospital in Boston indicate the test sees abnormalities more clearly than the standard mammogram, even in younger women. The hospital still has more research to conduct before the test can be made widely available.

Other tests, such as positron emission tomography (PET) scans, X-ray computer tomography (CT) and novel ultrasound methods such as 3-D and Doppler, have shown some promise and are available at many hospitals and clinics. More research needs to be done before they could be recommended for widespread screening.

Bottom line: Until more trial results are published and more work is done on tomosynthesis, most women of average risk of getting breast cancer are advised to get standard mammograms.

Colorectal cancer:

Effective screening tests already exist for colorectal cancer. Unlike virtually every other area of screening, patients have a range of choices that are endorsed by the American Cancer Society. The society recommends annual fecal occult blood tests; flexible sigmoidoscopy every five years; annual FOBT plus flexible sigmoidoscopy every five years; double contrast barium enema every five years; or colonoscopy every 10 years.

Fewer than half of those recommended for regular screening - men and women over 50 - do so. That is partly out of an aversion to the various procedures, which can involve enemas, anesthesia and handling of stool samples.

CT colonography, also known as virtual colonoscopy, has received a fair amount of attention of late; early tests indicate the test may be more effective in picking up certain lesions than standard colonoscopies. There is hope that people will be more willing to use it since it is faster and less uncomfortable than a standard colonoscopy and doesn't require anesthesia. Downsides: It still requires bowel preparation and, if any polyps are found, a follow-up standard colonoscopy to remove them. While the test still isn't widely recommended, that could change with results from a major trial set to begin this year.

In addition, private companies are creating tests that are far less invasive. International Medical Innovations Inc. has developed ColorectAlert, a low-cost screening test that identifies the presence of sugars in a sample of rectal mucus that can be associated with cancer. Because the sugars can be associated with benign conditions as well, the test isn't used to replace a colonoscopy but to signal who should go for further testing.

Exact Sciences of Marlborough, Mass., has developed a test that screens DNA extracted from a stool sample for gene alterations that can suggest cancer. The company sells the test for $795.

Bottom line: The cancer society and U.S. Preventive Services Task Force both have called virtual colonoscopy promising but don't recommend it for general screening, saying there isn't enough evidence yet for it, or for DNA stool tests.

For patients who do choose the virtual route, it is important to ask what kind of machine is involved, since not all procedures are equal. A 2003 study in the New England Journal of Medicine found that a 3-D version of the machine - which isn't the same as that used in hundreds of screening venues - worked just as well as regular colonoscopy.

Lung cancer:

Lung cancer frequently doesn't have any symptoms until it is advanced and difficult to treat. The traditional way to detect it has been with an X-ray.

Now, there is a test - spiral CT scan - that seems to find the cancer much earlier, when surgery still is an option. The screen is controversial, both because it is expensive and because the machines are so powerful they often pick up nodules that aren't cancer at all. Patients can get a spiral CT at various sites, including some malls. The cost is around $300, and insurance generally doesn't cover it.

In a study at the Mayo Clinic in Rochester, Minn., 50 percent of heavy, long-term smokers over 50 who were given spiral CT scans were found to have at least one nodule. In most cases, however, doctors couldn't tell if the nodule was malignant or benign. Among the lung operations done as a result of those scans, 17 percent turned up benign conditions, meaning these people unnecessarily faced the risks of major complications such as a collapsed lung or death.

Other studies have demonstrated the effectiveness of spiral CT in finding lung cancer earlier.

Bottom line: While it probably will be five years before learning the outcome of a large 50,000-person trial comparing spiral CT and chest X-rays, the American Cancer Society acknowledges that early studies look promising. Patients are advised to first discuss the test with a doctor, and if taking the test, to do it in an experienced center capable of diagnosis and follow-up.

Oral cancer:

Oral cancer kills more than 8,000 people a year and is the sixth-leading form of cancer death, but it often isn't detected before it is plainly visible to the naked eye. ''Oral-cancer screening is at a barbaric stage,'' says Douglas Burkett, chairman, chief executive and president of Zila Inc., a Phoenix company working on new screening devices.

Even visual screens aren't performed as often as they should be; people over 40, and anyone who smokes or drinks more than one drink a day may be at greater risk for the disease.

Zila has a product on the market called ViziLite, a $20 lightstick that illuminates abnormalities in someone's mouth after the patient rinses with a special solution. Dentists charge around $45 for the exam, Burkett says. ViziLite does turns up a large number of benign conditions that can resemble cancer. A second product in the works called OraTest shows promise for a higher accuracy rate, Burkett says.

Bottom line: Even though there is the risk of false positives with emerging oral-cancer screens, the ramifications are less serious than with some other cancers. Biopsies for oral cancer are noninvasive, involving a swipe of cells from inside the mouth.

Prostate cancer:

When it comes to controversies about screening tests, one of the loudest and longest has been over the PSA, or prostate specific antigen, blood test. Used widely since the 1980s, it looks for elevated levels of certain substances that could indicate early cancer. More and more experts lately are arguing against it, contending it doesn't reliably indicate how much cancer someone has or how serious it may be. Many men would prefer not to have an uncomfortable biopsy without greater assurance that it is called for. Even a biopsy may not accurately assess the cancer, because there is no guidance from a PSA test on precisely where to look. Severity of the cancer is an important consideration, since patients who opt for treatment face the risk of side effects including impotence and urinary and bowel problems.

Also, there are no large clinical trials that conclusively demonstrate that having a PSA test helps reduce a man's chances of dying from cancer.

There have been some efforts to refine the PSA test, and there are at least six different variations of the test now available that aim to be more accurate, including free PSA, which measures the percentage of PSA that isn't bound to proteins in the blood, and PSA velocity, which looks for change in several readings rather than a single PSA test.

Some groups around the country are searching for markers in blood, saliva and urine that might indicate when prostate cancer is present. Efforts are under way to improve imaging of the prostate using MRIs, ultrasound and other technologies. These methods ''are not ready for prime time yet,'' says Philip Kantoff, director of the prostate-cancer program at Dana-Farber Cancer Institute in Boston. ''I wouldn't throw out the PSA test yet.''

Bottom line: The consensus on whether to take the PSA - or one of the variations of it - is to discuss the potential benefits and possible drawbacks with a doctor before deciding. Personal choice, family history and an individual's risk factors will play a big role. The American Cancer Society also says men should be offered the option of a digital rectal exam, which can help detect cancer.

Who's who in the cancer community and what they're tested for

Here are the tests that some prominent figures in the cancer community have chosen to undergo.

Their decisions do not necessarily reflect the opinions of the organizations they are associated with.

Lance Armstrong

Founder, Lance Armstrong Foundation, testicular-cancer survivor, six-time Tour de France winner

Screening tests: Blood test four times a year to measure HCG; elevated levels might indicate cancer had recurred.

Comment: When asked if he gets other cancer screening tests, such as PSA, Mr. Armstrong said, ''No. Not yet. I'm 33.''

Lee Hartwell

2001 Nobel laureate; president and director Fred Hutchinson Cancer Research Center, Seattle

Screening tests: Colonoscopy every five years, and an annual digital rectal exam. No PSA test.

Comment: He will forgo PSA testing ''until we develop a more-refined prostate-cancer test that distinguishes slow-growing tumors from those that are aggressive.''

Jean Sachs

Executive director of Living Beyond Breast Cancer, a patient advocacy and education group

Screening tests: Annual Pap smear, mammogram.

Comment: Sachs had her first mammogram at age 35 because her mother was diagnosed with breast cancer, putting Ms. Sachs at higher risk.

Edward J. Benz Jr

President and chief executive officer, Dana-Farber Cancer Institute, Boston

Screening tests: A PSA test, digital rectal exam and check for skin cancer during annual physical exams. Colonoscopy every three years.

Comment: Benz has a family history of polyps, which can potentially develop into colon cancer, as well as prostate cancer.

Andrew von Eschenbach

Director of the National Cancer Institute

Screening tests: Annual PSA blood test and dermatological exam to look for skin cancer; colonoscopy every three years.

Comment: Von Eschenbach is a two-time cancer survivor - of melanoma and prostate cancer - and is thus at higher risk. ''Early detection saved my life,'' he says.

Ellen Stovall

President and CEO National Coalition for Cancer Survivorship, an advocacy and educational group for cancer survivors

Screening tests: Annual mammogram, Pap smear, fecal occult blood test, breast self-exam, chest x-ray, sonogram of the thyroid gland, urinalysis and blood test. Colonoscopy every three years.

Comment: Stovall is the survivor of two diagnoses of Hodgkin's disease and has a family history of noncancerous polyps. She underwent radiation, which puts her at a higher risk for future cancers.

David H. Johnson

Deputy director, Vanderbilt-Ingram Cancer Center; president, American Society of Clinical Oncology

Screening tests: Colonoscopy once every three years. No PSA test.

Comment: Johnson says there are disparate recommendations on PSA from various medical societies. He also notes that while he is a nonsmoker, if he were a former or current smoker, ''I would consider undergoing a spiral CT'' to screen for lung cancer.