Minnesota Academy of Family Physicians

Screening for Cancer: What Doctors Do and Cannot Do
- An Update from the Minnesota Academy of Family Physicians -

February 24, 2009

Most of us know someone who has been affected by cancer, and if we don’t, we read about it or hear stories in the news. Because people want to be proactive and protect their health, family physicians will tell you, that patients often come into their doctor’s office and say something similar to this , “Screen me for every kind of cancer, doc. I want to know if I have IT.”

“What patients don’t realize is that each type of cancer is unique and often very different from all other types,” said Glenn Nemec, a family physician with The Monticello Clinic in Monticello, Minnesota. “It’s not just ONE disease, it’s hundreds of diseases.”

Screening is a means of detecting disease early in people who have no symptoms. Family physicians are able to successfully screen for a few specific types of cancer that share certain characteristics. These characteristics are 1) that the cancer has a long pre-cancerous or early cancer phase, 2) that there is an accurate test to identify that phase, and 3) that treatment options are effective during the phase.

“This means doctors cannot and do not screen for cancers that are fast to grow or spread, cancers that have no reliable test to find them and cancers that have no highly effective treatment,” said Dr. Nemec. Positive results from a screening are not typically used to diagnose cancer, but they identify persons at an increased risk for the presence of cancer who need further evaluation.

There are four cancers for which we can very effectively screen. One type is cervical cancer. This cancer has a long pre-cancer phase called dysplasia. The accurate test to detect it is called a pap smear. Once detected, there are various ways to remove the dysplasia tissue. Recommendations for pap smears have changed recently and are more complicated. Patients should talk to their doctor about how often they should be tested. Earlier diagnosis of cervical cancer does produce better survival rates and treatment is extremely effective when all recommendations are followed.

A second type of cancer that can be screened for is breast cancer. This cancer has a long early cancer phase before it spreads. The accurate test for this is a combination of a physician exam and mammography. Dr. Nemec points out that some recent evidence suggests mammography may not be as effective as thought. Patients with questions about having mammograms should discuss them with their doctor. Early diagnosis of breast cancer does produce better survival rates. Effective treatment for the disease varies by each patient.

A third type, colon cancer, has a long pre-cancer phase which appears as polyps. These polyps can be screened for using a test called a colonoscopy. (Some alternative tests are available, but have proven to be slightly less accurate.) Effective treatment is the removal of the polyps and it is considered to be extremely effective.

A fourth type of cancer that can be screened for is skin cancer. Some types of this disease have a long pre-cancer phase, while others have a long early cancer phase. The accurate test to screen for skin cancer is an examination by a medical doctor. Effective treatment is removing the lesion. Again, early diagnosis produces better survival rates and treatment is effective when recommendations are followed.

Other Considerations

Screening for prostate cancer in men is controversial because it is not clear if the benefits of screening outweigh the risks of follow-up diagnostic tests and cancer treatments. In 2002, the U.S. Preventive Services Task Force concluded that the evidence was insufficient to recommend for or against routine screening for prostate cancer using the prostate specific antigen (PSA) blood test or the digital rectal examination. Since there is no conclusive evidence that these tests are accurate enough to save lives, doctors generally discuss the pros and cons with the patient and have them share in the decision-making process regarding the screening. That being said, PSA testing in the United States is widespread in men 50 and older with an estimated 20 million tests being done annually.

Two types of cancer that we have failed at screening for are lung cancer and ovarian cancer. Lung cancer only sometimes has a long early cancer phase and there is no good test to detect this phase. Effective treatment is surgery, but by the time it is found using current technology, the outcome for the patient is no different than waiting until the patient has symptoms. Ovarian cancer does not appear to reliably have a long enough early cancer phase and no accurate screening test has been found. As with lung cancer, the outcome for the patient is no different than if it’s discovered once symptoms appear.

“The bad news is that many fairly common cancers such as leukemia, lymphoma, pancreatic cancer, and myeloma show little potential to be ‘screenable’ in the near future,” said Dr. Nemec. “The good news, with the exception of lung cancer, which is usually preventable by not smoking, the cancers we can screen for are the ones that cause the most deaths and disabilities.” That is why Dr. Nemec reminds patients that along with a healthy lifestyle, regular cancer screenings listed above are a person’s best protection against cancer.