Gettysburg Medical News
 The Clinical View
 by P.E. Hoffsten, M.D.
 29 September 2005

WHY SCREEN FOR CANCER?

            A hundred years ago, the leading cause of death in the United States was an infection.  Pneumonias were very common and then there were no antibiotics to treat them.  As tuberculosis, pneumonia and various other infections have been brought under control, heart disease has blossomed into the leading cause of death in the United States accounting for about one-fourth of all people who die.  If you were born and raised in the United States, there is one chance in four that you will die of heart disease.  A number of heart disease related deaths are very sudden and thus might be thought of as merciful with little suffering.  However, the five million people who die from heart failure each year may have a prolonged and miserable course like many of those that die from cancer.

            The second leading cause of death in the United States is cancer.  The most common fatal cancer in men and women is now cancer of the lung.  For men, cancer of the prostate and cancer of the colon are the second and third most common causes of death from cancer.  In women, cancer of the breast and cancer of the colon are the second and third leading causes of death.  The reason that cancer is such a feared disease revolves about its protracted course with a slow deterioration. People seem to hate disability and dependency on others.  Avoiding this does seem to be very worthwhile.  There is also the belief that eventually death will be associated with pain and suffering.  From some individuals, this is certainly true.

            Thus, the specific answer to the question of why do cancer screening is easily answered.  The object is to avoid dependency, disability and death from cancer.

            The second and perhaps more pertinent question is, “Does cancer screening work?”  Does it lead to more frequent cures, avoidance of dependency and disability and improved mortality figures?  The answer is “yes”; for some tumors screening for cancer does improve the quality of life and the length of life.  Balanced against this must be considerations regarding the cost of the screening test, the risk of the screening test and something called its “specificity” and its “sensitivity”.  In general, screening tests are thought of as something that is useful for an entire population as opposed to an individual.  Thus, the cost of the test has to be reasonable.  Secondly, the test has to be relatively safe.  Blood tests carry virtually no risk.  Doing a total colonoscopy does take general anesthesia and there is a significant risk.  If the test only finds 20% of the cancers that are present, it is not felt to be very “sensitive” and therefore not a useful test. Ideally, we would like tests that are 95% sensitive at finding cancers that are present.  By the same token, a test that finds lots of positive results but not many real cancers has a very high false negative result and therefore, a very low specificity.  We would like to have a cancer test that when positive means that there is really a cancer there.  For women undergoing breast biopsy, this is a rather a convoluted result.  It is really nice to have a negative breast biopsy.  It would be even nicer not to have to have the biopsy in the first place.  As it stands now, seven out of eight breast biopsies are negative and the specificity of mammography is not as good as we would like.

            With the above considerations, which tests have been clearly shown to save lives by detecting a cancer early and getting rid of it?  The list is below:

            Colon cancer patients are very definitely benefitted by early detection of their tumor.  Specifically, colon cancer maybe the only cancer that is “preventable”.  Colon cancers almost always come as benign polyps in the bowel before the cancer ever develops.  Therefore, if we do screening colonoscopy and remove any polyps before they turn into cancer, the colon cancer never comes.  Simply screening for hidden blood in the colon decreases the mortality of colon cancer by 33%.  Since not all polyps in the colon turn into cancer, there is no way to estimate with certainty what the lifesaving effect of colonoscopy is.  But it is certainly the most sensitive method and the most specific method of detecting colon cancer and preventing the same.   At the present time, recommendations are that a screening sigmoidoscopy be done every five years and then a complete colonoscopy be done every ten years for individuals over age 50.  If there is a family history of colon cancer, more frequent screening should be done.

            Breast cancer in women has clearly been shown to have a decreased mortality in those individuals whose tumor is found by mammography.  There is an approximately 35% decrease in mortality for woman undergoing surveillance mammography.  At the present time, high risk woman over age 40 are recommended to have mammography every year.  For low risk women, every two years seems to be adequate.  A family history of any blood female relative who has had a cancer of the breast puts that woman into the high risk group.

            Screening for prostate cancer is more controversial.  One of the most common blood tests asked for by men is a PSA (prostatic specific antigen blood test).  Thus far, large scale studies to see if this prevents cancer morbidity and mortality are still in process and there is no clear evidence that having this test done to detect an early cancer prevents mortality or morbidity from prostate cancer.  In my opinion, these studies will eventually show that there is benefit to early detection of a prostate cancer.  While digital rectal exam is still recommended by authorities in this field, there is no information that would suggest this test is very useful for detecting cancer of the prostate.  Specifically, digital rectal exam has  a very low sensitivity and very low specificity.

            Cancer of the lung is the leading cause of death from cancer in both men and women.  On average, cancer of the lung carries a 95% two year mortality.  Most unfortunately, there is no screening test thus far that has been shown to impact this mortality figure.  Screening chest films looking for cancer of the lung have no benefit in spite of being tested many times over many years.  The best screening test for cancer of the lung is to stop smoking and stay out of smoky environments.  If a person smokes cigarettes, there are no screening tests that will help prevent mortality from cancer of the lung.

            Cancer of the cervix was previously a major cause of cancer death in the United States.  With the invention of the Pap test that has significantly improved.  The death rate from cancer of the cervix has been decreased by 70% in the last 50 years.  Since cancer of the cervix is most commonly caused by a virus called human papilloma virus, screening for cancer of the cervix should begin in at a very early age.  Present recommendation is the first Pap test should be done three years after the age at which a woman first has intercourse.  It should be then done on a regular basis depending upon the woman’s risk category.  Women with multiple sexual partners should have annual pap tests.  For monogamous woman who have had no positive Pap tests for 10 years and are more than age 50, further pap tests are not necessary.

            Cancer of the ovary and cancer of the uterus are significant risk factors for women.  Some women chose to remain on estrogen replacement therapy over a prolonged period of time.  These women require annual uterine biopsies to ensure that there is not a developing cancer of the uterus.  For women with certain genetic characteristics, screening tests of cancer of the ovary are worthwhile.  For the general population, screening tests for cancer of the ovary do not seem to have an impact demonstrated to this time.

            Annual review of the skin surface at age 30 and after is a recommended step.  This is especially true for those “sun worshipers” that spend a great part of their young life maintaining a beautiful tan.  This beautiful tan may look good but massively increases the risk of skin cancer in later years.  Removal of skin tumors early is both cosmetically important and reduces the risk of major mortality.

            For all other cancers there are no screening tests that impact the outcome of a cancer as measured by the general population statistics.

            The healthcare providers at your local clinics are aware of the above considerations and can help in providing cost effective, safe, sensitive and specific recommendations for cancer screening.