ABSTRACT

Department of Oncology, Division of Gynaecologic Oncology, University Hospital, Linkoping, Sweden

WHAT DOES CANCER SCREENING ACTUALLY MEAN?

Usually in medicine a patient initiates a consultation to get advice and treatment because he/she has experienced some symptoms. In a cancer screening program, however, people are invited because they belong to a certain risk group (e.g., age). With few exceptions, they are all, by definition, asymptomatic. In an ideal situation, the cancer screening test will tell if a subject has the disease or not. There is, however, no perfect test. There is an inherent inverse relationship between the ability of a test to detect disease (sensitivity) and the ability of a test to detect the absence of disease (specificity). At times, all screening tests will miss some cases with disease (i.e., false negative results), and at times, all screening tests will suggest the presence of disease where none exists (i.e., false positive results) (1). More often, though, the test merely tells something about the risk of having or contracting a disease. For those testing positive, further tests have to be done to confirm or exclude disease. Most of those testing positive will be worried without reason and will be subject to unnecessary investigations with associated possible adverse effects. In the end, the diagnosis will be confirmed in some cases and definite treatment of the cancer disease can be instituted. The majority of those individuals are the winners in the screening game. But a minority of those would never have been troubled by their cancer, and thus are loosers. They may have a slowly developing cancer and could well die of other causes before having

symptoms from their screen-detected cancer even if it remains untreated. Some of those testing negative will still have an increased risk, or have the disease, but will be falsely reassured. In some cases, the cancer would, in spite of screening, be detected in an advanced stage when curative treatment is no longer possible. ‘‘It is the small proportion who would die of their disease in the absence of screening, but who if their cancer is screen detected, go on to die of another condition later who really benefit from screening’’ (2).