In 2013, an estimated 1,660,290 people in the United States will be diagnosed with cancer, and 580,350 will die of cancer. Estimates of the premature deaths that could have been avoided through screening vary from 3% to 35%, depending on a variety of assumptions. Beyond the potential for avoiding death, screening may reduce cancer morbidity since treatment for earlier-stage cancers is often less aggressive than that for more advanced-stage cancers.
Prospective, randomized, controlled trials and meta-analyses of prospective, randomized, controlled trials.
The randomized, double-blinded, controlled trial is the gold standard of study design. To achieve this ranking, the study allocation must be blinded to the investigator both before and after the randomization and the assignment to intervention group. This design provides protection from allocation bias by the investigator and from bias in the assessment of outcomes by both the...
Several potential harms must be considered against any potential benefit of screening for cancer. Although most cancer screening tests are noninvasive or minimally invasive, some involve small risks of serious complications that may be immediate (e.g., perforation with colonoscopy) or delayed (e.g., potential carcinogenesis from radiation). Another harm is the false-positive test result, which may lead to anxiety and unnecessary invasive diagnostic procedures. These invasive diagnostic procedures carry higher risks of serious complications. A less familiar harm is overdiagnosis, i.e., the diagnosis of a condition that would not have become clinically significant had it not been detected by screening. This harm is becoming more common as screening tests become more sensitive at detecting tiny tumors. Finally, a false-negative screening test may falsely reassure an individual with subsequent clinical signs or symptoms of cancer and thereby actually delay diagnosis and effective treatment.
A 2009 publication of preliminary results of a cancer screening project in Japan using multiple whole-body screening technologies illustrates clearly the problems of false-positive screening results and potential overdiagnosis.
The project enrolled 1,217 healthy volunteers, aged 35 years and older between August 2003 and July 2004. The volunteers were employees of Hamamatsu Photonics K.K. and affiliated companies in Japan. Participants participated in a company-wide health insurance program and most received mandatory annual employee's health check-ups , including chest x-ray, fecal occult blood (FOB) testing, upper gastrointestinal series, and mammography screening for many years. Twenty applicants with a prior history of cancer were excluded, leaving 1,197 participants in the evaluation. All enrollees could be considered at low risk for screen-detected cancer.