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More patients are asking for screening for cancers as public knowledge about cancers increases. As patients become more educated, they are learning more about how to maintain their health and how to prevent disease or detect disease early. Media reports about the growing rate of cancers, such as that of the colon and rectum make the public aware that one in twenty Singaporeans could contract colorectal cancer in their lifetime, especially if they have various risk factors. The concept of screening means testing people with no symptoms. It is different from undergoing tests when there are already symptoms that may suggest cancer. The latter is not 'screening', but diagnosis of symptoms.
There may be known risk factors or pre-malignant conditions that a doctor could discover during screening, or there may be no risk factors at all. If it is appropriate, further investigative tests could be conducted to see whether there is the presence of cancer.
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Screening of asymptomatic patients could be at a patient's initiative or as a community effort to reduce disease burden. Some cancers are screened as part of a public health campaign, but others are not supported by public funds and patients have to seek screening on their own.
To be effective, screening methods must detect the cancer at a stage when intervention is useful. This is at the pre-malignant stage, or if a cancer is already present, at an early malignant stage so that it can be cured.
Screening tests must be safe, simple, sensitive (not missing cancer cases) and specific (correctly distinguishing normal people from those with disease.) Ideally, it must be shown by scientific studies that screening leads to greater survival benefit.
This series of articles begins with a discussion on screening for Colorectal Cancer. | 
