Cancer - Screening and early detection

Early detection of cancer greatly increases the chances of successful treatment. The 2 components of early detection of cancer are early diagnosis (or downstaging) and screening. Early diagnosis focuses on detecting symptomatic patients as early as possible, while screening consists of testing healthy individuals to identify those with cancer before any symptoms appear.

Early diagnosis

Early diagnosis programmes aim to reduce the proportion of patients diagnosed at a late stage. These programmes have 2 main components:

• increased awareness of the first signs of cancer among physicians, nurses and other health care providers as well as the general public; and
• improved accessibility and affordability of diagnosis and treatment services, and improved referral from first to secondary and tertiary levels of care.

Early diagnosis is relevant to all cancers. Early diagnosis programmes need to be in place and subject to continual improvement, even when efficient screening programmes have been established.

Screening

Screening refers to the use of simple tests across a healthy population to identify individuals who have a disease but do not yet have symptoms. Examples include breast cancer screening using mammography or clinical breast exams, and cervical cancer screening using pap smears or human papillomavirus tests.

Screening programmes should be undertaken only when their effectiveness has been demonstrated, when resources (personnel, equipment, etc.) are sufficient to cover nearly all the target group, when facilities exist to confirm diagnoses and to treat and follow up with those screened positive, and when the prevalence of the disease is high enough to justify the effort and costs of screening.

Even when implemented properly, screening programmes are associated with some undesirable effects, which include:

• Falsely positive screening tests that result in additional testing, invasive diagnostic procedures and patient anxiety.
• Falsely negative screening tests that provide false reassurance and can result in delayed presentation and diagnosis when symptoms appear.
• Overdiagnosis of asymptomatic and indolent cancers that would have never caused symptoms nor posed a serious health threat. Overdiagnosis results in unnecessary treatment that injures the patient (for example, overdiagnosis is frequent with prostate-specific antigen (PSA) screening for prostate cancer).
• Overtreatment of benign findings or of precancerous lesions (for example, hysterectomy to treat precancerous lesions of the cervix).

The importance of these harms varies according to the screening tests, the population groups targeted for screening and the quality of the screening programmes.

Weighing the harms against the benefits of screening has led WHO not to recommend mammography screening in women younger than 50 years of age. Based on the existing evidence, mass population screening can be advocated only for cervical, breast and colorectal cancer. Lung cancer screening has been piloted in some EU countries, with evidence showing that it can reduce mortality, but only in heavy smokers (i.e. people who have smoked more than 20 pack-years); screening does not reduce mortality in light or non-smokers.

In many countries in the WHO European Region, private or even public entities offer screening that is not evidence based, such as thyroid or gynaecological cancer screening with ultrasound or lung cancer screening with X-ray or a full body scan. WHO recommends against such practices as they do not bring any benefit and can cause harm to patients, such as anxiety and invasive follow-up procedures.

Systematic prostate cancer screening of all men above a certain age using PSA is not recommended by WHO.

Distinguishing cancer screening from early diagnosis

Early diagnosis requires ensuring rapid patient presentation, diagnosis and treatment as soon as first symptoms appear. It is relevant to all types of cancer.

Screening is relevant to only a subset of cancers. Cervical cancer screening is the most cost-efficient; it enables cure at a precancerous stage of the disease with minor surgical treatments. This is not the case for breast, prostate or lung cancer. Some colorectal cancer can also be identified at a precancerous stage through screening.

Barriers to early cancer diagnosis and treatment

Early diagnosis programmes focus on reducing delays between the detection of first symptoms and treatment by ensuring that:

• people are sensitized enough to consult health professionals as soon as symptoms appear, without being delayed by any financial, logistic or psychosocial barriers;
• the health staff consulted react appropriately and rapidly, thanks to adequate training and clear referral guidelines; and
• diagnostic and treatment services are accessible rapidly and deliver optimal quality at an affordable cost.

At all stages, barriers can reduce patients' chances of being diagnosed and treated quickly. Barriers may include poor cancer awareness among the public; suboptimal knowledge at the primary health care level about cancer symptoms and/or adequate diagnosis follow-up; poor accessibility; low affordability and/or quality of diagnosis and treatment services (waiting lists, errors in diagnosis, administrative red tape, unclear referral pathways, etc.); and the many logistic, financial and psychosocial barriers preventing patients from accessing services rapidly.

A major objective of early diagnosis programmes is to reduce these barriers. This is also a prerequisite for implementing screening programmes, because to be successful screening programmes require rapid, adequate-quality diagnosis follow-up and treatment for people screened positive. Ensuring early diagnosis is a prerequisite to launching a screening programme and needs to be maintained once screening reaches high coverage.

Early diagnosis programmes are comparatively easy and inexpensive to implement. Because they cover symptomatic patients only, their resource usage is much lower than screening programmes, which target entire populations.