Introduction

In 1968, the World Health Organization (WHO) published guide­lines on the principles and practice of screening for disease, which are often referred to as the ‘Wilson and Jungner criteria' (1).

To quote Wilson and Jungner, ‘the central idea of early disease detection and treatment is essentially simple. However, the path to its successful achievement (on the one hand, bringing to treatment those with previously undetected disease, and, on the other, avoiding harm to those persons not in need of treatment) is far from simple, though sometimes it may appear to be deceptively easy'. With the onset of genetic screening, new controversies around screening emerged and in 2008, Andermann et al. (2) synthesized and modi­fied the Wilson criteria (Box 61.2).

Screening is a systematic attempt to select those who are at high risk of a specific disease from among apparently healthy individuals (3). The ultimate aim of screening is prevention of disease or to de­tect disease at an early, curable stage. There are many controversies about screening for cancer, such as the use of prostatic-specific an­tigen screening for prostate cancer, mammography screening for breast cancer, and debates around current screening for colorectal, lung, and cervical cancers (4).

Various types of screening are described which include the following:

1. Organized mass (population-b ased) screening: this involves screening of a whole population or a subgroup. It is offered to all, irrespective of the risk status of the individual, with everyone taking part offered the same services, information, and sup­port. The inputs are quality assured and the outcomes are con­tinuously monitored and evaluated (typical of cervical cancer screening programmes in Nordic countries, Netherlands, and the United Kingdom).

2.

3. High-risk or selective screening among specific populations (e.g. young women with ovarian cancer for BRCA1 and BRCA2 gene mutations).

4. Multiphasic screening involves routine use of multiple tests on the same occasion in population screening programmes for the purpose of detecting a disease in preventable or curable stages (e.g. co-testing with cytology and human papillomavirus (HPV) testing for cervical cancer).

Controversies exist with regard to the level of evidence required before screening for a disease is initiated. Even if there is a high level of evidence for efficacy and effectiveness, how the programme should be implemented needs careful consideration, particularly a clear understanding of benefits versus harms, potential or actual. In some countries, mass population screening programmes are implemented and in others, screening is dependent on access to health insurance (5). Screening organized by a healthcare system, as occurs in the United Kingdom, includes personal invitations to screening for eligible individuals and a structured organization for invitation, intervention, and management of screen detected dis­ease, clinical surveillance, and quality assurance—generally known as population-b ased screening programmes (4). Opportunistic screening usually only refers to a specifically identified group (i.e. people visiting their general practitioners or local pharmacies) and in general is less effective than population-based programmes which are able to achieve a much wider coverage of the target population.

Screening is controversial largely because benefits versus harms are not always clearly defined, there are often vested interests (e.g. fee for service) making screening a business, and the public may be left confused and at the mercy of often untested and biased information (6).