Screening and early detection of cancer

[الدكتور أحمد باذيب]

Screening and early detection of cancer

Early detection of cancer greatly increases the chances for successful treatment.

There are two major components of early detection of cancer: education to promote early diagnosis and screening.

Recognizing possible warning signs of cancer and taking prompt action leads to early diagnosis. Increased awareness of possible warning signs of cancer, among physicians, nurses and other health care providers as well as among the general public, can have a great impact on the disease. Some early signs of cancer include lumps, sores that fail to heal, abnormal bleeding, persistent indigestion, and chronic hoarseness. Early diagnosis is particularly relevant for cancers of the breast, cervix, mouth, larynx, colon and rectum, and skin.

Screening refers to the use of simple tests across a healthy population in order to identify individuals who have disease, but do not yet have symptoms. Examples include breast cancer screening using mammography and cervical cancer screening using cytology screening methods, including Pap smears. Screening programmes should be undertaken only when their effectiveness has been demonstrated, when resources (personnel, equipment, etc.) are sufficient to cover nearly all of the target group, when facilities exist for confirming diagnoses and for treatment and follow-up of those with abnormal results, and when prevalence of the disease is high enough to justify the effort and costs of screening.

Based on the existing evidence, mass population screening can be advocated only for breast and cervical cancer, using mammography screening and cytology screening, in countries where resources are available for wide coverage of the population. Several ongoings studies are currently evaluating low cost approaches to screening that can be implemented and sustained in low-resource settings. For example visual inspection with acetic acid may prove to be an effective screening method for cervical cancer in the near future. More studies that evaluate low cost alternative methods to mammography screening, such as clinical breast examination, are needed.
http://www.who.int/cancer/detection/en/

[الدكتور أحمد باذيب]

Screening for various cancers

Screening is the presumptive identification of unrecognized disease or defects by means of tests, examinations, or other procedures that can be applied rapidly.

In advocating screening programmes as part of early detection of cancer, it is important for national cancer control programmes to avoid imposing the “high technology” of the developed world on countries that lack the infrastructure and resources to use the technology appropriately or to achieve adequate coverage of the population. The success of screening depends on having sufficient numbers of personnel to perform the screening tests and on the availability of facilities that can undertake subsequent diagnosis, treatment, and follow-up.

A number of factors should be taken into account when the adoption of any screening technique is being considered:

Sensitivity: the effectiveness of a test in detecting a cancer in those who have the disease;
Specificity: the extent to which a test gives negative results in those that are free of the disease;
Positive predictive value: the extent to which subjects have the disease in those that give a positive test result;
Negative predictive value: the extent to which subjects are free of the disease in those that give a negative test result;
Acceptability: the extent to which those for whom the test is designed agree to be tested.
A screening test aims to be sure that as few as possible with the disease get through undetected (high sensitivity) and as few as possible without the disease are subject to further diagnostic tests (high specificity). Given high sensitivity and specificity, the likelihood that a positive screening test will give a correct result (positive predictive value) strongly depends on the prevalence of the disease within the population. If the prevalence of the disease is very low, even the best screening test will not be an effective public health programme.

Policies on early cancer detection will differ markedly between countries. An industrialized country may conduct screening programmes for cervical and breast cancer. Such programmes are not, however, recommended in the least developed countries in which there is a low prevalence of cancer and a weak health care infrastructure. Further, only organized screening programmes are likely to be fully successful as a means of reaching a high proportion of the at-risk population. Countries that favour cancer detection remaining part of routine medical practice, or that simply encourage people to seek specific tests at regular intervals, are unlikely to realize the full potential of screening.

The success of screening programmes depends on a number of fundamental principles:

The target disease should be a common form of cancer, with high associated morbidity or mortality;
Effective treatment, capable of reducing morbidity and mortality, should be available;
Test procedures should be acceptable, safe, and relatively inexpensive.
In a national cancer control programme, screening programmes should be organized to ensure that a large proportion of the target group is screened and that those individuals in whom abnormalities are observed receive appropriate diagnosis and therapy. Agreement needs to be reached on guidelines to be applied in the national cancer control programme concerning:

The frequency of screening and ages at which screening should be performed;
Quality control systems for the screening tests;
Defined mechanisms for referral and treatment of abnormalities;
An information system that can: -send out invitations for initial screening; - recall individuals for repeat screening; - follow those with identified abnormalities; - monitor and evaluate the programme.
For a number of reasons, patients often fail to adhere to recommended cancer screening activities. While in many cases both the patients and the health care providers understand the concept of early detection, they fail to comply with recommendations. Non-compliance is a general health problem and one that should be addressed in a comprehensive manner to improve outcome and reduce the waste of resources.

Screening that concentrates solely on a high-risk group is rarely justified, as identified risk groups usually represent only a small proportion of the cancer burden in a country. In planning the coverage of screening programmes, however, steps must be taken to ensure that all those at high risk are included. This requirement may be difficulty to fulfil. In screening for cancer of the cervix, for example, those at high risk are often difficult to recruit into screening.

[الدكتور أحمد باذيب]

Breast cancer is the most common cancer among women worldwide, and there are several possible methods for screening.

If facilities are available, screening by mammography alone, with or without physical examination of the breasts, plus follow-up of individuals with positive or suspicious findings, will reduce mortality from breast cancer by up to one-third among women aged 50–69 years (IARC, In press).

Much of the benefit is obtained by screening once every 2–3 years. There is limited evidence for its effectiveness for women 40–49 years of age (IARC, In press)(see Figure 5.2). The Health Insurance Plan (HIP) study, which used physical examinations by surgeons, suggested benefits in younger women only after they had reached their fifties (Shapiro, 1997). A cohort study in Finland suggested breast self-examination to be of benefit at all ages (Gastrin et al., 1994), as did a case-control study in Canada (Harvey et al., 1997).

However, observational studies of these latter types cannot exclude selection bias and may overestimate benefit. A randomized trial of breast self-examination in China has not found any evidence of reduction in breast cancer mortality after long-term follow-up (IARC, In press). This suggests that a programme to encourage breast self-examination alone would not reduce mortality from breast cancer. Women should, however, be encouraged to seek medical advice immediately if they detect any change in a breast that suggests breast cancer.

Unfortunately, mammography is an expensive test that requires great care and expertise both to perform and in the interpretation of results. It is therefore currently not a viable option for many countries. Although there is inadequate evidence that physical examination of the breasts as a single screening modality reduces mortality from breast cancer (IARC, In press), there are indications that good clinical breast examinations by specially trained health workers could have an important role. These come from the HIP study where mammography detected a low proportion of breast cancers, especially in women under the age of 50 (Shapiro, 1997), yet breast cancer mortality was reduced. Similarly, in the Canadian National Breast Screening Study, where the addition of mammography to such examinations in women aged 50–59 did not result in a reduction in breast cancer mortality (Miller et al., 2000a).

Given the present level of evidence, the national cancer control programme should not recommend screening by breast self-examination and physical examinations of the breast. Rather, the programme should encourage early diagnosis of breast cancer, especially for women aged 40-69 years who are attending primary health care centres or hospitals for other reasons, by offering clinical breast examinations to those concerned about their breasts and promoting awareness in the community. If mammography is available, the top priority is to use it for diagnosis, especially for women who have detected an abnormality by self-examination. It should be borne in mind, however, that cancer may be present even if the mammogram is negative. Mammography should not be introduced for screening unless the resources are available to ensure effective and reliable screening of at least 70% of the target age group, that is, women over the age of 50 years.

In determining the relative priorities for different screening programmes, it is important to recognize that breast cancer screening is intrinsically less effective than cytological screening for cervical cancer. As a rough guide, screening will produce an equivalent reduction in numbers of deaths in the two conditions only if, in the absence of screening, breast cancer mortality is three times that of cervical cancer in the age groups concerned.