Cancer in the community. Part 1: Cancer screening

Professionals working in primary care play a vital role in supporting people living with and beyond cancer. This article, the first in a four-part series, will help to update your knowledge of cancer and aims to enable you to support patients at all stages of the cancer journey. The focus of this first article is the NHS cancer screening programme.

Cancer is a common disease: if you were born after 1960 the life-time risk of being diagnosed with cancer is 1:2.¹ Macmillan Cancer Support has calculated that more than 170,000 people in the UK have been living with a cancer diagnosis for more than 30 years.¹ Cancer survival rates are much improved, thanks to better treatments, research which has led to new understanding of the disease, enhanced diagnostic equipment, screening and early detection.¹ Screening programmes detect changes in cells at a pre-cancerous stage, enabling preventative treatment and regular, more frequent monitoring of high risk patients.

WHAT IS CANCER?

Understanding cancer and how it develops will increase your confidence in answering questions from patients about cancer, and will help you understand the principles of the NHS screening programme.

There are myths and misunderstandings about cancer, which affect the way patients and families perceive and experience the diagnosis. Although there are over 200 types of cancer, the four most common types of cancer in the UK are lung, breast, prostate and bowel. 50% of cancer-related deaths in the UK are caused by these four cancers.²

Cancer is a term given to describe a disease in which previously healthy cells no longer adhere to ‘normal’ cellular behaviour and grow uncontrollably.³ Normal cells have the following key characteristics:

• They reproduce themselves only when and where they are needed
• They remain in their designated organ or role in the body
• They self-destruct if they are damaged or too old
• They mature and become specialised.

In contrast, cancer cells lose these abilities. The changes follow exposure to carcinogenic agents that damage the cells’ genes. The damage to the cells’ DNA results in cancer cells continuously dividing without maturing, and ignoring signals from other cells that would stop them growing and invading beyond their organ of origin. Cancer cells can lose the molecules on their surface that would keep them in their right place in the body, so they can detach and spread (via the bloodstream and lymphatic system). Cancer cells look abnormal under the microscope and do not function as a normal cell.³

RISK FACTORS

Cancer is caused by a variety of factors. Some cancers, including some breast cancers, have an increased risk of genetic inheritance. A recent report suggested that long-term hormone replacement therapy increases the risk of developing breast cancer three-fold.⁴

Overall, 50% of cancers are considered ‘preventable’.² Healthy lifestyle choices significantly decrease the risk of damage to the DNA. Smoking is thought to cause 20% of cancer deaths in the UK and is not only associated with lung cancer but also head and neck cancers, bowel cancer and cervical cancer. Other lifestyle factors that increase the risk of cancer include obesity, poor diet, alcohol, and lack of exercise. Environmental causes of cancer include UV light, asbestos, chemicals and radiation. Increasing age is a risk factor and infections (such as Human Papilloma Virus and Helicobacter pylori) are also known to cause cancer.

SCREENING FOR CANCER

Screening for cancer aims to detect changes in cells which indicate that cancer may develop or be developing, before signs and symptoms of the disease are obvious. If cancer is detected in its early stages, survival outcomes are improved and treatments are less extensive. Early identification of pre-cancerous change enables treatments, such as surgery, to be undertaken to remove the abnormal tissue.

The National Screening Committee (UKNSC) defines screening as:

‘a process of identifying apparently healthy people who may be at increased risk of a disease or condition. They can then be offered information, further tests and appropriate treatment to reduce their risk and⁄or any complications arising from the disease or condition’.⁵

The UK’s cancer screening programme is based on principles established by the World Health Organization in 1968 but which remain pertinent today.⁶ (Box 1)

An effective screening test needs to have some key characteristics. (Box 2)

Sensitivity: A test aims to be highly sensitive – i.e. it should ensure that a minimum number of cases of actual disease ‘slip through the net’ and remain undetected.

Specificity: The test also has to be highly specific to ensure that as few people as possible receive a ‘false positive’ diagnosis and are then subjected to further potentially unnecessary diagnostic tests and treatment.

Acceptability: The test has to be acceptable to the population it is aimed at. Highly complex, unpleasant or painful tests will not be effective as a screening programme, because the likely uptake will be very low.

Although screening can identify the presence of a developing cancer, a ‘negative’ (all clear) result cannot guarantee that the disease is not present or that it will not develop before the next screening test. All screening programmes produce ‘false positive’ results, where people are wrongly informed that they might have the condition, which leads to unnecessary investigations, treatment and anxiety. The aim is to keep the number of false positives to a minimum.

Screening programmes also produce ‘false negative’ results (where results are wrongly reported as ‘clear’), which can give false reassurance both to the person and the healthcare team. The UK National Screening Committee now talks about screening in terms of ‘risk reduction’ – rather than ‘prevention’ – to emphasise this point.⁵

The current UK screening programme is summarised in Table 1.

LIMITATIONS OF SCREENING

Screening is costly. For example, in England the cost of the breast cancer screening programme is estimated to be approximately £96 million per year; cervical screening (including the cost of treating cervical abnormalities) is estimated to cost £157 million a year.⁵

Screening also has an important ethical element that has to be considered. Screening is aimed at apparently healthy people, and might result in a stressful or worrying outcome. In addition, screening can result in people undergoing what turn out to be unnecessary investigations or treatments to prevent an illness that they might never have developed in their lifetime.

These limitations are illustrated by the controversy regarding the breast cancer screening programme. This was criticised in 2013-14 for minimising the risk of over-treatment in its information, and for creating psychological distress. The information leaflet has now been changed and improved. A 2013 Cochrane review,6 summarised the risks and effectiveness of the UK breast screening programme as follows:

‘If we assume that screening reduces breast cancer mortality by 15% and that over-diagnosis and over-treatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. More than 200 women will experience psychological distress including anxiety and uncertainty for years because of false positive findings.’

CHANGES TO CURRENT SCREENING PROGRAMMES

Cervical cancer screening

Changes to cervical screening programme are being planned. The Department of Health has indicated that screening samples will first be tested for the Human Papilloma Virus (HPV).⁷ The proposed change will make the screening more accurate, by reducing the number of false positive and false negative results. Cancer Research UK have reported that the new testing process could prevent approximately 600 cancers per year because it will identify the cancer-causing HPV infection before any abnormalities have developed in the cells.⁷

Bowel cancer screening

Proposed changes have also been announced to the bowel cancer screening programme following a successful pilot study involving 40,000 people.⁸ Public Health England has stated that the Faecal Immunochemical Test (FIT) will be rolled out across the country and will replace the Faecal Occult Blood (FOB) test currently in use.

The FIT is also a home testing kit but is simpler to use, is more accurate, and requires only one sample instead of the three needed for the current test. The current FOB test produces an ‘unclear’ result in approximately 4% of people. Most people who then repeat the test receive a normal result.

The FIT will continue to be offered to men and women aged 60-74 every two years. It is hoped that the new, simpler test will boost the uptake of bowel screening by around 10%.

REFERENCES

1. Macmillan Cancer Support. Cancer: Then and Now Diagnosis, Treatment and After Care from 1970-2016. 2016 http://www.macmillan.org.uk/documents/campaigns/cancer-then-now-report-final-online.pdf

2. Cancer Research UK. Cancer Incidence Statistics http://www.cancerresearchuk.org/health-professional/cancer-statistics/incidence#heading-One

3. Almeida CA, Barry SA. Cancer: Basic Science and Clinical Aspects. Massachusetts., USA. Wiley-Blackwell, 2010

4. Jones M E, Schoemaker M J, Wright L, et al. Menopausal hormone therapy and breast cancer: what is the true size of the increased risk? British Journal of Cancer 2016; 115: 607–615. doi:10.1038/bjc.2016.231 www.bjcancer.com Published online 28 July 2016 http://www.nature.com/bjc/journal/v115/n5/full/bjc2016231a.html

5. NHS Cancer Screening Programmes 2011a NHS Cancer Screening Programmes 2011b

6. Gøtzsche PC, Jørgensen K Cochrane review on breast cancer screening 2013 http://www.cochrane.org/CD001877/BREASTCA_screening-for-breast-cancer-with-mammography

7. Department of Health: Changes to cervical cancer screening News announcement July 2016 https://www.gov.uk/government/news/changes-to-cervical-cancer-screening

8. Department of Health UK national Screening Committee recommends new bowel cancer screening test https://www.gov.uk/government/news/uk-nsc-recommendations-include-new-bowel-cancer-screening-test