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Chapter 2: Cancer: Reducing amenable mortality

Introduction

Better Cancer Care was published by the Scottish Government in October 2008. It sets out opportunities for reducing Scotland's cancer burden. In addition, BCC highlights advances in the early detection of cancer through screening and improved diagnosis and treatment. It also described a series of actions to support people living with and beyond cancer.

In this chapter, I consider the prospects for reducing mortality from the four main types of cancer in Scotland: lung cancer, colorectal cancer, female breast cancer, and prostate cancer. Discounting non-melanoma skin cancers, which usually have an excellent prognosis (over 8,000 new cases annually with 72 deaths in 2007) these four cancers comprise 54% of all newly diagnosed cancers and almost 50% of all deaths from cancer). ¹¹ The numbers of newly diagnosed cases of lung, colorectal, female breast, and prostate cancers during 2005, and the numbers of deaths during 2007 are shown in Table 1, alongside projected average annual numbers of cases and deaths for the periods 2016-2020 and 2015-2019, respectively. In the past, mortality rates from cancer in Scotland have been high compared to many other countries.

Lung cancer

Some 4,500 people in Scotland develop lung cancer each year. An estimated 90% of these lung cancers are caused by smoking. The delay between first exposure to tobacco and development of lung cancer is usually measured in decades; as a result, current patterns of lung cancer are driven mainly by historic trends in the prevalence of smoking. The prognosis of lung cancer is usually poor (the average survival from diagnosis is less than 6 months); therefore, trends in age-standardised mortality rates provide a reasonable approximation to the population's risk of developing the disease. Mortality rates from lung cancer in men increased to a peak in the late 1970s particularly among those born around the beginning of the 20th century, who took up smoking in large numbers during and after the First World War (Figure 1).

Demonstration of the harmful effects of smoking in the early 1950s led to decreases in smoking rates and subsequent decreases in lung cancer mortality rates in men from around 1980 onwards. Women tended to take up smoking in large numbers about 20 years after men, and although the rate of smoking has generally been lower in women, decreases in smoking rates were slower to materialise. Consequently, although mortality rates from lung cancer have always been lower in women than men, rates continued to increase over time and only showed signs of reaching a plateau during the mid-late 1990s (Figure 2).

Although the ideal is never to start smoking in the first place, a recent comprehensive review of evidence by the International Agency for Research on Cancer has highlighted the substantial reduction in risk that can be achieved by stopping smoking. ¹² For example, smokers who succeed in quitting by the age of 30 years eventually reduce their risk of lung cancer by around 90% compared to a continuing smoker, and the benefits begin to emerge within 5 to 9 years of quitting. This scientific evidence supports the Scottish Government's current emphasis on helping people to quit their smoking habit.

Table 1: Lung, Colorectal, Female breast, and Prostate cancer: numbers of newly diagnosed cases during 2005; average annual projected numbers of cases during 2016-2020; numbers of deaths during 2007; average annual projected numbers of deaths during 2015-2019.

* Projected average annual numbers, assuming current trends remain unchanged

As rates of smoking continue to decrease, the relative importance of other risk factors will increase, reinforcing the need to minimise exposure to other carcinogens (cancer producing substances) in industrial and environmental settings. A recent review of evidence by the World Cancer Research Fund has also suggested that a diet rich in fruit probably reduces the risk of lung cancer. ¹³

Although primary prevention offers the greatest hope for reducing the impact of lung cancer in the medium to long term, it is important to strive to improve survival, and improve symptom control and quality of life among the many people still diagnosed with the disease. While a very small proportion of patients can be cured by radical radiotherapy, cure is most likely to be achieved by surgical removal of small tumours that have not grown and spread within the lung or elsewhere in the body.

Unfortunately, the majority of patients present with tumours that are too advanced for surgery (or they may be unfit for surgery due to other adverse effects of smoking on their general health). This unsatisfactory situation has prompted an interest in early detection by screening. Despite a series of negative clinical trials of screening for lung cancer in the 1970s, interest has been rekindled in this field with the emergence of spiral computerised tomography ( CT) scanning and, with rapid developments in the field of molecular biology, the possibility that suitable biomarkers of lung cancer may be identified and screening tests developed. However, before any screening programme for lung cancer can be adopted, it will be essential to demonstrate, in the context of a well-conducted randomised controlled trial, that the benefits (in terms of reducing mortality) outweigh the risks (which include needless investigation of, and even surgical resection of, benign lesions).

For patients presenting with disease that cannot be cured, chemotherapy and radiotherapy can play a part in extending life and in disease palliation alongside more general palliative care interventions.

Colorectal cancer

Some 3,500 people in Scotland develop colorectal cancer each year. Trends in mortality rates of colorectal cancer for males and females are included in Figures 1 and 2, respectively. The main risk factors for colorectal cancer are high levels of consumption of red and processed meat, high levels of alcohol consumption (especially in men), and body fatness. ¹³ Protective factors include a diet rich in fibre and vegetables, and regular physical activity (which can reduce the risk of colon cancer substantially). ¹³ Since trends in these risk and protective factors over recent decades have not been favourable, the gradual reduction in colorectal cancer mortality rates reflects improved survival. This improvement is mainly due to advances in preparation of patients before surgery, surgical techniques (particularly for rectal cancer), anaesthetic techniques and post operative care. The introduction of adjuvant chemotherapy for patients with more advanced disease has also had an impact. Radiotherapy (especially pre-operatively) can improve local control of disease in some patients with rectal cancer. While clinical audit shows that many of the standards for colorectal cancer care are being achieved in Scotland, the prospect of cure is highest for patients with localised disease, making early detection a priority.

Randomised controlled trials carried out in USA, Denmark, and Nottingham have shown that annual or biennial screening with a faecal occult blood test ( FOBT) can reduce mortality from colorectal cancer. A subsequent pilot study based in Fife, Grampian, and Tayside NHS Boards established that a national screening programme for colorectal cancer was feasible. From May 2007 a national screening programme began with the first invitations to 50-74 year olds in Tayside, Grampian and Fife to participate in the new screening programme. Other NHS Boards will follow with the last rollout planned for 2009. Once bowel screening is established, mortality from bowel cancer should decrease by around 16%, preventing approximately 150 premature deaths per year.

Research in Scotland has also increased understanding of the genetic basis of colorectal cancer and in future may lead to improvements in identifying those most at risk of developing colorectal cancer and hence enable better targeting of prevention, screening, and treatment. ¹⁴

Figure 1: Annual age-standardised mortality rates from lung, colorectal and prostate cancers, males, Scotland, 1968-2007

Source: GRO(S)

Figure 2: Annual age-standardised mortality rates from lung, breast and colorectal cancers, females, Scotland, 1968-2007

Source: GRO(S)

Female breast cancer

Some 4,000 women in Scotland develop breast cancer each year. Risk factors for breast cancer include genetic susceptibility, and reproductive factors that are not readily amenable to change, such as early onset of menstruation, nulliparity (having had no births), older age at birth of first child, and late menopause. Potentially more modifiable factors include alcohol intake, body fatness (a risk factor for post-menopausal breast cancer), use of hormone replacement therapy, and use of oral contraceptives. Protective factors include breast feeding, and probably physical activity, the latter being especially relevant to post-menopausal breast cancer.

The trend in mortality rates from female breast cancer is shown in Figure 2. The increase in breast cancer mortality until 1989 is consistent with increases in incidence most likely driven by changes in reproductive factors. The more recent decrease in mortality is due to better survival, reflecting improvements in therapy, including better quality surgery and radiotherapy, and the use of systemic adjuvant therapy. The Scottish Breast Screening Programme also contributes to the reduction in mortality from breast cancer. ¹⁵

'The more recent decrease in mortality is due to better survival, reflecting improvements in therapy, including better quality surgery and radiotherapy, and the use of systemic adjuvant therapy. The Scottish Breast Screening Programme also contributes to the reduction in mortality from breast cancer.'

Chemoprevention (taking drugs to prevent the development of cancer) is currently being researched in women at genetically high risk of breast cancer, but otherwise, the future prospects for primary prevention of breast cancer are limited to addressing the modifiable risk factors, such as alcohol intake and body fatness. Although the magnitude of excess risk of breast cancer due to alcohol is not very large, the high incidence of breast cancer means that alcohol is responsible for more cases of breast cancer than any other type of alcohol related cancers among women. ¹⁶Other potential avenues for reducing mortality from breast cancer include future developments and refinements in breast screening, and the rapidly increasing understanding of the molecular mechanisms of breast cancer, which is already leading to tailoring of some novel therapies. ¹⁷

Prostate cancer

Some 2,500 men in Scotland develop prostate cancer each year. Trends in mortality rates of prostate cancer are included in Figure 1. The causes of prostate cancer are poorly understood. The risk of disease increases with age, and is higher among men with a family history of prostate cancer (and possibly some other types of cancer), and among men of African descent. A recent review of evidence by the World Cancer Research Fund suggested that diets high in calcium probably increase the risk of prostate cancer, whereas risk is probably reduced by a diet containing lycopene (as found in tomatoes, for example), and selenium (as found in fish, wholegrain, and wheatgerm, for example). ¹³ Due to remaining uncertainties about the precise role of diet in the aetiology of prostate cancer, the prospects for primary prevention are limited at present.

Limited prospects for primary prevention have led to considerable interest in the possibility of screening for prostate cancer by widespread application of the prostate-specific antigen ( PSA) test. A major challenge presented by prostate cancer is that only a proportion of tumours are aggressive and life-threatening - more men die with prostate cancer than die from prostate cancer. If screening were to mainly identify slow-growing tumours with no impact on life expectancy, it would be unlikely to have a major impact on mortality from prostate cancer. However, in the Tyrol region of Austria, where treatment is freely available to all patients, and where PSA testing is widespread, there has been a reduction in prostate cancer mortality significantly greater than the reduction in the rest of Austria. ¹⁸ It is not clear whether this has occurred because of screening and early detection, or due to more effective treatment (or both). However, the balance of benefits and risks of screening for prostate cancer remains unclear, and any decision to implement an organised programme of population screening must await the results of ongoing randomised controlled trials in mainland Europe and the United States.

The variable biological behaviour of different prostate cancers poses difficulties for selecting the most appropriate treatment. The main options for cure of localised tumours are radical prostatectomy (surgical removal of the prostate), external beam radiotherapy, or brachytherapy (implantation of small radioactive "seeds" into the prostate gland). However, because potential side effects of treatment, such as incontinence and impotence, can substantially reduce quality of life, it is important to identify those men whose cancers are most likely to progress. While the microscopic features of tumours can help distinguish between those that are slow-growing and those that are aggressive, research is currently focused on identifying specific characteristics of those tumours that are most likely to progress and warrant intensive treatment. The explanation for the recent slight decrease in mortality from prostate cancer in Scotland is unclear, but seems more likely to be due to better application of established treatments than to early detection through PSA testing.

Summary

Although rates of mortality from cancer in Scotland have historically been high compared to many other countries, recent trends provide some grounds for optimism. Progress in reducing mortality may be accelerated by uniform application of existing knowledge, as well as new knowledge emerging from research. In the long term, smoking cessation is likely to deliver the greatest reductions in incidence of and mortality from cancer in Scotland, but tackling other risk factors such as alcohol consumption, poor diet, body fatness, and physical inactivity will potentially also have a substantial impact. However, the inevitable time lag between primary prevention interventions and reductions in cancer incidence, coupled with projected increases in numbers of cases simply due to ageing of the population, mean that effective screening (where appropriate), treatment, and palliative care must remain priorities for the NHS in Scotland.

'Although rates of mortality from cancer in Scotland have historically been high compared to many other countries, recent trends provide some grounds for optimism. Progress in reducing mortality may be accelerated by uniform application of existing knowledge, as well as new knowledge emerging from research.'

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