Trends in colorectal cancer mortality in Europe
A retrospective analysis
“Trends in colorectal cancer mortality in Europe: retrospective analysis of the WHO mortality database” by Driss Ait Ouakrim and colleagues (BMJ 2015;351:h4970).
Objective—To examine changes in colorectal cancer mortality in 34 European countries between 1970 and 2011.
Design—Retrospective trend analysis.
Data source—World Health Organization mortality database.
Population—Deaths from colorectal cancer between 1970 and 2011. Profound changes in screening and treatment efficiency took place after 1988; therefore, particular attention was paid to the evolution of colorectal cancer mortality in the subsequent period.
Main outcomes measures—Time trends in rates of colorectal cancer mortality, using joinpoint regression analysis. Rates were age adjusted using the standard European population.
Results—From 1989 to 2011, colorectal cancer mortality increased by a median of 6.0% for men and decreased by a median of 14.7% for women in the 34 European countries. Colorectal cancer mortality dropped by more than 25% in men and 30% in women in Austria, Switzerland, Germany, the United Kingdom, Belgium, the Czech Republic, Luxembourg, and Ireland. By contrast, mortality fell by less than 17% in the Netherlands and Sweden for both sexes. Over the same period, smaller or no declines occurred in most central European countries. Substantial increases in mortality occurred in Croatia, the former Yugoslav republic of Macedonia, and Romania for both sexes and in most eastern European countries for men. In countries with decreasing mortality, reductions were more important for women of all ages and men younger than 65 years. In the 27 European Union member states, colorectal cancer mortality fell by 13.0% in men and 27.0% in women, compared with corresponding reductions of 39.8% and 38.8% in the United States.
Conclusion—Over the past 40 years, there has been considerable disparity in the level of colorectal cancer mortality between European countries, as well as between men and women and different age groups. Countries with the largest reductions in colorectal cancer mortality are characterised by better accessibility to screening services, especially endoscopic screening, and specialised care.
Why do the study?
Colorectal cancer, also known as bowel cancer, accounts for about 10% of all new cancers worldwide. It is the third most common cancer worldwide and the fourth most common cause of death. In Europe, it is the second most common cause of death from cancer (lung cancer is the most common).
The cancer typically begins as small polyps in the large intestine (80%) or rectum (20%). When it metastasises to the lymph nodes, five year survival is 53-89%, depending on the number of nodes affected. When distant organ metastasis is present—typically the liver—five year survival is only 11%.
What has been done to reduce the number of deaths? Screening has helped. Faecal occult blood testing, flexible sigmoidoscopy, and colonoscopy are all screening tests used in many Western countries, including the United Kingdom, United States, Denmark, Sweden, and other countries where colorectal cancer has a high incidence, including China. Earlier detection of adenomatous polyps—the most common precursor for colorectal cancer—has led to endoscopic removal and a decline in colorectal cancer mortality rates in many countries.
But not all countries have achieved such change. Data suggest that northwest Europe has seen the largest decline in colorectal cancer mortality compared with the rest of Europe. Therefore, the authors decided to investigate this further and analyse long term trends from all European countries and provide up to date epidemiological data on colorectal cancer mortality.
What did the authors do?
The number of deaths from colorectal cancer was obtained from the World Health Organization mortality database, a compilation of mortality data by age, sex, and cause of death, as reported annually by WHO member states from their civil registration systems. Data were obtained for 34 European countries and the United States between 1970 and 2011.
The authors searched for cause of death by referring to three versions of the international classification of diseases (International Classification of Diseases 8th-10th revisions) used over this period. ICD codes included cancers of the colon, rectum, anus or anal canal or both, and relevant variations.
Missing data and over-reporting
Although the authors were able to collect data for most or all of the time period being analysed, there were exceptions. Cyprus was not included because data were available for four years only. For almost all central and eastern European countries, data were available from early to mid-1980s until 2009-10.
For Switzerland, data were available only until 2010. Furthermore, a change in coding practice in 1994 resulted in an over-reporting of cancer mortality before 1994. Therefore, the authors applied a correction factor of 0.94 to all mortality rates before 1995. This was thought to be due to a true downward shift in cancer mortality for some cancers and a simultaneous change in ICD-10 classification in 1995 (ICD-8 to ICD-10), and a re-analysis of data verified a likely coding process error.
The authors used the direct method of age specific population estimates from the WHO mortality database to work out age adjusted distribution of the standard European population. Direct versus indirect standardisation is an important epidemiological concept and common exam topic (see box 1).
In this study, joinpoint regression was performed over the whole period to identify years when significant changes in mortality rates occurred. Joinpoint regression analysis is a statistical technique that describes changing trends over successive segments of time, and the amount of increase or decrease within each segment. A line of best fit is then applied to statistical changes in trend. Joinpoint analyses are performed for incidence and mortality trends. Annual percentage changes were then calculated for each country. Analyses were conducted separately for men and women of all ages, and for age specific categories (<65, 65-79, ≥80 years).
Direct v indirect standardisation
In direct standardisation, we take the observed age specific mortality rates from each population and apply them to a specified standard population with a known age structure. This calculation will generate an age adjusted summary rate.
The aim is to compare two populations by working out how many deaths there would be if each population kept its own observed age specific mortality rates but the population structure of each was the same.
In indirect standardisation, we apply a set of standard age specific death rates to the real age structure of the study population and compare the total number of expected deaths with the observed number of deaths. This calculation will generate a standardised mortality ratio.
Box 1: Information needed to calculate
- Age specific mortality rates for all the populations under study
- Appropriate standard population with known age distribution
- Age specific mortality rates for a standard population
- Age structure of study populations
- Total number of deaths in study populations
What did they find?
Large differences in colorectal cancer mortality were seen between men and women and between countries, including those with similar high level economies.
In the 27 European Union member states, colorectal cancer mortality fell by 13.0% in men and 27.0% in women, compared with corresponding reductions of 39.8% and 38.8% in the United States.
The authors observed increasing mortality rates of colorectal cancer mostly in countries in southern, central, and eastern Europe, with the exception of the Czech Republic (see figure).
This time period was of particular interest because profound changes in screening and treatment efficacy took place in 1988. During this period colorectal cancer mortality increased by a median of 6.0% for men and decreased by a median of 14.7% for women in the 34 European countries studied. Reductions in colorectal cancer mortality of more than 25% in men and 30% in women occurred in Austria, Switzerland, Germany, the UK, Belgium, the Czech Republic, Luxembourg, and Ireland. By contrast, mortality rates fell by less than 17% in the Netherlands and Sweden for both sexes.
For all of Europe combined, the reductions in colorectal cancer mortality were more marked for men under age 65 years, whereas reductions for women younger than 80 years were similar.
Strengths and limitations
The use of routinely collected data is strongly encouraged by the UK National Institute of Health Research, which has pushed for researchers to make better use of data repositories, including mortality databases such as the WHO mortality database.
Critics are right to question the comprehensiveness of data that are routinely collected, particularly if on a national or international scale. Are coding practices—that is, death registration—uniform across countries?
Considerable differences in mortality trends in colorectal cancer occur across European countries, particularly compared with the US.
Epidemiological studies such as this cannot answer the question of what factors are contributing to the trends observed. The authors speculate, however, that these are likely to be inherent age and sex differences, lifestyle choices, patient awareness, and screening uptake.
The authors noted that reductions in mortality began earlier and were larger for women than men. They hypothesise this is because men are less likely than women to access healthcare services and women may use oestrogenic hormones, which reduce their risk of colorectal cancer. Observational data strongly support the use of screening for colorectal cancer to reduce mortality in areas with high incidence. Men have been observed to engage less than women.
Geographical disparities between European countries include an increase in alcohol consumption in certain countries—namely, the former Soviet Union, which probably contributes to higher incidence and mortality levels of colorectal cancer in those countries. The so called Mediterranean diet has been associated with a moderately protective effect against colorectal cancer. Lower adherence to this dietary pattern over the past 30 years has been reported in Portugal, Spain, Italy, and Greece.
Despite a concerted effort by health authorities to engage with communities in the 2000s, screening practice varies widely across European countries. One survey found that between 4% (Netherlands) and 61% (Austria) of a country’s population had faecal occult blood test screening performed. A smaller but still considerably wide range was seen for uptake of endoscopic examination of the large bowel (25% in France) and (10% in Netherlands).
What does the study mean?
Colorectal cancer mortality is falling in most European countries, particularly in western and northern Europe, compared with southern, central, and eastern Europe. Why? We’re not sure yet, but it may be caused by individual countries’ diet, lifestyle, and engagement with their healthcare providers.
Targeting populations of countries that have high mortality with better primary and secondary prevention treatment, including screening uptake, is one solution. In countries with high mortality rates from colorectal cancer, governments should prioritise such preventable deaths as an important public health problem and raise patient awareness. 1
1Colchester General Hospital, UK
Correspondence to: firstname.lastname@example.org
Competing interests: None declared.
Provenance and peer review: Commissioned; not externally peer reviewed.
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Cite this as: Student BMJ 2015;23:h6124