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Epidemiology studies the presence of illnesses in the population, evaluating possible causes amongst contingent conditions and risk factors; it is a key tool for the promotion of preventive action.
After cardiovascular diseases, cancer holds the second place for being one of Italy's most severe causes of death. In 1970 there have been 91.000 deaths for cancer: 52.000 men and 39.000 women. Over the years, the number increased significantly, and in the year 2000, it is estimated that 138.000 people died of cancer, of which 83.000 men and 55.000 women.
Epidemiology's main objectives in the field of cancer are the study and prediction of the illness. This is done by assessing its frequency in the population, and by researching how the possibility of becoming ill varies in relation with various risk factors.
Variations in the cancer incidence rate between different population groups, for instance, suggest to the epidemiologist the importance of critical environmental, occupational, social factors, or specific lifestyles as causes of specific cancers. This motivates investigations on the relation between risk factors and the disease together with the promotion of actions which would be useful to fight those causes.
Epidemiology uses several indicators, the most important being incidence, survival, prevalence, and mortality. By considering those indicators as aspects of a whole phenomenon, it is possible to describe the spread of oncological diseases in the population. (see Table 1)
Incidence
Incidence is the number of new cancer cases in a given population
over a given period of time (usually a year).
It can be presented as incidence rate (raw) explaining the number
of new cases in the year, in a given population (usually 100.000 people)
or as standardised incidence rate. This artificial measure, can be
useful to compare the risk among different populations. It takes into
account the different per age-structure of all compared populations
thus avoiding, for instance, that populations with a higher number
of elderly people can be considered at major risk. The high frequency
of diseases amongst the elderly, higher than that amongst young persons,
determines a larger number of cases. Incidence is an important risk
factor in a population. In Italy, during the last 30 years, the number
of cancer cases has grown, from 149 thousand of new cases in 1970,
to 234 thousand in 2000 –136 thousand women and 98 thousand
men-. The data analysis shows that the cause of the big increase is
more connected to the fact that the population gets old than to the
increase of the risk of becoming ill in the past years. In fact the
standardised taxes are on reduction during the last decade, at least
for thus that concerns men. By analysing the oncological risk by birth,
we can observe that the probability of becoming ill progressively
increased in the next birth cohort in the past Century, (i.e. births
in post-war period) The data suggest that later generations present
a smaller risk. These elements seem to indicate that the risk trend
is linked to the industrialisation process of the ‘900, which
caused the progressive evacuation of the countries, the consequent
urbanisation progress, and the change of rhythms, lifestyles and work
that involved millions of Italians. For example, if we consider the
phenomenon by different geographic areas of our Country, the reduction
of cancer risk among those born after the 1950’s is not homogeneous,
though it is more evident in the North than in the South, bearing
in mind that the historical differences between the more disadvantaged
North and the South may well reduce in the future
Survival and Prevalence
Cancer survival in percentage indicates the number of survivors to cancer out of one hundred patients. 5-year-survival indicates the number of survivors after five years from the date of the beginning of the illness. 5-year cancer survival has increased from 33% for diagnosis of the 1970's to 39% for diagnosis of the 80's. It is estimated that survival will improve with more recent diagnosis, so prognosis will get better in future years.
Cancer prevalence is the number of survivors to a past or recent cancer diagnosis amongst people from a population of a given geographical-area. If it relates to a population (prevalence proportion), prevalence indicates the proportion of survivors from that population, who, in a given moment, have, or have had, experience of cancer (the calculation is usually made over a population of 100.000 citizens).
Prevalence is valued as a useful measurement to estimate a population's oncological burden. In its various subdivisions, it can be used to estimate the number of cancer patients who would be needing a medical check-up, or that of those in need of an active clinical follow-up due to high risk of recurrences.
In Italy, the population ageing process, the consequent increase of cancer cases, especially amongst the elderly, and a better survival, are all causes for an increase in prevalence over the past decades. Prevalent cases in 1970 were 820,000, and it is estimated that they became 1.3 million in the year 2000. This number means a high increase of the health demand and makes surveillance plans and control plans necessary.
Results of the EUROPREVAL European study show that in Sweden, Switzerland, Germany and Italy (analytical data for Italy are provided by ITAPREVAL) the highest levels of prevalence are recorded for most cancer sites, whereas Estonia and Poland have the lowest levels. Poland, especially, shows 1170 cases out of 100.000 people, in contrast with 3050 Swedish cases out of 100.000 people. Prevalence results from a complex phenomenon: it is associated with high incidence and high survival in Sweden, where the values are high, and in Poland it is associated with lower cancer incidence levels compared to other European Countries, and low survival to the disease. Breast cancer (34% of female cancers in Europe), and Colo-rectal cancer (15% of male cancers in Europe) are the diseases with highest prevalence. Most prevalent cases refer to elderly: 57% is represented by over 65.
Mortality
Cancer mortality in the year 2000 in Italy causes 30% of total deaths. In the last thirty years the number of deaths in each year progressively increased, but in the last decade the increase was less obvious than before.
Once we exclude the effect of the different age structures in the populations (e.g. less cancer cases in the 70's as the population was younger), it is observed that the standardized mortality rate for 100.000 people has not changed in the last century's decade. 230 men died both in 1990 and in the year 2000, whereas 140 women died in 1990 and 130 in 2000.
Mortality does not tend to increase any longer: the positive trend results from a lower mortality in young and adult age. Already in the 70's, it progressively reduced amongst the younger ages, and extended to the adult ages over the years, thus affecting the whole cancer mortality.
Cancer mortality reduction is typical of many western, advanced-economy-societies and goes together with recent years' trends of incidence reduction amongst the younger ages.
Table 1.
Number of cancer deaths, estimated new cancer and prevalent cases for all cancers in 1970, 1980, 1990, and 2000. Italy. M+F. Number x 1000
| |
Mortality.
Cancer deaths |
Incidence.
New cancer cases |
Prevalence.
Prevalent cases |
| 1970 |
91 |
149 |
821 |
| 1980 |
115 |
181 |
990 |
| 1990 |
132 |
213 |
1158 |
| 2000 |
138 |
234 |
1294 |
|
Bibliography
(1) Micheli A, Mugno E, Krogh V, Quinn MJ, Coleman M, Hakulinen T, Gatta G, Berrino F, Capocaccia R. Cancer prevalence in European registry areas. Annals of Oncology. 2002 Jun;13(6):840-65.
(2) Verdecchia A, Mariotto A, Capocaccia R, Gatta G, Micheli A, Sant M, Berrino F. Incidence and prevalence of all cancerous diseases in Italy: trends and implications. European Journal of Cancer 2001 Jun;37(9):1149-57.
(3) Capocaccia R, Colonna M, Corazziari I, De Angelis R, Francisci S, Micheli A, Mugno E. Measuring cancer prevalence in Europe: the EUROPREVAL project. Annals of Oncology. 2002 Jun;13(6):831-9
(4) Giles G.: How important are the estimates of cancer prevalence?. Annals of Oncology. 2002 Jun; 13(6):815-6
(5) Tomatis L. Il Cancro: cause, frequenza, controllo. 1990. Garzanti Editore
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