Knowing cancer incidence trends is of great interest to carry out cancer surveillance and control activities in a population, as it provides information, mainly from two perspectives: primary prevention and planning of healthcare services.
Trends can show variations in population exposure to different risk factors, which will result in an increase or decrease in incidence rates. In those cancers like lung cancer where there is some factor with a very high attributable risk such as smoking, changes in smoking habits of the population will lead to, years later, changes in rates incidence of this type of cancer. Similarly, trends may be influenced by a better population access to health services and improvements in diagnostic and therapeutic techniques, or their application to screening programs that identify cancers which otherwise would have remained undiscovered.
But time trends are also affected by changes in population size and structure by age groups. For this reason, it is important to express trends as crude rates, due to their interest when planning healthcare, as well as standardized rates, which allows comparison between different periods, taking into account changes in the population age structure.
Information on incidence and new cancer cases during the period 1985-2007 in the province of Granada has been provided by the Granada Cancer Registry.
The table below presents information for all cancers, number of cases, crude and standardized (European population) rates by sex and Total Percent Change (TPC), all of it taking the two groups at the opposite ends of the five-year period: 1985-1989 and 2003-2007.
|Source: Granada Cancer Registry, EASP
||TPC: Total Percent Change
From 1985 to 2007, incidence rates for all cancers increased progressively in males and females (both number of cases and crude rates). The total number of incident cases recorded in the province of Granada during the period 1985-1989 rose up to 6701 men and 4735 women and increased to 12,542 men and 9014 women in 2003-2007. The total percent change in number of cases between these two periods was 87% and 90% in men and women respectively. Lower percent changes were observed in crude rates .
This increase is due in part to an aging population, so if expressed as standardized rates, the increase appears smaller (34% and 47% in men and women, respectively).
For a more detailed analysis of incidence trends, a non linear regression (joinpoint regression) model has been used, estimating the annual percent change (APC) and the inflection points in trends.
The figure shows cancer incidence trends in the province of Granada from 1985 to 2006, for all cancers and the six most common cancers in men and women in the last period (2003-2007).
For all cancers, including nonmelanoma skin, there was a statistically significant increase in male and female rates.
The analysis of trends for each one of the cancers under study shows specific patterns
Nonmelanoma skin and colorectal cancer
A statistically significant increase in incidence rates has been observed in both sexes for non-melanoma skin and colorectal cancer.
For bladder cancer, rates increased in males (statistically significant result) and stabilized in females.
Rates increased in the first period and then fell, both facts being statistically significant, with an inflection point being observed in males, and female rates increased over the whole period (statistically significant result).
Prostate and breast cancers
For prostate and breast cancers in men and women respectively, rates increased during the period under study, which was statistically significant.
Uterine and ovarian cancers
Rates increased for these cancers, which was statistically significant.
Population based cancer registries make possible to know cancer incidence trends in a specific geographical area, thus contributing to surveillance and control of cancer in a population.