METHODS
The data on cancer-related mortality in Turkey from the database of the Turkish Statistical Institute
(TurkStat) were obtained and analysed with the JRA method. Age-standardized mortality rate (ASR),
annual percent change (APC) and average annual percent change (AAPC) were calculated and compared
according to gender.
RESULTS
In female patients, the significant increase in mortality trends were observed in breast, gastrointestinal
system (liver, pancreas, and colon) and gynecological cancers (ovarian and corpus uteri). In male
patients, liver, pancreas, colon, lip, oral cavity, pharynx and bladder cancers were shown to increase
significantly. There was no significant increase in other cancer sites.
CONCLUSION
To our knowledge, this study is the first study that has analyzed cancer and cancer-related death trends
using JRA at the national level in Turkey. We think that our study can demonstrate the contrast trends in
cancer rates. According to these results, better health interventions could be developed to fight against
cancer and to reduce the incidence of cancer-related morbidity and mortality.
Keywords: Cancer; joinpoint regression analysis; mortality; Turkey
The increasing number of deaths due to cancer is
responsible for its high mortality worldwide. In 2012,
there were 8.2 million cancer-related deaths all over
the world. The most common causes of cancer-related deaths were respiratory and gastrointestinal system
cancers.[
In modelling trends over time, many statistical
methods have been developed to detect the changes in
cancer trends and deaths. One of them is the joinpoint
regression method that is used to detect changes and
determine the trends between joinpoints. Cancer not
only causes morbidity and mortality in patients with
cancer but also causes economic burden on countries.
Therefore, planning prevention programs against cancer
and evaluating their efficiency by monitorization of
changing trends on cancer statistics, especially mortality,
are highly important for countries. Herein, our goal
is to reveal alterations in the cancer-related death rates
in Turkey (2009-2017).
The number of deaths for each cancer site was presented according to gender and age [year] (age categories: 0-4, 5-9, 10-14, 15-19, 20-24, 25-29, 30-34, 35- 39, 40-44, 45-49, 50-54, 55-59, 60-64, 65-69, 70-74 and ≥75years).
Statistical Analysis
The first step is applying the simplest model to the
data (e.g. for cancer rates) on a log scale using this formula:
ln (age-adjusted death rate)=a+bx, where x represents
the age of death. APC is computed as [100*(eb
-1)]. APC is statistically significant if its confidence interval
does not contain the zero value. Since our study
included nine years, we allowed only two points as a
maximum number for analysis.[
JRA is a statistical modelling approach, which is generally
used for modelling the time trends in a data set.
JRA begins with the minimum number of joinpoints
and tests whether one or more joinpoints are statistically
significant and should be added to the model. The
number of joinpoints is determined by Monte Carlo
permutation tests.[
One joinpoint model (in 2003) was obtained as the best-fit model for female deaths rates in the stomach and larynx-lung-bronchus cancers. ASRs from stomach cancer were shown to increase by 1.8% per year from 2009 to 2014, and to decrease significantly by 4.5% per year after 2014. ASRs from larynx, lung and bronchus cancers also were shown to have a significant increase trend from 2009 to 2015, followed by a decline between the years 2015-2017 (APC: -2.4).
In other cancer sites, the zero joinpoint model was determined as the best model. A steady, significant increase was observed in six cancer sites: colon, liver, pancreas, breast, corpus uteri and unspecified, ovary during the analysis period (2009-2017).
In Turkey, the government has also adopted precautions
nationally. Turkey bridges between Asia and
Europe geographically. As mentioned before, the risk
of cancer varies according to genetic risks, regional
variations, lifestyle and environmental risk factors.
Therefore, cancer types vary in the West and East Regions
of Turkey.[
To our knowledge, this study is the first epidemiological
study analysing the cancer trends in Turkey using the JRA method. This study also has the importance
of being the most actual analysis investigating
the cancer deaths within the country. The used analysis
in this study, namely the JRA is usually applied
to analyse varying trends over time. In addition to
providing important baseline data on present cancer
deaths, this study also demonstrates contrasting
trends in cancer rates over the past nine years. Our
study is an answer to the question of whether cancer mortality trends are increasing or decreasing over the
years in Turkey.
According to our analysis, the three leading causes
of cancer-related death in male patients were lung,
gastric and haematological cancers. The leading cause
of cancer-related mortality on male patients was lung
cancer. In females, breast cancer was the leading cause
of cancer-related deaths. The next leading causes were
respiratory system and haematological cancers. While
ARSs of colon, liver and pancreatic cancers were equal
(over 20%), head and neck cancers had the highest increase
in males, whereas pancreatic cancers had the
highest increase in females.
As shown in Table 2, ASRs of head and neck cancers
decreased between 2009 and 2015 among male
patients, whereas between 2015 and 2017, ASRs of
head and neck cancers increased according to a single
joinpoint model. ASRs of colon cancer increased between
2009 and 2014, and after that, a decrease started
significantly. Similarly, ASRs of respiratory system cancers
showed an upward trend between 2009 and 2013,
followed by a significant decline between 20132017.
According to these results, a single joinpoint model is
found to be the best-fit model for male death rates in
these cancers.
For other cancer sites, the zero joinpoint model was
determined to be the best model. A steady, significant
increase was observed in only three cancer sites (liver,
pancreas and bladder) during the nine-year period of
2009-2017.
As known, one joinpoint model was the best model
for female death rates in some cancers. ASRs of gastric
cancer increased in the first five-year period (2009-14),
then, decreased in the second four-year period (2014-
17). ASRs of respiratory system cancers showed a significant
upward trend from 2009 to 2015, followed by
the decline for the period of 2015-2017.
In other cancer sites, the zero joinpoint model was
determined to be the best model. A steady, significant
increase was observed in six cancer sites (colon, liver,
pancreas, breast, corpus uteri and unspecified, ovary)
during the whole analysis period (2009-2017).
Limitations of the Study
No mortality data were unavailable before 2009 to
compare. No comparisons were available according
to regional differences, which is important as the percentages
of cancers differ according to geographical
regions. The other limitation was the short analysis period.
In general, change in rates in morbidity and mortality
of cancers is a long-lasting process.
Peer-review: Externally peer-reviewed.
Conflict of Interest: The authors declare no conflict of interest.
Financial Support: No financial support has used for the study.
Authorship contributions: Concept - N.D.; Design - N.D., T.K., İ.D.; Supervision - N.D., T.K., İ.D.; Funding - None; Materials - None; Data collection and/or processing - N.D., İ.D.; Data analysis and/or interpretation - N.D., T.K., İ.D.; Literature search - N.D., T.K., İ.D.; Writing - N.D., T.K., İ.D.; Critical review - N.D., T.K., İ.D.
