Introduction
The burden of disease analysis is a method that can integrate the fetal and non-fetal data and provide a summary measure named the disability-adjusted life years, which indicates the total number of years lost as a result of premature death or disability [2]. Considering the high prevalence of cancers in the elderly group and that awareness of the risk factors attributed to cancer can help in macro-level planning in prevention, the present study was designed to calculate the burden of risk factors attributed to common cancers in the elderly living in Markazi Province of Iran in 2016. The results can help the officials and policymakers in the field of health to develop healthy lifestyle programs and cancer screening programs in this region.

Methods
This is a retrospective descriptive-analytical study. The data of older people with cancer or those who died from cancer aged >60 years and lived in Markazi Province for more than 6 months were selected using a census method over one year. These data included: Cancer incidence rate by age group, cancer death rate by age group, average age of cancer death, average age of onset of cancer and average duration of the disease by age and sex groups, standard life expectancy, average age of onset of cancer using patient data available in death registration system, duration of the disease from the time of infection to the time of death or (in rare cases) recovery and the data of the risk factors for cancer using the death registration system and the last national cancer survey report in 2017. The data were first processed in Excel software and were then entered into DisMod II software and the necessary calculations were performed. Cancer diagnosis criteria in this study were based on the 10th version of the international statistical classification of diseases. Demographic information was obtained from the website of the Iranian Statistics Center, and risk factors were extracted from the cancer registration system. The Equation 1 was used to measure the effect of each risk factor on each type of cancers in the elderly [3]:


In this equation, PIF is the potential impact fraction, Pi is the observed prevalence of the risk factor i, pi is the counter factual prevalence of the risk factor i, and RRi is the relative risk of i.

Results
Based on the census report of 2016 in Iran, the population of Markazi Province was estimated at 1429475 people, of whom 155695(10.9%) had 60 years old or higher. There were 1769 new cases of cancer in the province in 2016, of which 1011(57.15%) occurred in the elderly group (Table 1).


In calculating the burden of different risk factors for different types of cancer, the results showed that:
For skin cancer, the highest burden was related to exposure to sunlight (526.71), while the lowest burden was attributed to alcohol consumption (95.22).
For gastric cancer, the highest burden was related to family history (79305.88), while the lowest burden was related to alcohol consumption (2676.23).
For colon cancer, the highest burden was related to not consuming fruits (4063.18), while the lowest burden was related to obesity (408.87).
For breast cancer, the highest burden was related to not being married (6488.58), while the lowest burden was related to the age of menstruation (49.91).
For lung cancer, the highest burden was related to smoking (2646.53), while the lowest burden was related to not consuming fruits (37.14).
For bladder cancer, the highest burden was related to family history (10194.71), while the lowest burden was related to having a high-risk job (109.91).
For ovarian cancer, the highest burden was related to obesity (13129.21), while the lowest burden was related to alcohol use (81.88).
For prostate cancer, the highest burden was related to a history of previous diseases (7244.08), while the lowest burden was related to lack of physical activity (1656.59).

Conclusion
The findings of the present study showed that exposure to sunlight, family history, lack of fruit consumption, lack of marriage, smoking, obesity, and history of previous diseases are the most common risk factors for skin, gastric, colon, breast, lung, ovarian, and prostate cancers. In the present study, the burden of skin cancer was lower compared to other cancers, which can be due to its proper treatment, as well as its better response to treatment and longer life expectancy of patients. Оshyvalova also showed that the non-use of sunscreen and family history were the greatest risk factors for skin cancer [4]. In our study, the highest burden for gastric cancer was family history, while the lowest burden was related to alcohol consumption. In a systematic review study in 2018, Yousefi et al concluded that several factors, including diet, lifestyle, and level of education and awareness of patients, have a role in the risk of gastric cancer [5]. The findings of Lewandowska et al. in 2022 showed that obesity, low physical activity, active and passive smoking, and high consumption of salt and red meat were associated with an increased risk of colon cancer [6]. This is consistent with our results. In the present study, the highest burden of breast cancer was attributed to not being married, family history, and infection, while the age of menstruation had the lowest burden for breast cancer. The findings of a study in 2021 showed that factors such as body mass index, age, and number of births were among the most important factors affecting breast cancer [7].

Ethical Considerations
Compliance with ethical guidelines
To consider the ethical principles, the personal information of the patients was kept confidential. This study was approved by the Ethics Committee of the University of Social Welfare and Rehabilitation Sciences (Code: IR.USWR.REC.1396.326).

Funding
This study was extracted from the PhD dissertation of Ahmad Amani, approved by Department of Geriatrics, School of Social Welfare, University of Social Welfare and Rehabilitation Sciences, and was funded by the University of Social Welfare and Rehabilitation Sciences.

Authors' contributions
Methodology, investigation, funding acquisition, resources and writing the original draft: All authors; Conceptualization, supervision, review & editing: Ahmad Ali Akbari Kamrani.

Conflicts of interest
The authors declared no conflict of interest.


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