Cancer is the second important cause of death worldwide, with 18.1 million new cases and 9.6 million deaths in 2018[1–3]. Evidence from  estimates disclosed that 19.3 million new cases of cancer and approximately 10.0 million cancer attributed deaths occurred worldwide in 2020. The most common cancers diagnosed worldwide were breast cancer (2.26 million cases), lung cancer (2.21) and prostate cancer (1.41), and the most common causes of death were lung cancer (1.79 million deaths), liver cancer (830000) and stomach cancer (769000). It is estimated that the number of newly diagnosed cancer patients will increase to 27,500,000 by 2040, and 16,300,000 patients will die . Cancer is also one top health priority in Iran. According to a national report on cancer registration by Iran’s Ministry of Health and Medical Education (MoHME) (2021), in 2017–2018, the number of new cancer cases in Iran was 134,704. 64,788 (48%) cases occurred in women and 6,916 (52%) of cancers in men. According to this report, the crude incidence rate and the standardized age incidence of all cancers in the country's total population were 166.54 and 168.56 per 100,000 people, respectively. The most common cancers in the population were breast, prostate, colorectal, skin (non-melanoma) and stomach cancers. Also, 55,785 cases of cancer deaths were reported in Iran in 2018 . Figure 1 illustrates the geographical distribution map of the standardized age incidence rate for all cancers in Iran in 2018. A gloomier color indicates a higher incidence. Two central provinces of Iran (Isfahan and Yazd) had the highest standardized cancer incidence in 2018. In contrast, south Khorasan, Lorestan, Zanjan, Sistan-Baluchestan and Hormozgan showed the lowest incidence rate.
Figure 2 demonstrates the age-specific incidence for the five most common cancers in Iran for 2018. Almost all cancers show rapid growth from the age of 50. Only the incidence of breast cancer has accelerated from an early age.
The number of new cancer cases in Iran is expected to increase from 112,000 registered in 2016 to 160,000 in 2025. That means an increase of 42.6 percent. 13.9 percent and 28.7 percent, respectively, will be due to the risk and population structure changes. In terms of specific cancers, the most significant increase is predicted in the thyroid (113.8%), prostate (66.7%), breast (63.0%) and colon (54.1%). Breast, colorectal and stomach cancers were the most common cancers in Iran in 2016, and it is predicted that by 2025, they will remain the leading cancers in the country. The increasing trend in the incidence of more common cancers in Iran reinforces the need for proper national design and implementation. Modirian et al. reported 1025,443 years of life-adjusted life with cancer (DALY) in Iran, with gastric cancer having the largest share in DALY. Rahmani et al. reported esophageal cancer burden in Iran from 1374 to 1394 74399 DALY. One concern of health policymakers in disease control at the national level is how diseases are distributed in terms of the socio-economic characteristics of regions. Socio-economic determinants can affect population health. The World Health Organization (WHO) (2008, 2019) identifies social determinants as factors such as age and circumstances in which individuals are born, raised, live, work and disease control systems formed based on the distribution of money, power and global, national and local resources [12, 13]. Siegel et al. (2019) state that despite a dramatic decline in overall cancer mortality rates from 1991 to 2016, social and economic inequalities in cancer deaths have increased in the United States. It is identified that socio-economic status (SES), race, ethnicity, and residence have been causes of social inequalities in various cancer outcomes. For example, a systematic review of eight studies by Redondo-Sánchez et al.  found that people with lower socio-economic status appear to have a higher chance of developing lung cancer and death than those of higher socio-economic class. Patients in the lower socio-economic class also have lower cancer survival. Mihor et al.  also confirm in their study that belonging to low SES increases the risk of cancers of the head and neck, esophagus, liver and gallbladder, pancreas, lungs, kidneys, bladder, penis and cervix. Alcaraz et al.  have presented the social determinants of cancer equity as the conceptual framework of Fig. 3.
Given the importance of socio-economic factors in the burden of cancer, we aimed to study the distribution of cancer incidence based on the socio-economic characteristics in Iran' provinces.