In Iran, along with worldwide, breast cancer is one of the most frequent cancers [4]. We performed a case-control study involving 800 Iranian women to evaluate the relationship between breast cancer and such risk factors as socio-demographic, reproductive, chronic diseases, and behavioral habits.
As shown in Table 1, we found that more than 48% of patients were younger than 50 years, patients were between 41–50 years, which is in line with results of Akbari et al. study [4]. This confirms breast cancer patients in Iran are relatively young and breast cancer occurs a decade earlier in Iranian women in comparison with women of western countries [15]. In addition, our study provides additional support for a great risk factor for patients living in urban regions, a finding that is consistent with previous studies [16, 17]. Breast cancer shows a large urban-rural difference worldwide [18]. Due to differences in lifestyle, dietary choices, and the environmental pollution in urban life, it was considered as a risk factor for breast cancer incidence in contrast to rural life factor [14, 19, 20]. In contrast, in a study conducted on Chinese women by Liu et al. the converse results were reported, where the rural life was considered as a risk factor for breast cancer [11].
Weight gain increases the risk of breast cancer [21]. Weight loss in early adulthood and after menopause is related to reduced breast cancer risk [22, 23]. In contrast, it was confirmed that excess body weight protects against premenopausal breast cancer risk [24]. Our study showed no significant relationship between weights and breast cancer. Besides, previous studies showed that taller women have a higher risk of breast cancer than shorter women [25, 26]. But in our study, there was a significant association between height status of short and the risk of breast cancer. Further studies are needed on the association between height and the risk of breast cancer. High values of BMI are associated with increased risk of breast cancer after menopause [27, 28]. Similar to previous reports, we found an association between increasing BMI and the risk of breast cancer [11, 13]. This is probably due, in part, to higher estrogen levels because fat tissue is the largest source of estrogen in postmenopausal women [22].
The findings of various studies on the relationship of levels of education and breast cancer risk are controversial, but some studies have suggested an association [29, 30]. We found a correlation between low levels of education with an increased risk of breast cancer. In contrast, it was reported that there is no relationship between education status and risk of breast cancer [13, 31]. In keeping, in consistent with Liu et al.[11], we also showed a statistical significance difference between awareness level with risk of breast cancer. The high level of awareness about risk factors related to breast cancer and screening may help to prevent/ reduce the risk of breast cancer [32]. Women’s job is another factor that we involved in our study and showed a significant association between job status and breast cancer, supporting the results of previous studies [33, 34]. Women in professional and managerial jobs have 1.4-2.0 times greater risk of breast cancer than women in lower-status jobs [35]. A case-control study conducted by Chatchai et al. [36] reported an increased risk of breast cancer in women who worked in manufacturing, transport equipment operators and laborers. There was a significant association between the job status of the employee and the risk of breast cancer. In another word, the job status of the employee is associated with a reduced risk of breast cancer. Researchers believe that employee women generally have higher income and are more likely to use health insurance and spend the most on healthcare [37]. However, it seems that the association of job status with risk of breast cancer remains unknown or controversial [38, 39]. This needs further investigation. It was suggested that higher economic status is associated with increased breast cancer risk [40]. In contrast, our result suggested an association of the economic status of the poor with breast cancer that is consistent with data of Liu and co-workers [11].
The association between reproductive risk factors and breast cancer has previously been reported [41]. As can be seen in Table 2, we found the early menarche increased risk of breast cancer. Correlation between early menarche and increased breast cancer risk may be attributed to the earlier exposure and higher levels of estrogen experienced by women who had early menarche [42]. The results of our study on the age of menarche are consistent with other studies [42, 43]. Breast cancer risk increases with later menopause [44]. Women who experience menopause at age 55 or older have about a 12% higher risk compared to those who do so between ages 50–54 [45, 46]. In our study, we found no significant association between breast cancer risk and late menopauses. This is in good agreement with previous studies [29, 31]. In case of the marital status, in consistent with previous reports [13, 33], we demonstrated that there was no relationship between the marital status with the risk of breast cancer. However, others found a significant correlation between marital status and breast cancer [47].
A growing body of evidence showed that single women have a higher risk of breast cancer than married women [48]. Married, divorced, and widowed women have no inherent differences in their risk of breast cancer than with single women, and that the apparent protective effect of marriage maybe because of the age of their first pregnancy and childbirth [31, 49]. Nulliparous women are more at risk to attain breast cancer than those who have given birth many times. Women having children have 30% reduced risk compared to nulliparous women, in other words with each full-term pregnancy, the risk falls overall by 7% [50]. But in our study, as shown in Table 2, there was no association between the number of children (having or not having children) with breast cancer, which substantiates previous findings in the literature [13, 29]. These findings significantly differ from previous results reported in the literature [11, 31].
Use oral contraceptives pills has been associated with increased risk of breast cancer in young women [51, 52]. The International Agency for Research on Cancer came to deduction that there was sufficient evidence to support combined estrogen–progestin oral contraceptives carcinogenicity in humans, with an increased breast cancer risk [53]. In our study, there was no association between the use the oral contraceptives pills and breast cancer that is consistent with previous reports [54–57]. Similarly, we found no association between abortion and breast cancer, which is consistent with previous studies [11, 54]. To best our knowledge, few studies have been conducted on the association between stillbirth and breast cancer. In a study, a significant association between stillbirth and reduced risk of breast cancer was reported [58]. We also found an association between the stillbirths and increased risk of breast cancer [58]. Breastfeeding has a protective role against risk of breast cancer [59]. In the 47 studies in 30 countries, the risk of breast cancer was reduced by 4% for any 12 months of breastfeeding [59]. Breastfeeding considered as an uncertain protective factor due to indecisive results [60]. But we obtained different results so that, there was no significant association between breastfeeding and breast cancer. Our results share a number of similarities with previous findings [11, 54]. It may discuss that marital status by itself is not a decisive factor for reduced or increased breast cancer risk.
We also investigated an association between chronic diseases and behavioral habits and risk of breast cancer. As shown in Table 3, the hypertension was not associated with breast cancer risk. Our data is consistent with studies conducted by Wang et al. [61] and Sun et al. [62]. One cohort study, one nested case-control study and ten case-control studies showed that hypertension is associated with increased risk of breast cancer [63]. In addition, in our study, in contrast with literature, there was no significant association between the risk of breast cancer and either diabetes [64–66] or the physical activity [33, 67] and or the smoking status [33, 68]. But we found a significant association between the second-hand smoking and breast cancer, which shares similarity with findings of Reynolds et al. [69]. The majority of studies have shown that a family history of breast cancer is one of the major risk factors [24, 25]. In our study, we demonstrated that the family history of breast cancer, in the first degree relatives and second-degree relative was associated with the susceptibility to breast cancer.
We investigated behavioral habits as a risk factor for breast cancer (Table 3). The positive association between unhealthy dietary patterns (low or no consumption of vegetables and fruits, high consumption of high-fat food, fried food and fast food) and breast cancer has been reported [68]. In our study, we found that a healthy dietary was associated with a reduced risk for breast cancer risk, while an unhealthy dietary pattern was increased the risk of breast cancer. Our finding is consistent with previous reports [70, 71]. Increased consumption of fatty, fried, and fast foods should be replaced with an increase intake of fruits and vegetables so that, it is necessary to raise awareness about healthy diets and reduced risk of breast cancer. In some studies, the role of alcohol carcinogens and its association with breast cancer has been addressed [72, 73]. Numerous studies show that alcohol consumption increases the risk of breast cancer in the female by about 7%-10% for each 10 grams of alcohol consumed per day on average [74, 75]. We found a non-significant relationship between alcohol consumption and breast cancer so that consistent with some studies conducted [11, 76].
Our study has some limitations; since the present study is a hospital-based case-control study rather than population-based, it may make selection bias. In addition, it is notable that this hospital treats a part of the breast cancer cases in Arak, Iran. Most of the data were recorded from the women’s self-reports, thus bias was more possible; thus participants history records were checked.