The present study evaluated risk factors associated with incidence of breast cancer in two groups of female patients with breast cancer and healthy women. According to the results of this study, four latent classes were identified for patients and healthy women. In this study, the majority of subjects in both groups fell under general population risk class. OCP use in general population risk class, and skipping breastfeeding and being single in moderate risk class, were more likely in both study groups.
However, the prevalence of general population risk class was much higher among healthy women compared to breast cancer patients. In general, the pattern of risk factors between the two groups was not different in class 1 and 2, whereas, the pattern of risk factors was different between the two groups in class 3 and 4. In class 3, parity and skipping breastfeeding were more likely among healthy women. However, obesity was more likely to occur in breast cancer patients. In class 4, parity, OCP use, and skipping breastfeeding were more likely to occur in breast cancer patients, while late age at first birth was more likely to occur in healthy women. In this study, we also found that, obesity was exclusively associated with class 3 membership among breast cancer patients, while in healthy women, this variable showed no impact on risk factors clustering.
To the best of our knowledge, this has been the first study focusing on the clustering of breast cancer risk factors based on LCA approach in Iran. However, here we discuss a number of studies that used almost the same method used in our study. Lifestyle patterns in women with breast cancer were assessed using LCA. In this study, three latent classes were identified, including healthy behavior and diet pattern (Class 1), healthy behavior and unhealthy diet pattern (Class2), and unhealthy behavior and diet pattern (Class 3)(18). Zhang et al. examined the relationship between body composition and risk of breast cancer in Chinese women, and identified four classes: Low Muscle Mass (Class 1), High Body Composition (Class 2), High Fat (Class 3), and Normal Body Composition (Class 4)(19) .
The results of our study suggest that OCP use had important role in the clustering of breast cancer patients. This factor had high probability of being present in latent class 1 and 4. Bethea et al. have also shown that the OCP use, especially long-term use, was associated with an increased risk of breast cancer(20). Use of OCPs is associated with increased risk of breast cancer due to the direct elevation of estrogen levels and the role of progesterone in gaining weight indirectly (21). Our study indicated that healthy women in class 1 were also more likely to consume OCP. Therefore, it seems that this risk factor can also cause problems over time and co-occur with other risk factors in healthy women, leading to development of breast cancer in these individuals.
We found a relationship between breast cancer and family history of this cancer. The results of previous studies showed that family history of breast cancer was a well-established and significant risk factor associated with breast cancer(22, 23). Family members share genes and common genetic factors, which may explain the link between family history of breast cancer and increased risk of this cancer. These genetic factors constituted of mutations in genes, such as BRCA1 and BRCA2. Family members also have environments and lifestyles in common, which can increase the risk of breast cancer in women with a family history(24). However, family history was not linked with the clustering of patients and healthy individuals, and probably the effects of other variables were more significant on the subgrouping of women in this study.
Increased parity may defer the onset of breast cancer and inhibit the metastasis of axillary lymph node (ALN)(25). Also, hormonal factors, including estrogen and progesterone may affect the risk of breast cancer, and ultimately changes in these hormones have a major impact on protection against this cancer(26). In an animal study, Yuri et al. found that exposure to estrogen and progesterone in animals during pregnancy protected breast tissue against cancer(27). The results of the present study showed that parity was significantly associated with risk of development of breast cancer. In the pattern of risk factors, this variable also played an essential role in the classification of patients, as the probability of the occurrence of parity was high in two classes. However, it should be noted that among healthy women, parity was more likely to be a warning signal for developing risk factors for this cancer in healthy women in the moderate risk and semi moderate risk classes.
Our findings indicate that skipping of breastfeeding was associated with development of breast cancer. This factor also was likely to occur among breast cancer patients in the moderate risk and high risk classes. The results of a review study showed that breastfeeding significantly reduced the risk of breast cancer in young women(28). Breastfeeding period has been also shown to be associated with hormonal changes and changes in breast tissue, which may reduce the risk of breast cancer, reduce the menstrual cycle and ovulation timing through reproductive life, resulting in reduced exposure to rapid hormonal changes(29, 30). However, skipping breastfeeding was more likely in healthy women in the moderate risk and semi moderate risk classes, thus the co-occurrence of this variable with other risk factors can increase the risk of breast cancer. Probably, the interaction and simultaneous influence of several factors is required for the disease occurrence.
We found that being single was associated with breast cancer. Many studies have proposed various reasons indicating married patients as a better prognosis of breast cancer. As such, these people generally have richer financial resources that support them to perform examinations earlier and more frequent. In addition, in married women, due to having more psychosocial support compared to singles, a better prognosis of the disease was observed, as reduced psychological support and stress is associated with tumor progression and immune deficiency(31, 32). In addition, single women may have poor health habits and behaviors. For example, the results of a study showed that smoking and poor health examinations were more common in single women than in married women(33) .