Serum Levels of Selenium and Zinc in Patients with Breast Cancer: A Case-Control Study

Breast cancer (BC), as one of the most common causes of death in the world (1), has distinct pathological and histological characteristics and can be divided into several subtypes based on the presentation of hormone receptors (estrogen receptor (ER) and progesterone receptor (PR)) and the human epidermal growth factor receptor 2 (HER2) (2). Some risk factors including early menarche, late menopause occurred, body mass index (BMI) and obesity after menopause, estrogen intake, alcohol consumption and tobacco use, exposure to ionizing radiation, and eating habits (3), as well as genetic (4-6), environmental factors (5, 6), and ethnicity (7) can effect on the incidence of BC. In various studies, it was found that the serum levels of trace elements in patients with BC have changed and although their role is not fully understood, it may be associated with the risk of this disease (8). Zinc (Zn) is a vital mineral for the operation of numerous cellular processes and growth and may play an important role in malignancy etiology and outcome (9). This mineral has an excessive accumulation in BCs and malignant cell lines compared with normal mammary epithelium (10). Also, it plays a role on the cellular level, the function of transcription factors, and cell proliferation; it defends against radicals and deoxyribonucleic acid (DNA) repair (11). Zn has 4 general biological roles, including structural, signaling, catalytic, and regulatory functions (12). Selenium (Se) is another biotic mineral and a vital micronutrient that has high anti-cancer and chemopreventive properties (13). It is a micronutrient with an essential role in malignancy and has been widely studied as a chemopreventive factor in several experimental models of BC (14). Therefore, because of the importance of Zn and Se in relation to BC and no adequate study in this field in Southeastern Iran, this study aimed at evaluating the serum levels of both elements in the women with BC compared with the control group and the correlation of them with risk factors of BC.

This study was approved by the ethics committee of Zahedan University of Medical Sciences, Zahedan, Iran. Informed consent was taken from the participants. During 2015 to 2016, 142 women with BC (the diagnosis is based on pathology) were referred to the clinic of hematology and medical oncology, Ali Ebne Abitaleb hospital, Zahedan, Iran; they did not have any treatment or it passed more than 6 months from their last treatment. Also, 158 healthy controls, aged 19 to 88 years, were selected for the present study. The participants in both groups did not use any the type of supplement 3 months before the study and they had no history of chronic kidney or liver disease or malabsorption disorders (such as Crohn’s or celiac disease). The BMI was between 18.5 and 30 kg/m² based on the Quetelet index (15) in 2 groups. After recording the demographic and pathology data (according to their medical records), blood samples were collected from both groups. Then, the serum was separated by centrifugation and by maintaining the cold chain and for the assessment of the levels of Zn and Se, it was transferred to the laboratory of Razavi Hospital in Mashhad (Khorasan province in Eastern Iran). Natural menopause was defined as the permanent cessation of menstrual periods, determined retrospectively after a patient had experienced 12 months of amenorrhea without any another obvious pathological or physiological cause, otherwise considered as premenopausal state. Stage was divided to 3 parts based on TNM staging including early stage (stage І [T1N0M0], ІІA [T0N1M0, T1N1M0 or T2N0M0] or ІІB [T2N1M0 or T3N0M0]), locally advanced (stage ІІІA [T0N2M0, T1N2M0, T2N2M0, T3N1M0 or T3N2M0] to ІІІB [T4, any N except N3M0], or ІІІC [Any T, N3, M0]) and metastatic (ІV [Any T, any N, M1]) (16).

The Se was atomized by graphite furnace, in 2300°C and the wavelength of 194 nm. Consumption standard (Se standard Art No: Hc946651, Merck Co., Germany) was used in concentrations of 50 to 500 µg/mL. Also, we used the standard edition method and the palladium chloride as a Matrix Modifier. Zn was atomized by flame, heated up to 800°C and at a wavelength of 314 nm. Consumption standard (Zn standard Art No: Hc62775, Merck Co., Germany) was used in concentrations of 250 to 2000 µg/mL. The amount of these elements was measured and recorded by the atomic absorption device 240 (AA240, Varian Co., Australia). The ER, PR, and HER2 statuses were evaluated by immunohistochemistry (IHC); ER and PR were positive, if they had > 10% positive in tumor cells. For the patients with HER2 2+, chromogenic in situ hybridization (CISH) test was done if the result was 3+ (HER2 positivity) and 2+ (HER2 negativity).

The data was analyzed by SPSS version 11.0; t test was used to compare the mean elements in 2-way variables and One-way ANOVA test was used for 3-way variables (grade and stage). P value < 0.05 was considered to be statistically significant.

The mean age at diagnosis of the patient group was 48.71 ± 1.87 years and the control group was 46.86 ± 13.59 years. The mean Zn was 689.57 ± 146.13 mg/dL in the patient group and 874.85 ± 150.53 mg/dL in the control group; the mean was significantly more in the control group compared with the patient group (P < 0.001) (Table 1). Also, the mean Se was 101.24 ± 17.27 mg/dL in the patient group and 115.36 ± 13.31 mg/dL in the control group; the mean was significantly more in the control group compared with the patient group (P < 0.001).

Table 2 shows the prevalence of several clinicopathological variables in the patient group. Out of 142 patients, 92 (64.8%), 84 (59.2%), and 45 (31.7%) had ER-, PR-, and HER2-positive, respectively. Also, 90 (63.4%) patients were post-menopausal and 13 (9.2%) had a familial history of BC. Thirty-four (23.9%) patients had early stage, 86 (60.66%) locally advanced, and 22 (15.5%) metastatic stage. Fifteen (10.5%) patients had grade Ι, 82 (57.8%) grade ΙΙ, and 45 (31.7%) grade ΙΙΙ.

The comparison of Zn and Se levels with a number of variables in the patient group has been shown in Table 3. There was no a significant difference between elements levels with variables, except for the correlation between stage and Se level in patients; therefore, Se level was lower compared with 2 other stages (P = 0.028).

It has been suggested that oxidative stress produced through either increased free radical generation and/or a reduced antioxidant level in the target cells and tissues may play a main role in carcinogenesis (17). The vital elements such as copper, Zn, and Se are connected together in cytosolic defense against reactive oxygen and nitrogen species (18). Human and laboratory studies have been conducted on the role of these 2 elements in preventing carcinogenesis process and tumor cell growth (19-22). On the other hand, epidemiological studies have shown that differences in dietary habits or diet (23, 24) and air pollution (25) can effect on risk of BC, in line with genetics (26). In Ku‘s study, it was suggested that change the vital elements in serum and tissue might be beneficial and considerable biomarkers in BC (27). Also, Wu et al. (28) reported that there was a significant difference in concentrations of 13 elements in serum between patients with BC and controls, the most important of which were Cadmium, Manganese, Iron, Chromium, and Zn. In this study, the serum levels of Zn and Se was significantly lower in patients with BC compared with the control group; regarding Zn, the results of this study were in line with the results of studies conducted by Pavithra et al. (29) in India and Yucel et al. (30) in Ankara, Turkey; also, regarding Se, result of this study were in line with the results of the studies in Iran (31), Spain (32), India (33), Greece (34), and Nigeria (35).

Holtkamp et al. (36) reported that plasma Zn in patients with BC was decreased according to the stage of the disease and, therefore, in patients with metastatic disease, plasma Zn concentrations were in the lower region of the normal range (mean ± SD: 84.9 ± 21.6 µg/dL), whereas patients with no metastatic BC had normal Zn levels (mean ± SD: 126.0 ± 27.7 µg/dL), and the difference between 2 groups was highly significant (P = 0.001). Zhang et al. (37) reported that low Se-binding protein 1 (SELENBP1) expression in ER-positive patients with BC was significantly associated with a poor survival, and SELENBP1 levels progressively reduced with advancing clinical stages of BC. There was a trend towards the decreased expression of SELENBP1 from stage II (5.62 ± 2.48) to stage III (5.06 ± 2.34), but it did not reach the statistical significance due to limited sample size. One study (13) suggested that organic Se supplementation may reduce/delay BC metastasis. In this study, with increasing the stage, mean Se and Zn was reduced, but this correlation has been just significant for Se. Riesop et al. (38) showed that Zn levels in carcinomatous tissues had a direct correlation with the histological malignancy grade that was almost similar to the result of this study, but the correlation was not significant. Kowalska et al. (39) reported that oral Se was a good candidate for chemoprevention in women, who had BRCA1 gene mutation. One study demonstrated that the Se was as a chemopreventive factor for high-risk BC women or as a therapeutic strategy for ER-positive BC (40). Therefore, differences in the levels of Se and Zn in patients with BC can be because of the prevalence of tumor markers or risk factors as well as genetics and ethnicity.

In conclusion, decreasing the serum levels of Se and Zn may be the risk factors for BC. It seems that adding micronutrients of Zn and Se in patients with serum low levels may reduce the risk of BC. In addition, the role of pathological and genetic factors and their relationship with these 2 elements in the process of treatment may be considered.