Breast cancer is the leading cause of cancer death in women worldwide, accounting for 23% (1.38 million) of the total new cancer cases and 14% (458 400) of the total cancer deaths in 2008.¹ The incidence rates are higher in developed countries.² In Africa, breast cancer has overtaken cervical cancer as the most common malignancy affecting women, and the incidence rates appear to be rising.³ Although accurate figures regarding the incidence of cancer in Sudan are not available, cancer has emerged as one of the significant health problems.⁴ Breast cancer is the most common hospital treated malignancy, accounting for about one-fifth of all cancers in females. In the Radiation and Isotope Center in Khartoum and the Institute of Nuclear Medicine, Molecular Biology and Oncology (INMO) at Gezira University located in Wad-Madani in Al-Gezira State, 17% (2395/13 924) breast cancer patients from all oncology patients and 21% (732/3547) of breast cancer, respectively, were seen in each institution.^5,6,7 In Sudan, as in the other developing countries, the primary breast cancer risk factors are those associated with urbanisation and economic development, such as earlier menarche, later childbearing, having fewer children, and obesity.⁸ However, the exposure to environmental carcinogens may vary according to social, ethnic, geographic, and occupational factors and may play a role in breast cancer risk in Sudan.

Cytochrome P-4501A1 (CYP1A1) is one of the three-cytochrome P450 family members. It is the critical enzyme in phase I bio-activation of xenobiotics.^9,10 It catalyses many reactions, including cholesterol, drugs, oestrogen and environmental pollutants. In addition, it metabolises several pro-carcinogens into active carcinogens.¹¹ Cytochrome P-4501A1 catalyses catechol oestrogen oxidation to oestrogen semiquinones and quinones. These metabolites are carcinogenic and increase breast cancer risk. These oestrogen metabolites can bind to DNA and result in damage that directly causes genetic alterations and effect tumour initiation.^12,13,14

The CYP1A1 gene has three polymorphisms, which are M1, M2, and M3. Polymorphism M1 is a threonine to cysteine substitution in the 3’ noncoding region. Polymorphism M2 is isoleucine to valine in codon 462 in exon 7. Polymorphism M3 is an A–T to G–C transition mutation in the 3’ noncoding region 300 base pairs from the polyadenylation site. These polymorphisms have been associated with breast cancer risk and have undergone extensive scrutiny.¹⁵

Published data regarding the association of CYP1A1 polymorphism and breast cancer risk reported mixed results.^{16,17,18,19,20,21,22,23} The regions where women live and the environmental exposures to various polyaromatic hydrocarbons and others play a significant role and influence the association between breast cancer risk and CYP1A1 polymorphisms.

In the light of the mixed published reports concerning CYP1A1 polymorphisms and their association with breast cancer risk that vary with region and ethnic groups, we aimed to assess the association of CYP1A1 genetic polymorphisms with breast cancer in women of Afro-Arabian descent from Sudan. Our study is unique as it is the first to be conducted on women of this type of ethnicity.

The study investigated the association of three polymorphic variants of the CYP1A1 gene in Sudanese women with breast cancer and other socio-economic and demographic factors that included menarche, education levels, family history of breast cancer, menopause, and BMI.

Cytochrome P-4501A1 M1 and CYP1A1 M3 genotypes showed no relationship to increased breast cancer risk in premenopausal or postmenopausal ages. African American women carrying the CYP1A1 M1 variant have a significantly higher risk of breast cancer, whilst Nigerian women carrying the CYP1A1 M1 variant had a reduced risk of breast cancer.²¹ There was a non-significant 6% increased risk of postmenopausal women developing breast cancer for carriers of the CYP1A1 M3 (T/C) genotype.²³ In addition there is a significant correlation between M1, M3 and M4 polymorphisms with breast cancer risk in Indian women.²⁵

Our results suggest that CYP1A1 M2 polymorphisms are significantly associated with breast cancer risk in Sudanese women (Table 3). Allele frequency percentages for the CYP1A1 M2 (A) and (G) alleles between patients and the control group were found to be significantly different. The A allele and AA genotype were associated with a reduced risk in the premenopausal group. Furthermore, the G allele and GG genotype were associated with increased risk in this group. We did not observe a similar association in postmenopausal women. Singh et al reported no significant alterations of allelic and genotypic frequencies for M2 when comparing patients with controls based on menopausal state.²⁵ However, we observed a significant protective effect for this allele in postmenopausal women (p < 0.05). Heterozygosity in the CYP1A1 M2 allele had a significant breast cancer-protective effect (OR: 0.33; CI: 0.12–0.89; p-value 0.03) in postmenopausal women. Miyoshi and Noguchi et al investigated the association of two CYP1A1 polymorphisms, that is, 3′ noncoding region (6235(T/C) and codon 462 (Ile/Val), with breast cancer risk in Japanese women.²⁶ Variant allele 6235C carriers at the 3′ noncoding region polymorphism showed a significantly reduced breast cancer risk compared with non-carriers. Variant allele 462Val carriers at the codon 462 polymorphism showed a significantly reduced risk compared with non-carriers. However, CYP1A1 M2 and CYP1A1 M4 are rare in Nigerian women.²³ The differences between Nigerian women and Sudanese women may be related to geographic distribution – Nigerian women are from West Africa, whilst Sudanese women are from East Africa. Sudanese women are of Afro-Arabian descent and may have different genetic make-up and other cancer sustainability genes. A more recent study by Zhang et al reported a significant increase in breast cancer risk in women with the CYP1A1 M2 variant genotype, especially postmenopausal women when compared with women who had the homozygous wild-type CYP1A1 M2 genotype with those harbouring the variant M2 genotype.²⁷ The women with at least one CYP1A1 M2 variant allele had a two-fold increased risk of breast cancer compared with those with homozygous wild-type CYP1A1 M2. The risk became greater amongst postmenopausal women. In women living in Iran, the heterozygote genotype frequency (A/G) significantly increased in patients compared with controls. (A/A) genotype showed a significantly decreased risk of breast cancer. A higher frequency of heterozygotes was mainly observed amongst premenopausal breast cancer patients.^27,28

The present study showed that the education levels, family history of breast cancer, and raised BMI had significant associations with breast cancer risk in Sudanese women. Our findings agree with previously published reports from Sudan and other countries.^29,30,31,32 Recently, several studies reported the association of many reproductive factors, including early age at menarche and late age at menopause, with a high breast cancer risk.^{33,34,35,36,37,38}

In this study, the education level had a significant effect; educated women have a decreased risk of developing cancer. A positive association between the level of education and breast cancer risk is consistent with most but not all previously published studies.³⁹ A family history of breast cancer in a first-degree relative (Table 1) had a significant relationship with the increased risk of breast cancer in Sudanese women. Many studies support that women with a family history of breast cancer run a higher risk of breast cancer than women without a family history.^40,41,42

Patients with BMI ≥ 30 (kg/m²) (BMI: 19 kg/m² – 24.9 kg/m² is considered an ideal weight) comprised about 30% of the patient group, which was significantly higher than that in the controls. On the one hand, several studies support the hypothesis that a higher BMI level may be associated with a decrease in premenopausal breast cancer risk. The results from several case-control and cohort studies supported this hypothesis.^43,44,45,46 On the other hand, a few studies did not observe a statistically significant association when comparing the highest versus lowest levels of BMI.^47,48

There were several limitations to our study; the first concern was the sample size. Studies of this type have not been performed before in Sudan. In addition to the limited studies conducted in Africa, which consisted of a small size, it was challenging to calculate the sample size with reliable power. Therefore, a study with a larger sample size and reliable power may provide more reliable results if conducted in the future. The second limitation is that all the women in the study are from central Sudan and thus do not represent Sudan as a whole. Sudan is a vast country with various ethnic and demographic people, and, therefore, a sample size that includes women from all parts of Sudan is warranted to provide generalisable results. The third limitation of this study is that Sudan is comprised of different environments spanning from the desert in the north to the tropical savanna climate in the south and ranging from developing to under developing populations. Therefore gene-gene and gene-environment interaction may play a critical role in breast cancer development and should be considered when drawing conclusions. Our study did not address ovarian cancer history and radiation exposure because we have examined many other risk factors. Future studies will address other risk factors which were not covered in this study.

In conclusion, our study suggested that the CYP1A1 M2 polymorphism is associated with the risk of developing breast cancer amongst Sudanese patients. The CYP1A1 polymorphism may serve as a potential marker for the diagnosis of breast cancer in Sudan. Despite the limited research capacity and availability of funding to support research in Sudan, we believe our study provides a scientific base and opens the door for genetic polymorphism research for breast cancer in Sudan.