Assessment Of Factors Associated With Breast Cancer Among Women In Nyeri County, Kenya - A Case Control Study

Abstract

Introduction: Breast cancer is the most common cancer in women in Kenya (Mulemi, 2010) andthe second most common cancer among women in Nyeri County (HISR 2009), only second tocervicalcancer. It is the most common cause of cancer-related mortality and morbidity among allwomenin the world and the commonest cause of cancer deaths in United States of America amongwomen aged 20 to 59 years (Jemal et aI, 2005). Research has long recognized risk factors forbreastcancer such as a positive family history of breast cancer, early menarche, late menopause,nulliparity and lack of breast feeding (Newcomb et aI, 1994; McTiernan et aI, 1992; MacMahonet aI, 1973; Gunnar et aI, 1987; Roxanne Nelson et aI, 2009). While numerous studieshave been conducted in industrialized countries to assess the epidemiology of breast cancer,few have been done in Sub-Sahara African populations; Kenya included (Mutuma and Korir2006). Such studies are of interest because different risk profiles may help to explain the differencesin occurrence of the disease in different populations. This study is therefore aimed at determiningthe risk factors for breast cancer in Nyeri County, central Kenya. Method:A matched (1:3) case-control study was conducted in Nyeri County of central province inKenyain the year 2010. Data collection was done between March and May 2010 where a total of81 biopsy/fine needle aspiration proven cases of breast cancer and 272 controls that were matchedby age within a 5 year period interval were enrolled. Statistical analysis was carried out usingStata version 10.0 software where chi square test of significance and then logistic regressionwith odds ratios at 95% confidence intervals were estimated. Results:Data analysis showed the following independent risk factors that were predictive for breastcancer among women under study; family history of breast cancer and any other cancer, ageat menarche, menstrual pattern, menopausal status and age at menopause. xv Thosewomen in the study who had no first-degree family history of breast cancer were reported to be76%(OR=0.24, 95% CI: 0.11-0.55) less likely to have breast cancer compared to those whohad a family history of the disease in univariate analysis and 83% (OR =0.17,95% CI: 0.05- 0.56)in multivariate analysis respectively, p < 0.05. Equally, women with no first-degree family historyof other cancer apart from breast were reported to be less likely to have breast cancer comparedto those women with positive first-degree family history by 64% (OR=0.36, 95% CI: 0.20-0.66)in univariate and 73% (OR = 0.27,95% CI: 0.10-0.68) in multivariate analysis respectively,p < 0.05. Pre-menopausal status and late age at menopause (~ 50years) were reported to be protective factorsand statistically significant in univariate analysis with an OR = 0.55 (95% CI: 0.33-0.90) andOR= 0.22 (95% CI: 0.05 - 0.94) respectively, p < 0.05. Early age at menarche was not statistically significant, p > 0.05. However, contrary to other studies late menopause ~ 50 was shown to reduce the risk of breast cancer among the women, while late age at menarche increased the risk. For menstrual pattern, in univariate analysis, the risk of developing breast cancer increased 3- fold in women with irregular menstrual pattern compared with women with regular menses, (OR = 2.88,95% CI: 1.45 -5.70), P < 0.05. The risk changed to increase by 1.5-fold in multivariate analysis, but not statistically significant. Conclusions: This study revealed the role of some modifiable determinants of breast cancer that can be focused on by public health intervention in Nyeri district. Accordingly, those women who have one or more of the following risk factors should be followed up keenly and screened regularly for breast cancer: positive family history of breast cancer and other cancers. The role of XVI hormone replacement therapy, irregular menstrual pattern, age at menarche and menopausal status as risk factors for breast cancer should be investigated further.