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      Breast cancer risk after full‐term pregnancies among African women from Nigeria, Cameroon, and Uganda

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          Abstract

          BACKGROUND

          The breast cancer (BC) risk profiles of African women differ significantly from those of women of European ancestry. African women are younger at the age of onset and tend to have high parity. The purpose of this study was to examine the relationship between full‐term pregnancy (FTP) and the risk of BC.

          METHODS

          A case‐control study was conducted among 1995 women with invasive BC and 2631 controls in Nigeria, Cameroon, and Uganda. Odds ratios (ORs) for individual ages at FTP according to the time since delivery were calculated and adjusted for confounders. A fitted spline model was used to assess the impact of the number of pregnancies on BC risk.

          RESULTS

          In comparison with a nulliparous woman, a parous woman with her first FTP at 20 years showed an OR of 0.76 (95% confidence interval [CI], 0.57‐0.99) for developing BC in the following 5 years. Ten years later, this risk was 0.76 (95% CI, 0.58‐0.99) and 0.76 (95% CI, 0.58‐0.98) for women aged 25 and 30 years, respectively. Similarly, a parous woman with 1 pregnancy had an OR of 0.69 (95% CI, 0.49‐0.96), whereas the OR was 0.66 (95% CI, 0.48‐0.91) with 2 or 5 pregnancies and 0.67 (95% CI, 0.47‐0.94) with 6 pregnancies in comparison with nulliparous women.

          CONCLUSIONS

          In contrast to studies in women of European ancestry, this study showed no transient increase in the risk of developing BC after FTP among African women. Further studies are needed to examine the impact of reproductive factors on early‐onset BC in African women. Cancer 2015;121:2237–2243. © 2015 American Cancer Society.

          Abstract

          There is no transient increase in breast cancer risk after a full‐term pregnancy among African women. The protection conferred by pregnancy occurs immediately after the first full‐term pregnancy regardless of the age at that pregnancy and the number of pregnancies.

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          Most cited references31

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          Global estimates of cancer prevalence for 27 sites in the adult population in 2008.

          Recent estimates of global cancer incidence and survival were used to update previous figures of limited duration prevalence to the year 2008. The number of patients with cancer diagnosed between 2004 and 2008 who were still alive at the end of 2008 in the adult population is described by world region, country and the human development index. The 5-year global cancer prevalence is estimated to be 28.8 million in 2008. Close to half of the prevalence burden is in areas of very high human development that comprise only one-sixth of the world's population. Breast cancer continues to be the most prevalent cancer in the vast majority of countries globally; cervix cancer is the most prevalent cancer in much of Sub-Saharan Africa and Southern Asia and prostate cancer dominates in North America, Oceania and Northern and Western Europe. Stomach cancer is the most prevalent cancer in Eastern Asia (including China); oral cancer ranks as the most prevalent cancer in Indian men and Kaposi sarcoma has the highest 5-year prevalence among men in 11 countries in Sub-Saharan Africa. The methods used to estimate point prevalence appears to give reasonable results at the global level. The figures highlight the need for long-term care targeted at managing patients with certain very frequently diagnosed cancer forms. To be of greater relevance to cancer planning, the estimation of other time-based measures of global prevalence is warranted. Copyright © 2012 UICC.
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            Population differences in breast cancer: survey in indigenous African women reveals over-representation of triple-negative breast cancer.

            Compared with white women, black women experience a disproportionate burden of aggressive breast cancer for reasons that remain unknown and understudied. In the first study of its kind, we determined the distribution of molecular subtypes of invasive breast tumors in indigenous black women in West Africa. The study comprised 507 patients diagnosed with breast cancer between 1996 and 2007 at six geographic regions in Nigeria and Senegal. Formalin-fixed and paraffin-embedded sections were constructed into tissue microarrays and immunostained with 15 antibodies. Five molecular subtypes were determined, and hierarchical cluster analysis was conducted to explore subgroups for unclassified cases. The mean (+/- standard deviation) age of 378 patients in the first cohort was 44.8 +/- 11.8 years, with the majority of women presenting with large (4.4 +/- 2.0 cm) high-grade tumors (83%) in advanced stages (72% node positive). The proportions of estrogen receptor (ER) -positive, progesterone receptor-positive, and human epidermal growth factor receptor 2 (HER2) -positive tumors were 24%, 20%, and 17%, respectively. Triple negativity for these markers was predominant, including basal-like (27%) and unclassified subtype (28%). Other subtypes were luminal A (27%), luminal B (2%), and HER2 positive/ER negative (15%). The findings were replicated in the second cohort of 129 patients. The unclassified cases could be grouped into a bad prognosis branch, with expression of vascular endothelial growth factor, B-cell lymphoma extra-large protein, and Cyclin E, and a good prognosis branch, with expression of B-cell lymphoma protein 2 and Cyclin D1. These findings underscore the urgent need for research into the etiology and treatment of the aggressive molecular subtypes that disproportionately affect young women in the African diaspora.
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              Transient increase in the risk of breast cancer after giving birth.

              The effect of pregnancy on the risk of breast cancer is not clear. We tested the hypothesis that the risk of breast cancer increases transiently after pregnancy but then falls to a level below that of age-matched nulliparous women. We conducted a case-control study of a nationwide cohort in Sweden, using a computerized record linkage between the Cancer Registry and the Fertility Registry. The study subjects were women born from 1925 through 1960 who were resident citizens of Sweden at the time of the 1960 census. A total of 12,666 patients with breast cancer were compared with 62,121 age-matched control subjects. We used conditional logistic regression to estimate odds ratios for the development of breast cancer at different ages, according to maternal age at first delivery (in uniparous as compared with nulliparous women) and age at second delivery (in biparous as compared with uniparous women). Uniparous women were at higher risk of breast cancer than nulliparous women for up to 15 years after childbirth and at lower risk thereafter. The excess risk was most pronounced among women who were older at the time of their first delivery (odds ratio 5 years after delivery among women 35 years old at first delivery, 1.26; 95 percent confidence interval, 1.10 to 1.44). Women who had two pregnancies had a less striking increase in risk. Pregnancy has a dual effect on the risk of breast cancer: it transiently increases the risk after childbirth but reduces the risk in later years. In women with two pregnancies, the short-term adverse effect is masked by the long-term protection imparted by the first pregnancy. A plausible biologic interpretation is that pregnancy increases the short-term risk of breast cancer by stimulating the growth of cells that have undergone the early stages of malignant transformation but that it confers long-term protection by inducing the differentiation of normal mammary stem cells that have the potential for neoplastic change.
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                Author and article information

                Journal
                Cancer
                Cancer
                10.1002/(ISSN)1097-0142
                CNCR
                Cancer
                John Wiley and Sons Inc. (Hoboken )
                0008-543X
                1097-0142
                17 March 2015
                01 July 2015
                : 121
                : 13 ( doiID: 10.1002/cncr.v121.13 )
                : 2237-2243
                Affiliations
                [ 1 ] Center for Clinical Cancer Genetics and Global Health, Department of MedicineUniversity of Chicago Chicago Illinois
                [ 2 ] Department of SurgeryCollege of Medicine, University of Ibadan Ibadan Nigeria
                [ 3 ] Department of Epidemiology and Preventive MedicineInstitute of Human Virology and Greenebaum Cancer Center University of Maryland Baltimore Maryland
                [ 4 ]Institute of Human Virology Abuja Nigeria
                [ 5 ] Department of Public Health SciencesUniversity of Chicago Chicago Illinois
                [ 6 ] Center for Population and Reproductive Health, College of MedicineUniversity of Ibadan Ibadan Nigeria
                [ 7 ]Yaounde General Hospital Yaounde Cameroon
                [ 8 ]Mulago Hospital Kampala Uganda
                Author notes
                [*] [* ] Corresponding author: Olufunmilayo I. Olopade, MD, Center for Clinical Cancer Genetics and Global Health, Department of Medicine, University of Chicago, 5841 South Maryland Avenue, MC2115, Chicago, IL 60637; Fax: (773) 834‐1659; folopade@ 123456medicine.bsd.uchicago.edu
                Article
                CNCR29305
                10.1002/cncr.29305
                4573769
                25781581
                5a41c171-457c-4cc2-8dca-a13aab1af4bc
                © 2015 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society

                This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

                History
                : 04 November 2014
                : 22 December 2014
                : 23 December 2014
                Page count
                Pages: 7
                Funding
                Funded by: National Institutes of Health
                Award ID: CA‐RO1 89085‐01A
                Award ID: P50 CA125183
                Categories
                Original Article
                Original Articles
                Discipline
                Epidemiology
                Custom metadata
                2.0
                cncr29305
                July 1, 2015
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.9.4 mode:remove_FC converted:31.08.2016

                Oncology & Radiotherapy
                african,age at first full‐term pregnancy,breast cancer,case‐control studies,parity

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