African Breast Cancer - Disparities In Outcomes Research Articles

Regional Variation in the Tumor Microenvironment, Immune Escape and Prognostic Factors in Breast Cancer in Sub-Saharan Africa.

The low overall survival rates of patients with breast cancer in sub-Saharan Africa (SSA) are driven by regionally differing tumor biology, advanced tumor stages at diagnosis, and limited access to therapy. However, it is not known whether regional differences in the composition of the tumor microenvironment (TME) exist and affect patients' prognosis. In this international, multicentre cohort study, 1,237 formalin-fixed, paraffin-embedded breast cancer samples, including samples of the "African Breast Cancer-Disparities in Outcomes (ABC-DO) Study," were analyzed. The immune cell phenotypes, their spatial distribution in the TME, and immune escape mechanisms of breast cancer samples from SSA and Germany (n = 117) were investigated using histomorphology, conventional and multiplex IHC, and RNA expression analysis. The data revealed no regional differences in the number of tumor-infiltrating lymphocytes (TIL) in the 1,237 SSA breast cancer samples, while the distribution of TILs in different breast cancer IHC subtypes showed regional diversity, particularly when compared with German samples. Higher TIL densities were associated with better survival in the SSA cohort (n = 400), but regional differences concerning the predictive value of TILs existed. High numbers of CD163+ macrophages and CD3+CD8+ T cells accompanied by reduced cytotoxicity, altered IL10 and IFNγ levels and downregulation of MHC class I components were predominantly detected in breast cancer samples from Western SSA. Features of nonimmunogenic breast cancer phenotypes were associated with reduced patient survival (n = 131). We therefore conclude that regional diversity in the distribution of breast cancer subtypes, TME composition, and immune escape mechanisms should be considered for therapy decisions in SSA and the design of personalized therapies. See related Spotlight by Bergin et al., p. 705.

Treatment guideline concordance, initiation, and abandonment in patients with non-metastatic breast cancer from the African Breast Cancer-Disparities in Outcomes (ABC-DO) cohort in sub-Saharan Africa: a prospective cohort study.

Comprehensive breast cancer management is essential to achieve high breast cancer survival; however, detailed reports of the treatment regimens received by patients are scarce in sub-Saharan Africa where survival is low. We aimed to examine treatment initiation, guideline concordance, and abandonment in patients with non-metastatic breast cancer in sub-Saharan Africa from the African Breast Cancer-Disparities in Outcomes (ABC-DO) prospective cohort. The ABC-DO prospective cohort study recruited women (aged ≥18 years) with newly diagnosed invasive breast cancer in eight hospitals across five sub-Saharan African countries (Namibia, Nigeria, Uganda, South Africa, and Zambia). We analysed treatments received by women who were classified as non-metastatic (M0) at the initial presentation. Data on surgery, radiotherapy, and systemic therapies were obtained from medical records and a self-reported follow-up questionnaire at 6 months after the diagnosis, follow-up calls every 3 months, and a baseline questionnaire. Initiation, completion, and abandonment of treatment modalities and combined therapy regimens were examined overall, by country-specific groups, and by clinical factors relevant for guideline-based treatment. Of 2313 women recruited into the ABC-DO study between Sept 10, 2014, and Dec 31, 2017, 2226 had histologically or clinically confirmed breast cancer. Of these 2226 women, 510 were excluded from the present analysis because 378 had metastatic disease, 37 were prevalent cases (defined as those previously diagnosed with breast cancer >2 years before baseline), 82 had unknown TNM stage, and 13 were White or Asian women in South Africa (number was too small for analysis). After a median follow-up of 5·2 years (IQR 4·6-5·9), 1163 (68%) of 1716 women underwent breast cancer surgery. Surgery and systemic therapy (ie, multimodality treatment) with radiotherapy was initiated in 370 (36%) of 1028 women with localised tumours versus 156 (23%) of 688 women with locally advanced tumours, whereas multimodality treatment without radiotherapy was initiated in 386 (38%) versus 167 (24%) women, respectively. Of 1530 patients requiring chemotherapy (which excludes 105 who died within 6 months after baseline), 1013 (66%) initiated treatment of neoadjuvant chemotherapy or surgery within 3 months after baseline, which was adequately completed by 359 (35%) of 1013 women, marginally completed by 284 (28%), abandoned by 200 (20%), and unknown in 151 (15%). 19 (2%) women died within 6 months after chemotherapy initiation. Of 1375 women in whom endocrine therapy was indicated, this treatment was initiated in 920, and lasted at least 3 years in 367 (40%) women. Treatment disparities between country-specific groups were substantial for all therapy regimens. A high proportion of patients with non-metastatic breast cancer did not initiate, did not fully complete, or abandoned treatment with surgery, systemic therapy, radiotherapy, or an appropriate combination of these, highlighting the need for improved treatment access and completion in sub-Saharan Africa to potentially prevent premature breast cancer deaths. National Institutes of Health (National Cancer Institute), Susan G Komen, and the International Agency for Research on Cancer.

Disparities in breast cancer survival between women with and without HIV across sub-Saharan Africa (ABC-DO): a prospective, cohort study.

SummaryBackgroundStudies have shown increased mortality among women living with HIV diagnosed with breast cancer compared with HIV-negative women with breast cancer. We aimed to examine how this HIV differential varies by patient or breast tumour characteristics.MethodsThe African Breast Cancer–Disparities in Outcomes (ABC-DO) study is a prospective cohort of women (aged ≥18 years) with incident breast cancer recruited consecutively at diagnosis (2014–17) from hospitals in Namibia, Nigeria, South Africa, Uganda, and Zambia. Detailed clinical and epidemiological data, including self-reported or tested HIV status, were collected at baseline. Participants were actively followed up via telephone calls every 3 months. The primary outcome was all-cause mortality, assessed in all women who had at least one updated vital status after baseline interview. Using Cox regression, we examined differences in overall survival by HIV status in the cohort, and across country and patient subgroups, adjusted for age, tumour grade, and tumour stage at cancer diagnosis.FindingsBetween Sept 8, 2014, and Dec 31, 2017, we recruited 2154 women with primary breast cancer, 519 of whom were excluded due to their countries having small numbers of women with HIV for comparison. Among the remaining 1635 women, 313 (19%) were living with HIV, 1184 (72%) were HIV negative, and 138 (9%) had unknown HIV status. At breast cancer diagnosis, women with HIV were younger and had lower body-mass index (BMI) than their HIV-negative counterparts, but had similar tumour stage, grade, and receptor subtypes. At the end of the follow-up (Jan 1, 2019), a higher proportion of women with HIV (137 [44%] of 313) had died than had HIV-negative women (432 [37%] of 1184). Crude 3-year survival was 9% lower for women with HIV (46% [95% CI 40–53]) than for HIV-negative women (55% [52–59]; hazard ratio (HR) 1·41 [1·15–1·74]). The HIV survival differential did not differ by age, BMI, tumour subtype, or tumour grade, but was stronger in women with non-metastatic disease (3-year survival 52% HIV-positive vs 63% HIV-negative women, adjusted HR 1·65 [1·30–2·10]), whereas women with metastatic cancer had low survival, regardless of HIV status.InterpretationThe larger survival deficit among women with HIV with non-metastatic breast cancer calls for a better understanding of the reasons underlying this differential (eg, biological mechanisms, health behaviours, detrimental HIV–breast cancer treatment interactions, or higher HIV background mortality) to inform strategies for reducing mortality among this patient group.FundingSusan G Komen, International Agency for Research on Cancer, National Cancer Institute, and UK-Commonwealth Scholarships.

Abstract P3-12-17: Breast cancer treatment related survival gains in the African breast cancer - Disparities in outcomes study

Abstract Background: Breast cancer (BC) survival in Low and Middle Income Countries (LMICs), and particularly Sub Saharan Africa (SSA), is low and incidence rates are increasing. Accordingly, an almost 90% increase in annual BC mortality is projected to occur until 2040. The WHO Breast Cancer Global Initiative named comprehensive breast cancer treatment as one of three main pillars to reduce BC mortality. Here, we present the urgently needed up-to-date benchmark estimates of treatment effects on BC survival in SSA using data from the African Breast Cancer Disparities in Outcomes (ABC-DO) study.Methods: Since 2014 the hospital-recruited ABC-DO cohort follows-up women diagnosed with BC in five SSA countries. Socio-demographic, diagnostic, treatment and mortality data were obtained from medical records and via three-monthly follow-up calls with the patient. Cox proportional hazard models were fitted to estimate 5-year overall survival related to treatment initiation (surgery or systemic therapy) and treatment completion as time varying variates (surgery and systemic therapy completed) stratified by country and ethnicity and separate for localised and regional tumours. All models were adjusted for age, tumour grade, tumour size, node positivity, HIV status, and socioeconomic status. Results: Of 1699 ABC-DO women with invasive non-metastatic BC, 89% initiated BC treatment (from 72% in Nigeria to 100% in South African white women). Potentially curative treatment (surgery plus systemic therapy) was initiated by 63%, 22% initiated systemic treatment and 5 % only surgery. Initiated systemic therapy was completed by 49% of patients (from 16% in Nigeria to 70 % in South African black women). Median time to first treatment was 1.4 (IQR: 0.8–3) months and differed between countries (from 1.1 (0.6–1.7) in Namibian non-black to 3 (1.5–4.3) in Uganda). After 5 years, 49% (0.44 (CI: 0.31 – 0.62) ) of women initiating any treatment and 59% (0.39 (0.27 – 0.56) of women receiving surgery and initiating systemic treatment were still alive compared to 20% of women receiving no treatment. Conclusion: Timely and comprehensive BC treatment are needed to increase the very low survival rates in SSA. Citation Format: Milena Foerster, Eva Kantelhardt, MD, Pauline Boucheron, Isabel dos-Santos-Silva, PhD, Valerie McCormack, the ABC-DO study team. Breast cancer treatment related survival gains in the African breast cancer - Disparities in outcomes study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-17.

Self-reported arm and shoulder problems in breast cancer survivors in Sub-Saharan Africa: the African Breast Cancer-Disparities in Outcomes cohort study

BackgroundArm and shoulder problems (ASP), including lymphedema, were common among women with breast cancer in high-income countries before sentinel lymph node biopsy became the standard of care. Although ASP impair quality of life, as they affect daily life activities, their frequency and determinants in Sub-Saharan Africa remain unclear.MethodsAll women newly diagnosed with breast cancer at the Namibian, Ugandan, Nigerian, and Zambian sites of the African Breast Cancer-Disparities in Outcomes (ABC-DO) cohort study were included. At each 3-month follow-up interview, women answered the EORTC-QLQ-Br23 questionnaire, including three ASP items: shoulder/arm pain, arm stiffness, and arm/hand swelling. We estimated the cumulative incidence of first self-reported ASP, overall and stratified by study and treatment status, with deaths treated as competing events. To identify determinants of ASP, we estimated cause-specific hazard ratios using Cox models stratified by study site.ResultsAmong 1476 women, up to 4 years after diagnosis, 43% (95% CI 40–46), 36% (33–38) and 23% (20–25), respectively, self-reported having experienced arm/shoulder pain, stiffness and arm/hand swelling at least once. Although risks of self-reported ASP differed between sites, a more advanced breast cancer stage at diagnosis, having a lower socioeconomic position and receiving treatment increased the risk of reporting an ASP.ConclusionASP are very common in breast cancer survivors in Sub-Saharan Africa. They are influenced by different factors than those observed in high-income countries. There is a need to raise awareness and improve management of ASP within the African setting.

Geospatial barriers to healthcare access for breast cancer diagnosis in sub-Saharan African settings: The African Breast Cancer-Disparities in Outcomes Cohort Study.

We examined the geospatial dimension of delays to diagnosis of breast cancer in a prospective study of 1541 women newly diagnosed in the African Breast Cancer—Disparities in Outcomes (ABC‐DO) Study. Women were recruited at cancer treatment facilities in Namibia, Nigeria, Uganda and Zambia. The baseline interview included information used to generate the geospatial features: urban/rural residence, travel mode to treatment facility and straight‐line distances from home to first‐care provider and to diagnostic/treatment facility, categorized into country/ethnicity (population)‐specific quartiles. These factors were investigated in relation to delay in diagnosis (≥3 months since first symptom) and late stage at diagnosis (TNM: III, IV) using logistic regression, adjusted for population group and sociodemographic characteristics. The median (interquartile range) distances to first provider and diagnostic and treatment facilities were 5 (1‐37), 17 (3‐105) and 62 (5‐289) km, respectively. The majority had a delay in diagnosis (74%) and diagnosis at late stage (64%). Distance to first provider was not associated with delay in diagnosis or late stage at diagnosis. Rural residence was associated with delay, but the association did not persist after adjustment for sociodemographic characteristics. Distance to the diagnostic/treatment facility was associated with delay (highest vs lowest quartile: odds ratio (OR) = 1.56, 95% confidence interval (CI) = 1.08‐2.27) and late stage (overall: OR = 1.47, CI = 1.05‐2.06; without Nigerian hospitals where mostly local residents were treated: OR = 1.73, CI = 1.18‐2.54). These findings underscore the need for measures addressing the geospatial barriers to early diagnosis in sub‐Saharan African settings, including providing transport or travel allowance and decentralizing diagnostic services.

Preexisting morbidity profile of women newly diagnosed with breast cancer in sub-Saharan Africa: African Breast Cancer-Disparities in Outcomes study.

The presence of preexisting morbidities poses a challenge to cancer patient care. There is little information on the profile and prevalence of multi‐morbidities in breast cancer patients across middle income countries (MIC) to lower income countries (LIC) in sub‐Saharan Africa (SSA). The African Breast Cancer–Disparities in Outcomes (ABC‐DO) breast cancer cohort spans upper MICs South Africa and Namibia, lower MICs Zambia and Nigeria and LIC Uganda. At cancer diagnosis, seven morbidities were assessed: obesity, hypertension, diabetes, asthma/chronic obstructive pulmonary disease, heart disease, tuberculosis and HIV. Logistic regression models were used to assess determinants of morbidities and the influence of morbidities on advanced stage (stage III/IV) breast cancer diagnosis. Among 2189 women, morbidity prevalence was the highest for obesity (35%, country‐specific range 15‐57%), hypertension (32%, 15‐51%) and HIV (16%, 2‐26%) then for diabetes (7%, 4%‐10%), asthma (4%, 2%‐10%), tuberculosis (4%, 0%‐8%) and heart disease (3%, 1%‐7%). Obesity and hypertension were more common in upper MICs and in higher socioeconomic groups. Overall, 27% of women had at least two preexisting morbidities. Older women were more likely to have obesity (odds ratio: 1.09 per 10 years, 95% CI 1.01‐1.18), hypertension (1.98, 1.81‐2.17), diabetes (1.51, 1.32‐1.74) and heart disease (1.69, 1.37‐2.09) and were less likely to be HIV positive (0.64, 0.58‐0.71). Multi‐morbidity was not associated with stage at diagnosis, with the exception of earlier stage in obese and hypertensive women. Breast cancer patients in higher income countries and higher social groups in SSA face the additional burden of preexisting non‐communicable diseases, particularly obesity and hypertension, exacerbated by HIV in Southern/Eastern Africa.

Breast cancer survival and survival gap apportionment in sub-Saharan Africa (ABC-DO): a prospective cohort study

Breast cancer is the second leading cause of death from cancer in women in sub-Saharan Africa, yet there are few well characterised large-scale survival studies with complete follow-up data. We aimed to provide robust survival estimates in women in this setting and apportion the survival gaps. The African Breast Cancer-Disparities in Outcomes (ABC-DO) prospective cohort study was done at eight hospitals across five sub-Saharan African countries (Namibia, Nigeria, South Africa, Uganda, and Zambia). We prospectively recruited women (aged ≥18 years) who attended these hospitals with suspected breast cancer. Women were actively followed up by use of a telephone call once every 3 months, and a mobile health application was used to keep a dynamic record of follow-up calls due. We collected detailed sociodemographic, clinical, and treatment data. The primary outcome was 3-year overall survival, analysed by use of flexible proportional mortality models, and we predicted survival under scenarios of modified distributions of risk factors. Between Sept 8, 2014, and Dec 31, 2017, 2313 women were recruited from these eight hospitals, of whom 85 did not have breast cancer. Of the remaining 2228 women with breast cancer, 58 women with previous treatment or recurrence, and 14 women from small racial groups (white and Asian women in South Africa), were excluded. Of the 2156 women analysed, 1840 (85%) were histologically confirmed, 129 (6%) were cytologically confirmed, and 187 (9%) were clinically confirmed to have breast cancer. 2156 (97%) women were followed up for up to 3 years or up to Jan 1, 2019, whichever was earlier. Up to this date, 879 (41%) of these women had died, 1118 (52%) were alive, and 159 (7%) were censored early. 3-year overall survival was 50% (95% CI 48-53), but we observed variations in 3-year survival between different races in Namibia (from 90% in white women to 56% in Black women) and in South Africa (from 76% in mixed-race women to 59% in Black women), and between different countries (44-47% in Uganda and Zambia vs 36% in Nigeria). 215 (10%) of all women had died within 6 months of diagnosis, but 3-year overall survival remained low in women who survived to this timepoint (58%). Among survival determinants, improvements in early diagnosis and treatment were predicted to contribute to the largest increases in survival, with a combined absolute increase in survival of up to 22% in Nigeria, Zambia, and Uganda, when compared with the contributions of other factors (such as HIV or aggressive subtypes). Large variations in breast cancer survival in sub-Saharan African countries indicate that improvements are possible. At least a third of the projected 416 000 breast cancer deaths that will occur in this region in the next decade could be prevented through achievable downstaging and improvements in treatment. Improving survival in socially disadvantaged women warrants special attention. Susan G Komen and the International Agency for Research on Cancer.

Breast Cancer Survival and Survival Gap Apportionment in Sub-Saharan Africa: African Breast Cancer – Disparities in Outcomes ABC-DO Cohort

Background: Breast cancer is the second leading cause of cancer death in women in sub-Saharan Africa, yet there are few large-scale survival studies with rich clinical and epidemiologic data and few losses to follow-up to inform intervention strategies needed to avert premature deaths. Methods: In the hospital-based African Breast Cancer – Disparities in Outcomes (ABC-DO) cohort, characterized by rich sociodemographic, clinical and treatment data, 2214 women newly diagnosed with breast cancer across five Sub-Saharan African countries were prospectively followed using a trimonthly mobile phone contact protocol. Flexible proportional mortality models were used to estimate observed survival, hazard ratios and predict survival under scenarios of modifying risk factors. Findings: Among 2156 women followed up to three years, 879 (41%) died, 1118 (52%) were alive and 159 (7%) were censored early. Three-year survival was 50% overall, but varied between races in Namibia (90% white, 69% mixed-race and 56% in black women) and South Africa (76% mixed-race, 59% black) and between countries: 44 to 47% in Uganda and Zambia and 36% in Nigeria. Ten percent of all women died within 6 months of diagnosis, but three-year survival remained low (58%) conditional on surviving to this time-point. Among survival determinants, improvements in early diagnosis and treatment were predicted to result in the largest survival gains of up to a combined 22% absolute increase, compared to the contributions of social inequalities (up to 5%), non-receptor positive tumours (up to 4%) and young age or HIV (<2% each). Interpretation: Large variations in breast cancer survival in sub-Saharan African countries demonstrate that improvements are possible. At least one-third of the projected 416000 breast cancer deaths that will occur in this region in the next decade could be prevented through achievable down-staging and treatment improvements. Improving survival in socially disadvantaged women warrants special attention. Funding Statement: Susan G Komen Foundation and International Agency for Research on Cancer Declaration of Interests: The authors confirm no competing interests. Ethics Approval Statement: ABC-DO was approved by all institutional ethics committees and each woman provided informed consent.

African Breast Cancer—Disparities in Outcomes (ABC-DO) Study: preliminary survival analysis of the Zambian cohort

Objective: Breast cancer (BC) is often a death sentence for women in sub-Saharan Africa (SSA). Five-year survival estimates are near or below 50%, in contrast to almost 90% among U.S. women. The African Breast Cancer—Disparities in Outcomes (ABC-DO) study is a prospective hospital-based investigation of OS, quality of life (QOL), delays to diagnosis, and treatment of BC in SSA. We present survival estimates for the Zambian cohort.

Abstract C78: Pre-diagnostic journey of women with breast cancer and disparities in stage at diagnosis in Namibia: The African Breast Cancer–Disparities in Outcomes (ABC-DO) Cohort Study

Abstract Purpose: Breast cancer survival rates in sub-Saharan Africa (SSA) are low and the reasons therefor partly involve advanced disease at diagnosis. Within the African Breast Cancer – Disparities in Outcomes (ABC-DO) Study, a prospective study of breast cancer survival in multiple SSA settings, we examined spatiotemporal barriers to early presentation and diagnosis related to pre-diagnostic journey of women with breast cancer in the vast Southern African country of Namibia. Methods: 503 newly diagnosed breast cancer patients who presented at the Windhoek Central Hospital (WCH) in Namibia completed face-to-face interviews between September 2014 and October 2016. Participants were asked about sociodemographic factors, locations of residential home and health care providers, dates of visits to health care providers, and mode of transport. The straight-line distances from home to the first health care provider and the cancer care facility (WCH) were calculated. Clinical data including disease stage were extracted from medical records. Logistic regression models were used to estimate the odds ratios (OR) and corresponding 95% confidence intervals (CI) for late stage disease (stage III or IV) associated with the pre-diagnostic journey of women. Results: The analytical sample included 498 women, the majority of whom were black (79%), were diagnosed with a late-stage disease (stage III, 41%; stage IV, 15%), and resided outside Windhoek (within Namibia, 70%; outside Namibia, 10%). The mean age at diagnosis was 54 years (standard deviation, 14.7; range, 24–98). The distance from home to the WCH ranged from 0 to 1,643 km (median, 308 km). In unadjusted analyses, a longer distance from home to the WCH was associated with late stage (per 100 km increment: OR, 1.09; 95% CI, 1.04–1.15); however, distance to the first care provider was not statistically significantly associated with disease stage (OR per 100-km increment, 1.06; 95% CI, 0.97–1.17). Unadjusted analyses also showed that being black (vs. non-black: OR, 5.38. 95% CI, 3.30–8.78), longer time taken to travel to the WCH (OR per one-hour increment, 1.06; 95% CI, 1.02–1.10), and travelling by a transport service provided by a cancer association or a hospital (vs. travelling by private cars: OR, 2.71; 95% CI, 1.78–4.11) were associated with late stage whereas age, time interval between the first contact with a health care provider and the first visit to the WCH, and number of health care providers seen before referral to the WCH were not associated with disease stage. In the analysis that adjusted for race/ethnicity, neither travel distance/time from home to the WCH nor transport mode was statistically significantly associated with disease stage. Conclusions: In the Namibian subset of the ABC-DO Study, the association between a longer travel distance or time to the WCH and late stage of breast cancer at diagnosis appeared to be driven by the association between race/ethnicity and disease stage. The greater odds of late-stage diagnosis associated with the use of patient transport service likely reflect a response to urgent medical needs. The ongoing analysis will further investigate other potential barriers that explain disparities in stage at diagnosis among women in Namibia and other SSA settings. Citation Format: Kayo Togawa, Fiona McKenzie, Annelle Zietsman, Isabel dos Santos Silva, Valerie McCormack. Pre-diagnostic journey of women with breast cancer and disparities in stage at diagnosis in Namibia: The African Breast Cancer–Disparities in Outcomes (ABC-DO) Cohort Study [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr C78.

Drivers of advanced stage at breast cancer diagnosis in the multicountry African breast cancer – disparities in outcomes (ABC-DO) study

Drivers of advanced stage at breast cancer diagnosis in the multicountry African breast cancer – disparities in outcomes (ABC-DO) study

African Breast Cancer—Disparities in Outcomes (ABC-DO): protocol of a multicountry mobile health prospective study of breast cancer survival in sub-Saharan Africa

IntroductionSub-Saharan African (SSA) women with breast cancer (BC) have low survival rates from this potentially treatable disease. An understanding of context-specific societal, health-systems and woman-level barriers to BC early detection,...

African Breast Cancer—Disparities in Outcomes (ABC-DO): protocol of a multicountry mobile health prospective study of breast cancer survival in sub-Saharan Africa

African Breast Cancer—Disparities in Outcomes (ABC-DO): protocol of a multicountry mobile health prospective study of breast cancer survival in sub-Saharan Africa