Determinants of Early-Stage Breast Cancer Presentation in Western Kazakhstan: A Population-Based Analysis of Urban–Rural Disparities and Diagnostic Pathways (2015–2025)

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Abstract
Background and Objectives: Breast cancer is the leading oncological diagnosis among women in Kazakhstan, yet a substantial proportion of cases are still detected beyond the earliest stages, particularly in peripheral regions such as Aktobe. Despite a national mammography screening programme covering women aged 40–70 years since 2018, structural differences in access to early diagnosis—related to geography, socioeconomic circumstances, and the diagnostic pathway—may compromise outcomes. We aimed to identify factors independently associated with early-stage presentation and to characterise the temporal pattern of early-stage presentation without assuming a monotonic trend. Methods and Materials: We conducted a retrospective, population-based analytical study of all confirmed breast cancer cases (ICD-10 C50) registered in the Aktobe regional cancer registry and diagnosed between 1 January 2015 and 31 December 2025 (n = 2232). The outcome was early-stage presentation, defined literally as Stages I–IIa at diagnosis, with Stages IIb–IV as the comparator; this is a stage-at-presentation classification and is not intended to indicate surgical operability or treatment sequence. Multivariable logistic regression estimated adjusted odds ratios (aORs). Two models were used: Model A included age, sex, residence, administrative nationality, employment/social status, and calendar year; Model B additionally included the diagnostic pathway, which may lie on the causal pathway between structural determinants and stage. Calendar year was modelled as a categorical variable, and a complementary phase-based model (2015–2017, 2018–2019, 2020–2022, 2023–2025) was fitted. A residence-by-year interaction; a multinomial sensitivity analysis separating Stages IIb, III, and IV; discrimination (AUC, Brier score); and calibration (Hosmer–Lemeshow test, calibration plot) were also assessed. Results: Of 2232 patients (99.1% female; mean age 57.0 ± 12.5 years), 1323 (59.3%) presented at Stages I–IIa. In Model A, rural residence (aOR 0.77, 95% CI 0.64–0.93; p = 0.006), unemployment relative to employment (aOR 0.69, 95% CI 0.52–0.90; p = 0.007), Russian administrative nationality (aOR 0.64, 95% CI 0.50–0.82; p < 0.001), and other non-Kazakh nationalities (aOR 0.73, 95% CI 0.58–0.94; p = 0.012) were independently associated with lower odds of Stage I–IIa presentation. In Model B, patient-initiated (self-referral) presentation was associated with lower odds relative to clinical examination room detection (aOR 0.46, 95% CI 0.30–0.72; p < 0.001), whereas organised screening was not significantly associated (aOR 1.52, 95% CI 0.95–2.43; p = 0.082). The calendar-year pattern was clearly non-linear (categorical vs. linear year: likelihood-ratio χ2 = 76.1, df = 9, p < 0.001): odds of Stage I–IIa presentation peaked in 2018 (aOR 2.49, 95% CI 1.57–3.93 vs. 2015), were lowest in 2022 (aOR 0.64, 95% CI 0.42–0.97), and partially recovered thereafter. In the phase-based model (reference 2015–2017), the aORs were 1.62 (95% CI 1.22–2.15) for 2018–2019, 0.54 (95% CI 0.41–0.69) for 2020–2022, and 0.62 (95% CI 0.46–0.84) for 2023–2025. Model discrimination was limited (AUC 0.648, 95% CI 0.625–0.671; Brier score 0.226) with acceptable calibration (Hosmer–Lemeshow χ2 = 8.38, df = 8, p = 0.40). Conclusions: In this registry-based cohort, rural residence, unemployment, non-Kazakh administrative nationality, and patient-initiated presentation were independently associated with lower odds of early-stage breast cancer presentation. The temporal pattern was non-monotonic, with the highest odds around the 2018 screening expansion, a marked reduction during 2020–2022, and only partial recovery thereafter. These are observational associations rather than causal or programme-evaluation findings; they should be interpreted as hypothesis-generating and require confirmation with screening-process, service-capacity, and patient-level access data.

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