Glycated haemoglobin and breast cancer among women evaluated for breast masses in Meru County, Kenya: A hospital-based case-control study

Introduction: The dual burden of type 2 diabetes mellitus (T2DM) and breast cancer is rising in low- and middle-income countries, including Kenya. Chronic hyperglycemia and the low-grade inflammation that accompanies it may link the two conditions. We examined the association between glycated haemoglobin (HbA1c) and breast cancer among women evaluated for breast masses at a Kenyan referral hospital. Methods: This hospital-based case-control study at Meru Teaching and Referral Hospital enrolled 285 women: 143 with histologically confirmed breast cancer and 142 age-matched controls with benign breast masses from the same referral pathway. Data on hormonal, hereditary and lifestyle factors were collected by structured questionnaire; body mass index (BMI) and HbA1c were measured at enrolment. Multivariable logistic regression estimated adjusted odds ratios (aORs), with HbA1c and previously diagnosed T2DM modelled separately to avoid over-adjustment. Collinearity diagnostics, a sensitivity analysis excluding women with diagnosed T2DM, and receiver operating characteristic (ROC) analysis were performed. Results: HbA1c >6.5% was present in 65.7% (94/143) of cases and 15.5% (22/142) of controls (OR = 10.46; 95% CI: 5.91–18.52). Each 1-percentage-point increase in HbA1c was associated with higher odds of breast cancer after adjustment for BMI, family history, alcohol consumption, hormonal contraceptive use, education and marital status (aOR = 9.30; 95% CI: 5.14–16.83), including among women without diagnosed T2DM (aOR = 6.52; 95% CI: 3.36–12.65). Previously diagnosed T2DM (aOR = 5.62; 95% CI: 2.80–11.27), alcohol consumption (aOR = 4.04; 1.71–9.57), family history (aOR = 2.74; 1.34–5.59), hormonal contraceptive use (aOR = 2.15; 1.14–4.06) and BMI (aOR = 1.39 per kg/m²; 1.27–1.52) were also associated with breast cancer. No multicollinearity was detected (all VIFs ≤1.13). At the 6.5% cut-point, HbA1c showed moderate discrimination (AUC = 0.751; sensitivity 65.7%; specificity 84.5%). Conclusion: Elevated HbA1c was strongly associated with breast cancer in this Kenyan referral setting. Because HbA1c was measured at diagnosis, temporality cannot be inferred, and its moderate discriminatory ability does not support its use for breast cancer screening. Routine assessment and management of glycemic status among women diagnosed with breast cancer is warranted, and prospective studies are needed.