Breast cancer (BC) in women has the highest global age-standardized incidence rate (ASR) per 100,000 persons per year and is the most common cause of death due to cancer worldwide,¹ including in Saudi Arabia (SA).² Although the ASR in the Saudi Kingdom is far less than the global figure (27.7 vs 89.9 per 100,000 persons per year, respectively),³ over the past three decades, a sharp rise in local cancer incidence and mortality has been reported,^4,5 which is in concordance with the global transition cancer theory and changes in risk factors.⁶ Obesity (body mass index [BMI] ≥30 kg/m²) is a major global health problem, especially in wealthy or transitional economies. Between 1980 and 2015, its prevalence doubled in >70 countries, and the numbers continue to increase in most other nations,⁷ thereby affecting 20–41% of the populations.⁸ Among Saudi women, the prevalence of obesity has significantly increased over the past several decades (14.3% in 1975, 30% in 2001, and 41.2% in 2016),⁹ and in conjunction with being overweight (BMI ≥25 kg/m²), the prevalence is approximately 70%.⁹ Excess body weight is associated with increased cancer incidence, and poor overall and BC-specific survival.^10,11 The disease characteristics of obesity include larger tumors, more positive nodes, higher tumor grades, more triple-negative disease in premenopausal women, and more hormone-positive tumors in postmenopausal women.^12–15 Ethnicity is associated with variations in age and tumor stage at diagnosis. Moreover, race, age, menopausal status, and BMI at diagnosis are associated with variations in the molecular subtype distribution.^16–21

We observed a high rate of obesity and a high rate of adverse clinical features of non-metastatic BC at diagnosis in Saudi women. However, there are no data on BMI prevalence or the impact of BMI on BC. This study aimed to evaluate the BMI impact on non-metastatic BC among Saudi women and evaluate the associated factors with advanced clinical stage.