Introduction: Immediate breast reconstruction (IBR) is an established component of comprehensive breast cancer (BC) care and is publicly funded in Canada. In Ontario, Canada’s most populous province, system-level efforts to increase access to IBR- including updated provincial clinical guidelines and reorganization of BC care pathways- have been implemented over the past decade. However, whether these structural supports have been successful and translate into equitable IBR access remains unclear and has not been re-evaluated. The objective of this study was to explore contemporary temporal trends and variation in IBR access by social and geographic factors in Ontario, Canada.
Methods: A population-based cohort study was conducted using linked administrative datasets of patients who underwent mastectomy for BC with and without IBR between January 2018-July 2023. Multivariable logistic regression assessed associations between receipt of IBR and individual-level demographic and clinical characteristics (age, immigration status, comorbidities, neoadjuvant chemotherapy), neighbourhood-level material deprivation, and Ontario Health geographic planning regions. 
Results: Among 21,933 BC patients who underwent a mastectomy, 26.3% (n=5,758) received IBR. The proportion of IBR increased from 20.9% in 2018 to 30.0% by mid-2023, with a steady 17% increase in adjusted odds per year (aOR 1.17, 95% CI 1.14-1.19). Patients residing in Toronto, the most populous urban city, were more likely to receive IBR than those in all other regions, with the lowest adjusted odds observed in the northernmost region (aOR 0.22, 95% CI 0.18–0.28). Patients residing in the least materially deprived neighbourhoods had more than twice the adjusted odds of receiving IBR compared with those residing in the most deprived neighbourhoods (aOR 2.07, 95% CI 1.85–2.31). Immigrants were also less likely to receive IBR compared to non-immigrants (aOR 0.70, 95% CI 0.65-0.77).
Conclusions: Although utilization of IBR has increased over time within a universal healthcare system, marked social and geographic variation persisted after adjustment for clinical factors. The alignment of this variation by region, neighbourhood material deprivation, and immigration status suggests that structural supports and increased uptake at the population-level alone are insufficient to achieve equitable IBR access, even within a single public payer universal healthcare system. Engagement with equity-deserving patients and communities is needed to better understand perceived and realized barriers to accessing IBR, and to inform the development and implementation of equity-orientated health system strategies for reconstructive BC care.