["Journal of Intellectual Disability Research, Volume 70, Issue 5, Page 500-517, May 2026. ", "\nABSTRACT\n\nBackground\nPeople with intellectual or developmental disabilities (IDD) experience breast cancer care inequities relative to those without IDD. Identifying factors associated with receipt of breast cancer treatment among those with IDD is needed to provide guidance and inform resources for improving patient‐centred care. This study explores factors associated with receipt of breast cancer treatment among individuals with IDD.\n\n\nMethods\nWe conducted a population‐based retrospective cohort study with administrative health data in Ontario, Canada. Adults with IDD diagnosed with Stage I–III female breast cancer between 2007 and 2018 were included. We examined factors associated with receipt of breast cancer treatment based on stage‐specific guideline recommendations. Sociodemographic (e.g., age, region, and rurality), clinical (e.g., comorbidities), cancer‐related (e.g., stage at diagnosis and nodal status) and health system (e.g., family interview with a physician) factors associated with overall treatment, surgical resection, mastectomy and radiation were explored using modified Poisson regression with robust standard error variance. Crude and adjusted risk ratios with 95% confidence intervals were estimated.\n\n\nResults\nThe overall treatment cohort, surgical resection cohort, mastectomy cohort and radiation cohort included 365, 365, 333 and 138 females with IDD, respectively. Age, stage at diagnosis and lymph node status were significantly associated with overall breast cancer treatment. We identified that age, grade, lymph node status and radiation consult were significantly associated with surgical resection receipt. Among individuals who received surgery, those who were older, who had more advanced stages at diagnosis or who had a family interview were more likely to have mastectomy rather than breast‐conserving surgery. Age and lymph node status were significantly associated with receipt of radiation.\n\n\nConclusions\nSociodemographic, clinical, cancer‐related and health system factors were associated with receipt of breast cancer treatment in a sample of breast cancer patients with IDD. Overall, these findings suggest that health system factors could contribute to disparities in treatment among individuals with IDD diagnosed with breast cancer.\n\n"]