["British Journal of Learning Disabilities, Volume 54, Issue 1, Page 3-14, March 2026. ", "\nABSTRACT\n\nBackground\nAdult females with intellectual or developmental disabilities are more likely to die following a breast cancer diagnosis. Differences in access to cancer treatment may contribute to these survival differences. We explored how one woman with intellectual or developmental disabilities received guideline‐recommended breast cancer treatment.\n\n\nMethods\nA critical realist case study was used. The single case included a woman with intellectual or developmental disabilities previously diagnosed with breast cancer (pseudonym: Sandra), her support worker, and her surgeon. We conducted four semi‐structured interviews with (1) Sandra and her support worker, (2) her support worker, (3) her surgeon and (4) her sister. Data were analyzed using critical realist thematic analysis. Neurodiverse advisors assisted with developing easy‐read and accessible study materials.\n\n\nFindings\nSandra had stage II breast cancer and received guideline‐recommended breast cancer treatment. Four themes were identified that influenced her breast cancer treatment: attitudes, relationships, shared decision‐making and accessible accommodations, and advocacy.\n\n\nConclusions\nThis case study provides a positive example of the type of care adult females with intellectual or developmental disabilities diagnosed with breast cancer can receive and could inform strategies for improving gaps in care including the involvement of patient navigators trained in working with this patient group.\n"]