PROJECT SUMMARY/ABSTRACT After a cancer diagnosis, the potential for overlap in opioid and benzodiazepine prescriptions is substantial, with up to 30% of patients concurrently prescribed both types of drugs. Opioids continue to be the mainstay of cancer-related pain management, and benzodiazepines are frequently prescribed to help patients manage other common symptoms of cancer and its treatment. When prescribed in combination, opioids and benzodiazepines can have the unintended consequence of compromising patient safety and well-being— particularly for older patients. Among older members of the general population, co-prescribing of opioids with benzodiazepines has been linked to a substantially increased risk of injurious falls, fractures, and opioid overdose events. The risks of opioid and benzodiazepine co-prescribing may be compounded in older adults with cancer, who are more vulnerable to the effects of opioids and benzodiazepines on postural stability and cognition due to the neurological effects of chemotherapy. In addition, older adults with cancer frequently experience breathing difficulties (i.e., dyspnea), which can further predispose them to opioid- and benzodiazepine-related respiratory depression—the cause of overdose death. At present, there are critical knowledge gaps that hinder efforts in the older adult population to (1) reduce avoidable co-prescribing of opioids and benzodiazepines after a cancer diagnosis and (2) prevent harms among those who are exposed to this drug combination after a cancer diagnosis. First, we lack fundamental knowledge about population-level patterns of opioid and benzodiazepine co-prescribing among older adults with cancer. Second, no studies have examined the burden of harms resulting from co-prescribing among members of this population. Third, no studies have explored providers’ perspectives with respect to opioid and benzodiazepine co-prescribing among older patients with cancer. Our proposed study uses an explanatory sequential mixed-methods design to address these evidence gaps. The quantitative phase of our study will use SEER-Medicare data to (a) Characterize patterns of opioid and benzodiazepine co-prescribing among older adults diagnosed with breast, colorectal, or lung cancer (Aim 1) and (b) Examine the risks of avoidable harms associated with opioid and benzodiazepine co-prescribing among members of this population (Aim 2). In the qualitative phase of the study, we will conduct semi-structured interviews with providers to identify factors that influence their practices with respect to co-prescribing and mitigating associated risks among older adults with cancer (Aim 3). At the conclusion of this study, we will have a contextually rich understanding of the extent of co-prescribing and harms potentially resulting from co-prescribing among older adults with cancer, and factors that may facilitate or hinder efforts to reduce unnecessary co-prescribing and improve the use of risk mitigation strate...