Prevalence Of Preexisting Mental Illness In Seer-Medicare Breast Cancer Patients.

e13564Background: Patients with mental illness (MI) existing before breast cancer (BC) may face varying diagnostic and treatment practices. However, studies have not explored the full range of preexisting MI. We described MI prevalence prior to BC diagnosis, and examined the impact of lookback period on reported MI prevalence in a broad national sample of patients from the SEER-Medicare linked cancer registry. Optimizing lookback improves the balance of sample size to misclassification risk. Methods: Included women were part of a study about preexisting MI and influence on endocrine therapy use, aged 68+ at their first BC diagnosed 2007-2013, excluding lobular carcinoma in situ. All patients had continuous Medicare parts A and B for 36+ months prior and 18+ months after BC diagnosis, 3+ months of continuous part D coverage prior and 18+ months after, and a record of surgery. MI was identified with one inpatient or two outpatient ICD-9 diagnoses occurring 30+ days apart. Results: Estimates of any MI preval...