ImportanceOral anticancer drugs (OACDs) are increasingly prescribed for cancer treatment and require significant coordination of care. Retrospective studies suggest that 10% to 20% of OACD prescriptions are never received by the patients, but the reasons behind this are poorly understood.ObjectivesTo estimate the rate of failure to receive OACD prescriptions among patients with cancer and to examine the underlying reasons for this failure.Design, Setting, and ParticipantsA prospective cohort study was conducted among patients with cancer who were prescribed a new OACD from January 1, 2018, to December 31, 2019, at an urban academic medical center. Data analysis was conducted between 2021 and 2022.Main Outcomes and MeasuresPatient demographic, clinical, and insurance data and OACD delivery dates were collected. The reasons for a failure to receive a prescribed OACD within 3 months were confirmed by manual review of medical records and were classified into 7 categories: clinical deterioration, financial access, clinician-directed change in decision-making, patient-directed change in decision-making, transfer of care, loss to follow-up, and unknown or other. A multivariable random-effects model was developed to identify factors associated with failure to receive a prescribed OACD.ResultsThe cohort included 1024 patients (538 men [53%]; mean [SD] age, 66.2 [13.9] years; 463 non-Hispanic White patients [45%], 140 non-Hispanic Black patients [14%], and 300 Hispanic patients [29%]), representing 1197 new OACD prescriptions. Of the 1197 prescriptions, 158 (13%) were categorized as having not been received by the patient. The most common reason for the failure to receive a prescribed OACD was due to patient and clinician decision-making (73 of 158 [46%]), and 20 cases (13%) in which prescriptions were not received were associated with financial access issues. In multivariable analysis, patients with a nonmetastatic solid malignant neoplasm were significantly less likely to not receive their OACDs than those with a hematologic malignant neoplasm (odds ratio, 0.57 [95% CI, 0.33-1.00]; P = .048).Conclusions and RelevanceThis cohort study of patients prescribed a new OACD found that 13% of prescriptions were not received. The failure to receive a prescribed OACD was most frequently due to a change in clinical decision-making or patient choice. Ultimately, the reasons for the failure to receive a prescribed OACD were multifactorial and may have been appropriate in some cases.