Background: Informal caregivers are essential partners in the delivery of cancer care, and often can accurately identify and report symptoms and physical function of the patients they care for. We assessed whether such reporting by caregivers is predictive of adverse patient outcomes. Methods: In this prospective study, adult solid cancer patients on active intravenous systemic therapies and their informal caregivers were recruited from 18 Kaiser Permanente Northern California cancer centers. Using a study mobile app (TOGETHERCare), caregivers completed weekly surveys for 4 weeks, which were based on normalized NIH-PROMIS scores to report patients’ physical function and PRO-CTCAE to report patients’ symptoms. Patients’ adverse clinical outcomes were abstracted from the medical record and included: emergency department (ED) visits or hospitalizations, grade 3-4 adverse events (AEs), and treatment delays, up to 1 month following the 4-week study period, as well as mortality and hospice referrals up to 6 months following the study period. Simple univariate logistic regressions were used to correlate caregiver reports (either at baseline or most proximal preceding an adverse outcome) with mortality and hospice referrals, and quasi-Poisson regressions were used for the other adverse outcome measures. Results: Fifty-four patient-caregiver dyads were enrolled, and 52 were included in this analysis. A third of patients had breast cancer and almost 75% had stage 3 or 4 disease. Caregivers predominantly identified as male (61.5%), spouse/partner (76.9%), and non-Hispanic White (63.5%). At least one adverse outcome was experienced by 36.5% of the patients. Caregiver-reported PRO-CTCAE consistently predicted ED/hospitalizations and mortality, and caregiver-reported PROMIS scores predicted hospice referrals (see Table). Conclusions: The results suggest that caregiver reporting of patients’ symptoms and physical function could help provide early predictions of adverse patient outcomes.