Abstract Body (Do not enter title and authors here): Background: Anthracyclines are highly effective, yet cancer therapy-related cardiac dysfunction (CTRCD) and heart failure are known adverse effects. Elevations in hsTnT and NT-proBNP may predict CTRCD but the optimal timing of testing is not defined. Research question: What are the longitudinal cardiac biomarker trends with anthracycline treatment and do biomarker values differ pre and post anthracycline infusion? Methods: Participants 18+ with planned treatment with doxorubicin for breast cancer or lymphoma were enrolled in a prospective cohort study at 3 hospitals in a single health system. Biomarkers including hsTnT (normal <12 ng/L) and NT-proBNP (normal 0-125 pg/mL) were collected prior to and immediately after each anthracycline infusion and every 6 months for 24 months. Echocardiograms were conducted prior to doxorubicin treatment in all participants and 6-12 months after doxorubicin in the majority. Patients were followed for 24 months. Baseline cardiovascular risk was determined using the Heart Failure Association-International Cardio-Oncology Society (HFA-ICOS) algorithm. Change in biomarkers over time was analyzed using generalized estimating equations and the linear mixed effect model. Results: We enrolled 43 participants (mean age 50, 51% female) with lymphoma (n=33) or breast cancer (n=10). The baseline mean hsTnT was 9 (SD 18) and NT-proBNP 384 (SD 741). HFA-ICOS risk was low in 21 (49%), moderate in 11 (26%), high in 9 (21%) and very high risk in 2 (4%) Pre-anthracycline infusion hsTnT level trends increased significantly with each cycle while patients were on chemotherapy and trended downwards after completion of chemotherapy (p<0.001) (Fig. A). NT-proBNP did not change (p=NS) (Fig. B). Among the 36 participants with pre and post anthracycline infusion biomarkers, there was a decrease in post-infusion hsTnT levels (p=0.018) and no difference in pre and post NT-proBNP (p=0.10). Of the 32 patients with follow-up echocardiograms, 2 patients developed moderate asymptomatic and 2 developed moderate symptomatic CTRCD. Higher peak troponin level was associated with CTRCD (p=0.051). Conclusions: In this small study, there was a broad representation of cardiovascular risk among breast cancer and lymphoma patients. HsTnT, but not NT-proBNP, significantly increased with anthracycline chemotherapy. Peak troponin was associated with CTRCD. Further studies with larger sample size are needed to assess the effect of changes in biomarkers on CTRCD.