Despite achieving high rates of complete remission with RCHOP immuno-chemotherapy, almost all patients with follicular lymphoma (FL) will experience multiple relapses after treatment. The lack of experimental model of FL limits our understanding of heterogeneity in treatment response. Here we characterized a new model of FL patient-derived xenograft (PDX) in avian embryos. Based on 20 biopsies, we observed that tumor volume reduction upon RCHOP treatment in ovo predicted progression free survival in multivariate analysis. To further explore the model, we performed single-cell RNA sequencing and discovered a signature of 21 genes upregulated after RCHOP exposure, with significant intratumoral heterogeneity. Among these genes, we functionally validated BAX as a critical effector of RCHOP which can be targeted with venetoclax in vitro and in ovo. Overall, the FL-AVI-PDX model is a platform for functional precision oncology in FL, which captures both interpatient and intratumoral heterogeneity, and opens an avenue for drug development.