When transfecting a lineage tracing episomal library (LTv-BC-H2B-GFP episome library) of ~1.2 × 106 unique barcodes in a clonal isogenic cancer cell model (HA1ER cells, F12 clone, Supplementary Fig. 1a, b), we retrieved ~1.7–2 × 105 different barcodes per 10 M reads sequenced at time 0, followed by ~0.9–1.2 × 105 and ~0.8–1 × 105 upon 5 and 15 days of tracing, respectively (Fig. 1c). The gene discussed is H2BC21; the disease is breast cancer.