Since it remained unclear whether basal or luminal cells, or both, represent the cell types originating prostate tumors in the context of PTEN deletion, Wang and coworkers used a novel cell-tracing strategy to assess tumor cell origin in a variety of mouse prostate cancer models, including PTEN+/-, Hi-Myc, NKX 3.1, and TRAMP mice [542]. The gene discussed is PTEN; the disease is prostate carcinoma.