In this PDAC lineage‐tracing system, EGFP+ cancer cells, upon the expression of Fsp1, irreversibly lose EGFP expression and initiate tdTomato expression, generating an EGFP‐to‐tdTomato fluorescence transition in cancer cells with Fsp1‐Cre‐captured EMT program. The gene discussed is S100A4; the disease is cancer.