Using a Tg(mitfa:BRAFV600E); p53(lf); Tg(crestin:EGFP) strain that marks tumor initiating cells, we identified zebrafish with early tumors (<20 cells), dissected these tumors and performed flow cytometry to determine DNA content of crestin:EGFP-positive tumor cells. The gene discussed is TP53; the disease is neoplasm.