In order to trace the lineage of the MMTV-PyMT tumor cells, either Krt8 (luminal) or Krt5 (basal) specific, tamoxifen-inducible CreERT promoters [13] were used to induce expression of GFP in an mTmG reporter mouse [33] to label luminal or basal cells, respectively (Fig. 4A, B). The gene discussed is KRT5; the disease is neoplasm.