Since murine foregut tumor formation induced by oncogenic Ras/p53 expression is more frequently found in the region adjacent to the SCJ within the forestomach tissues (Fig. 1), we investigated whether the Krt15-CrePR transgene27 could selectively label progenitor cells within the forestomach (squamous epithelia), but not cells within the hindstomach tissues (glandular epithelia). The gene discussed is TP53; the disease is neoplasm.