HRAS and neoplasm: Following orthotopic injection of the Ctl and PARGwt HMLE-derived cell lines into the mammary fat pad of NOD/SCID mice, we observed tumor growth only in the PARGwt group (Fig. 2d–f), albeit with an extended latency of approximately 70 days (data not shown), consistent with the low penetrance and long latency observed in HMLE cells expressing other oncogenes including mutant H-Ras [28].