Strikingly, p190B+/-Neu mice developed tumors with a markedly increased latency compared with the MMTV-Neu mice (74 weeks vs. 35 weeks, P < 0.0001; Figure 1a), In addition, p190B haploinsufficiency significantly reduced tumor penetrance, in that 53% (8/15) of the heterozygous mice had palpable tumors as compared with 100% (20/20) of the MMTV-Neu wild-type mice (P < 0.001). Here, ARHGAP5 is linked to neoplasm.