ApcMin/+ mice, Ptch1+/− mice and Tsc2+/− Eker rats are special animal models of carcinogenesis owing to a heterozygous germline mutation of a cancer driver gene, and thus it must be considered whether LOH and copy number variations that are a consequence of chromosomal structural instability caused by the absence of one allele can be a general mechanism. The gene discussed is PTCH1; the disease is cancer.