In sporadic cases of retinoblastoma, only two gene mutations are thought to be necessary in the same cell for a tumor to develop. this happens when an organism inherits a mutant allele and a wild-type allele forms the parents. when the wild-type allele is mutated, resulting in tumorigenesis, this process is called, . metastasizingb. attenuationc. gain of heterozygosityd. loss of heterozygositye. recombination