 However, if the insertion occurs in an essential gene or a gene that is involved in cellular replication or programmed cell death, the insertion may compromise the viability of the cell or even cause the cell to replicate interminably – leading to the formation of a tumor, which may become cancerous.Insertional mutagenesis is possible whether the virus is of the self-inactivating types commonly used in gene therapy or competent to replicate.The virus inserts a gene (known as a viral oncogene) normally near the cellular myc (c-myc)gene.