Table 7.2.

Cell-Transforming Retroviruses

Virus Type	Time to Tumor Formation	Efficiency of Tumor Formation	Type of Oncogene
Transducing (acutely transforming)	Short (e.g., weeks)	High (up to 100%)	c-onc transduced by virus (i.e., v-onc present in virus genome; usually replication defective)
cis-Activating (chronic transforming)	Intermediate (e.g., months)	Intermediate	c-onc in cell genome activated by provirus insertion; no oncogene present in virus genome (replication competent)
trans-Activating	Long (e.g., years)	Low (<1%)	Activation of cellular genes by trans-acting virus proteins (replication competent)