Wiktionary
n. (context genetics English) A gene, that promotes the specialization and division of normal cells, that becomes an oncogene following mutation
WordNet
n. a normal gene that has the potential to become an oncogene
Usage examples of "proto-oncogene".
It's an appropriate name, because the DNA in cancer cells is different from the stuff in normal body cells, in that the harmless proto-oncogenes have been transformed into new, malignant oncogenes.
Colette went ahead with therapy to repair Jack's documented genetic defects, the ones that were guaranteed to be harmful, knowing that there was an off chance that the proto-oncogenes might be triggered.
Jack was often in considerable pain, although he never let it daunt him, and he steadfastly maintained that pain, like the paradoxical proto-oncogenes, would not have evolved in us and remained a part of the higher animal condition for so long unless it had more than a fleeting, avoidance-factor/signal-factor value.