Methylnitrosourea induction of thymomas in AKR mice requires one or two "hits" only.

Induction of thymomas by methylnitrosourea in many strains of mice requires 3 "hits". AKR mice develop thymomas spontaneously late in life, probably because of their large load of viral leukemia oncogenes. It was expected therefore, and so found, that methylnitrosourea induces thymomas in AKR mice with only 1 or 2 "hits". The viral oncogene therefore appears to function as a dominant "hit" gene cooperating with the chemical carcinogen.