Human
colorectal cancers often possess multiple mutations, including three to six driver mutations per
tumor. The timing of when these mutations occur during
tumor development and progression continues to be debated. More advanced lesions carry a greater number of driver mutations, indicating that colon
tumors might progress from
adenomas to
carcinomas through the stepwise accumulation of mutations following
tumor initiation. However, mutations that have been implicated in
tumor progression have been identified in normal-appearing epithelial cells of the colon, leaving the possibility that these mutations might be present before the initiation of
tumorigenesis. We utilized mouse models of
colon cancer to investigate whether
tumorigenesis still occurs through the
adenoma-to-
carcinoma sequence when multiple mutations are present at the time of
tumor initiation. To create a model in which
tumors could concomitantly possess mutations in Apc, Kras, and Pik3ca, we developed a novel minimally invasive technique to administer an adenovirus expressing
Cre recombinase to a focal region of the colon. Here, we demonstrate that the presence of these additional driver mutations at the time of
tumor initiation results in increased
tumor multiplicity and an increased rate of progression to invasive
adenocarcinomas. These
cancers can even metastasize to retroperitoneal lymph nodes or the liver. However, despite having as many as three concomitant driver mutations at the time of initiation, these
tumors still proceed through the
adenoma-to-
carcinoma sequence.