There are somatic mutations (vs. germ line, which would be inherited). Somatic mutations are just errors in genome duplication in somatic cell lines - i.e. not

There are somatic mutations (vs. germ line, which would be inherited). Somatic mutations are just errors in genome duplication in somatic cell lines - i.e. not germ line. These accumulate over time and, yes, can be oncogenic. Many others simply have no consequence at all. For many organisms, the germ line is 'sequestered' fairly early in development, in part to limit the number of replications needed, and thus errors that accumulate.