The c-myc oncogene in tumor progression.

Tumor progression is a complex process involving many alternative molecular pathways that are often tissue and/or species specific. The c-myc oncogene has been implicated in malignant progression in a variety of human tumors. In many instances, amplification and/or elevated expression of the c-myc gene have been associated with poor prognosis or decreased survival; in other cases, correlations have been demonstrated between c-myc activation and specific parameters of advanced neoplastic stage such as hormone independence, transplantability, invasiveness, etc. The tumor types exhibiting c-myc as a "progressor" gene include breast, colon, small cell lung carcinoma, as well as ovarian cancer, lymphomas, and squamous cell carcinomas. The c-myc oncogene has been implicated in a number of experimental animal tumor models, especially rat liver. Several studies have found that c-myc often functions in rodent tumor progression. For example, rat skin carcinomas induced by ionizing radiation show c-myc amplification to be related directly to tumor size and age.