Oncogenes are mutated and/or overexpressed at high levels in tumor cells. Tumors of the lung, breast, pancreas, and colon may display specific oncogenetic features. These tumors have been largely associated with exposure to environmental carcinogens and a variety of biological agents, including viruses. These carcinogens can induce specific genetic and epigenetic alterations in these tissues, leading to aberrant functioning of oncogenes and tumor suppressor genes. On the microRNAs (miRNAs) there are significant modifiers of both transcription and translation of oncogenes in carcinogenesis. In the last 50 years, several oncogenes and microRNAs related to these oncogenes have been identified in different types of human cancers. It is now clear that high expression of oncogenes, DNA damage response, and regulation of the cell cycle are related to the circadian clock. This book will mainly focus on the expressions of different oncogenes in breast, colon, and lung cancers. Moreover, readers will gain qualified scientific knowledge of the alterations in miRNAs in different types of cancers and the effects of the circadian clock on the expression of oncogenes in carcinogenesis.