This document discusses cancer and its causes at a cellular level. It describes how cancer develops from normal cells transforming into abnormal cells that destroy normal tissue. Cancer results from oncogene activation and anti-oncogene diminishment due to mutations from environmental factors like radiation, chemicals, viruses, and lifestyle factors. Oncogenes are genes that cause cell transformation, often originating from viruses. They can become activated through mutations that alter gene expression or protein function. Tumor suppressor genes normally inhibit cell growth but are deactivated in cancer. The document also outlines several tumor markers - abnormally produced molecules - that can indicate certain cancer types.