ABSTRACT
Cancer (the uncontrolled growth and spread of unwanted cells) is a disease in which abnormal cells grow in an uncontrolled manner and spread to a nearby region. The major types of cancer are carcinoma, sarcoma, melanoma, lymphoma, leukemia, and central nervous system cancers. Cancer stem cell theory is gaining popularity among biologists toward cancer research. The tumor microenvironment can be divided into the chemical microenvironment and the cellular microenvironment. Induction of cancer by genetic mutations, which occur due to chemical and radiation exposure, abnormality in metabolism, etc., is referred to as carcinogenesis. Genes involved in the process of carcinogenesis are broadly classified into three. They are oncogenes (cell accelerators), tumor suppressor genes (cell decelerator), and DNA repair genes. The three major steps in carcinogenesis are: malignant transformation, invasion, and metastasis. It is well known that the metastasis (cancer cell spread or dissemination) is the cause of most of the cancer deaths.
