Cancer Biology Fundamentals

Cancer results from uncontrolled cell proliferation caused by accumulated mutations in genes regulating cell growth, differentiation, and apoptosis. A normal cell can pause, repair damage, enter a resting state, or die; a malignant cell progressively loses those restraints and passes its abnormal behaviour to its descendants. The cell cycle consists of G1, when the cell grows and prepares for DNA synthesis; S phase, when DNA is replicated; G2, when the cell checks its preparation for division; and M phase, when mitosis and cytokinesis occur. G0 is a relatively quiescent state. Control points normally prevent a cell with serious DNA damage from progressing through this sequence. Proto-oncogenes normally promote appropriate growth and survival. When activated or amplified, they become oncogenes and send growth signals when the cell should be resting. Tumour-suppressor genes normally slow proliferation, repair DNA, or trigger apoptosis; their inactivation removes those brakes. Cancer usually reflects several cooperating changes rather than one isolated mutation, allowing a clone to survive, expand, recruit blood supply, invade tissue, and sometimes spread through lymphatic or blood vessels. This biology explains why treatment can...