Cells divide to grow tissue and to replace worn-out or damaged cells. The cell cycle is tightly controlled, and cancer begins when that control breaks down.
Phases
In interphase the cell grows (G1), copies its DNA (S) and prepares to divide (G2). In mitosis (M) the copied chromosomes are split evenly into two daughter cells.
Checkpoints
At key points the cell checks for DNA damage before it moves on. Proteins such as p53 can stop the cycle to allow repair or trigger planned cell death (apoptosis).
Oncogenes and tumor suppressors
Oncogenes act like a stuck accelerator that pushes cells to divide, and tumor suppressor genes act as the brakes. Cancer usually needs several mutations that both press the accelerator and remove the brakes.
Benign and malignant
Benign tumors grow slowly and stay in place. Malignant tumors invade nearby tissue and can spread through blood or lymph to distant sites (metastasis).
Risk and treatment
Tobacco, UV light, some viruses and aging raise the number of mutations. Many chemotherapy drugs and radiation target fast-dividing cells, which is why they also affect hair, the gut lining and the bone marrow.
At the bedside
Teach patients warning signs such as a changing mole, a new lump or unexplained weight loss. During chemotherapy, bone marrow suppression makes infection a real danger, so protect neutropenic patients from germs.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).