Cancer & Stem Cells

Many different diseases are called cancer. They involve cells multiplying beyond the body's normal controls.

A cell usually follows the cell cycle, with checkpoints that test whether it is ready to divide. Two groups of genes help control this process.

Proto-oncogenes encourage division when it is needed. Think of them as an accelerator. Certain mutations turn them into oncogenes, which can keep sending growth signals when division should stop.

Tumor suppressor genes help restrain division and support checks and repairs to DNA. They act like brakes. Mutations that disable these controls can let cells divide despite DNA damage.

Cancer usually develops after several changes accumulate, often affecting both gene groups. These changes have longer to collect as people age. This helps explain why cancer occurs more often in older adults.

Uncontrolled division can produce a tumor, although some cancers do not form lumps. Cells from some tumors can leave their original site and spread elsewhere. Learning how these control genes work helps researchers develop treatments aimed at cancer cells.

Most body cells with nuclei carry essentially the same DNA. Yet skin and muscle cells use different genes, giving them different features. Controlling which genes are active is called gene regulation. Disrupted regulation can contribute to cancer.

Although cancers differ, they share a loss of normal growth controls. Changes in gene activity can allow cells to continue growing and dividing when they should stop.

Problems can affect a gene's DNA, the copying of DNA into RNA or the making of a protein from RNA. Altered DNA packaging can also change which genes are available for use and contribute to cancer.

Researchers can identify some faulty gene controls in a patient's cancer. This can guide drugs toward particular proteins driving that cancer, rather than broadly targeting rapidly dividing cells. Such treatments can still affect healthy cells. Better knowledge of gene regulation helps scientists develop more specific treatments.

Most cells in your body have one fixed job. A red blood cell carries oxygen, a nerve cell sends signals, and that is all it will ever do. These are specialised cells.

Stem cells are different. A stem cell is unspecialised: it has not picked a job yet. It can do two special things. First, it can copy itself over and over, making more stem cells. Second, it can differentiate, which means it can turn into a specialised cell, like a blood cell, a skin cell, or a muscle cell.

This makes stem cells incredibly useful to your body. When you cut your skin, stem cells help build new skin. Your bone marrow holds stem cells that make fresh blood cells every day of your life.

Doctors hope to use stem cells in regenerative medicine, which means repairing or replacing damaged body parts. Imagine growing new heart cells for someone whose heart was damaged, or new nerve cells for someone with Parkinson's disease. Scientists are also testing whether stem cells can deliver gene therapy, carrying corrected DNA into the body.

There are different types of stem cells. Embryonic stem cells can become almost any cell type, while adult stem cells usually make only a few types. That difference is at the heart of both the science and the ethics debates around stem cell research.

Does it really matter how carefully a cell controls its division? Ask a cancer doctor, and the answer is a very clear yes.

Cancer is basically a disease of uncontrolled cell division. It usually develops through a series of changes in the molecules that regulate the cell cycle. Your cells have built-in regulators that work like traffic lights. Some are inhibitors, the red lights that stop a cell from dividing when conditions are wrong, for example when its DNA is damaged. Others are activators, the green lights that let division go ahead when everything is in order.

Trouble starts when mutations change these regulators. If a red light gene stops working, a damaged cell divides when it should have paused for repairs. If a green light gene gets stuck on, the cell divides again and again without waiting for a proper signal.

One famous red light is a protein called p53, sometimes nicknamed the guardian of the genome. When p53 finds serious DNA damage, it can stop the cell cycle or even instruct the cell to destroy itself. Mutations that disable p53 are found in a huge number of human cancers.

Knowing which traffic light has failed in a tumor helps doctors choose treatments that fit that exact cancer.

When a cell moves through the cell cycle, does it just rush from one stage to the next? If it is a cancer cell, sometimes the answer is yes. Healthy cells, though, move through the cycle in a careful, regulated way.

A cell uses information about itself and its surroundings to decide whether to divide. It asks questions like: Is my DNA copied correctly? Is there enough room and food? Are neighboring cells telling me to divide? If the answers are no, the cell waits.

These decision points are called checkpoints. At a checkpoint, the cell cycle pauses while the cell checks that everything from the last stage finished properly. If the cell finds damaged DNA, it can stop and repair it before dividing. If the damage cannot be fixed, the cell can trigger its own death, a process called apoptosis, so the mistakes are never passed on.

Checkpoints protect you every single day. They make sure cells do not divide under bad conditions, which keeps small copying errors from piling up.

Cancer cells are cells whose checkpoints have failed. Mutations have broken the inspection system, so the cells divide even when they are damaged. That is why studying checkpoints matters: it shows scientists exactly which safety systems cancer has switched off, and how they might be switched back on.