Biology Within

Fibrosis is a slow buildup of tough, fiber-rich tissue inside an organ. It happens when the body keeps trying to repair damage that does not stop. Over time, this extra tissue crowds out working cells and leaves organs such as the liver, lungs, kidneys and heart stiff and less able to do their jobs.

The body heals a wound in a set order of steps. First it stops the bleeding, then it cleans the area, then it builds new tissue and new skin, and finally it makes the repair stronger. Most small wounds close within a few weeks, but the strengthening goes on quietly for a year or more.

A tumor is not just a lump of cancer cells. Cancer cells live among normal cells, blood vessels, protein fibers and chemical signals, and these surroundings are called the tumor microenvironment. Cancer cells change their surroundings so that they feed the tumor, shield it from the immune system, help it spread and protect it from treatment.

Cancer can return years after treatment because a small number of cancer cells can survive treatment without being found. Some of these cells stop dividing and rest quietly in the body, sometimes for years. If something later wakes them up, or the immune system stops holding them back, they can grow into a new tumor.

Cancer treatment can stop working when some cancer cells survive it and keep growing. This is called drug resistance. It can be present from the start or develop during treatment, as cancer cells change the drug's target, push drugs out, repair damage or switch to a new growth signal. This guide explains how each of these happens and what doctors do about it, in plain language.

A tumor is not a mass of identical cells. As a cancer grows, its cells pick up new changes and are shaped by the conditions around them, which are not the same in every part of the tumor. The result is a mix of cell groups that can grow at different speeds, spread differently and respond differently to treatment.