What is Cancer?
Cancer is not a single disease; it is actually a large group of diseases in which cells divide without stopping. These rapidly growing cells can spread into or attack surrounding tissues.
The human body is made of trillions of cells. As cells age, get damaged, or die, the body makes new ones. With cancer cells, this process stops working. Instead of dying off as they get old, cancer cells survive; new cells form when the body does not need them. Extra cells accumulate without stopping and come together to form growths called tumors.
Types of tumors
Some cancers grow into solid tumors but others, like leukemia, form in the bloodstream. Not all tumors are cancerous. Some tumors are called benign. This is because they are made of cells that do not break off and invade surrounding tissues or organs. Benign tumors are not made of cancerous cells. Cancerous tumors are called malignant because their cells can break off and invade other cells, tissues, and organs. Malignant cells can spread from the original site and start new tumors. Metastasis is the name for this process of malignant cells traveling to and attacking new areas of the body.
Malignant tumors can grow back if they are removed through surgery. Benign tumors can be very large but they do not grow back if surgically removed. Benign tumors also do not spread to other parts of the body. Except in rare cases like in the brain, benign tumors are not dangerous.
Cancer cell survival strategies
When it is time for normal cells to die, it happens in a systematic way. This process of programmed cell death is called apoptosis. It’s designed to get rid of old, damaged, or unnecessary cells. Cancer cells are able to ignore or block signals that tell normal cells to stop growing and start apoptosis.
To survive and grow, cancer cells influence normal cells and molecules to create new networks of blood vessels. These blood vessels bring oxygen and nutrients to the tumor and remove waste products.
Another way cancer cells live and grow is by hiding from the immune system, which normally removes damaged or abnormal cells from the body. Cancer cells can also use some of the immune system’s control mechanisms to avoid being killed by immune cells.
A disease of mutation
Cancer is denetic. It develops from changes (mutations and other abnormalities) in the genes, which govern the function of cells, especially how they grow and divide. These genetic changes can be inherited from our parents or come from environmental factors like tobacco smoke or UV rays from the sun.
In each person with cancer, the disease has a unique set of genetic changes. These changes often evolve as the cancer grows. Different cells within a single tumor can have a variety of genetic changes. DNA mutations happen more often in cancer cells than in normal cells.
Precursors of cancer
Cellular changes in various tissues do now always develop into cancer, but these 3 precursors may require monitoring:
- Hyperplasia. Rapid cell division is the primary characteristic of hyperplasia, but the shape, structure, and arrangement of these cells look normal under a microscope. Several conditions, such as chronic irritation, can lead to hyperplasia
- Dysplasia is more serious than hyperplasia. It also involves the accelerated buildup of extra cells, but with dysplasia the cells look abnormal under the microscope. The chance of dysplasia forming into cancer increases as the cells appear more and more abnormal. Some dysplasias may require monitoring or treatment
- Carcinoma in situ is an even more serious precursor. Though it is sometimes referred to as cancer, carcinoma in situ is not cancer. The reason is that the abnormal cells do not metastasize or invade other tissues. However, some carcinomas in situ require treatment to prevent them from becoming cancerous
There are over 100 types of cancer. Most often, they are named for the original location, such as lung cancer or brain cancer. Others are named for the type of cells involved, like squamous cell cancer or epithelial cell cancer.