Cancer

03Oct 2021 by Hala Ahmad 1 Comment

The Definition of Cancer

Cancer is a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body.

Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and multiply (through a process called cell division) to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.

Sometimes this orderly process breaks down, and abnormal or damaged cells grow and multiply when they shouldn’t. These cells may form tumors, which are lumps of tissue. Tumors can be cancerous or not cancerous (benign).

Cancerous tumors spread into, or invade, nearby tissues and can travel to distant places in the body to form new tumors (a process called metastasis). Cancerous tumors may also be called malignant tumors. Many cancers form solid tumors, but cancers of the blood, such as leukemias, generally do not.

Benign tumors

Are not cancer
Can usually be removed
Don’t come back in most cases
Don’t spread to other parts of the body, and the cells don’t invade other tissues
Are rarely a threat to life

Malignant tumors

Are cancer and may be a threat to life
Can invade and damage nearby tissues and organs
Can spread or metastasize. Cancer cells break away from a malignant tumor and move through the bloodstream or lymphatic system to form tumors in other parts of the body.

Tissue Changes that Are Not Cancer

Not every change in the body’s tissues is cancer. Some tissue changes may develop into cancer if they are not treated, however. Here are some examples of tissue changes that are not cancer but, in some cases, are monitored because they could become cancer:

Hyperplasia occurs when cells within a tissue multiply faster than normal and extra cells build up. However, the cells and the way the tissue is organized still look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation.
Dysplasia is a more advanced condition than hyperplasia. In dysplasia, there is also a buildup of extra cells. But the cells look abnormal and there are changes in how the tissue is organized. In general, the more abnormal the cells and tissue look, the greater the chance that cancer will form. Some types of dysplasia may need to be monitored or treated, but others do not. An example of dysplasia is an abnormal mole (called a dysplastic nevus) that forms on the skin. A dysplastic nevus can turn into melanoma, although most do not.
Carcinoma in situ is an even more advanced condition. Although it is sometimes called stage 0 cancer, it is not cancer because the abnormal cells do not invade nearby tissue the way that cancer cells do. But because some carcinomas in situ may become cancer, they are usually treated.

Normal cells may become cancer cells. Before cancer cells form in tissues of the body, the cells go through abnormal changes called hyperplasia and dysplasia. In hyperplasia, there is an increase in the number of cells in an organ or tissue that appear normal under a microscope. In dysplasia, the cells look abnormal under a microscope but are not cancer. Hyperplasia and dysplasia may or may not become cancer.

What are the general categories of cancers?

There are general categories of cancer based on the type of cell the cancer starts in. Carcinomas and, more specifically, adenocarcinomas are the most common type:

Carcinomas. Cancers that start in epithelial surfaces. These surfaces are the cells that form the outer surface in the body to line or cover the body’s organs, cavities, tubes, and passageways. These cancers form solid tumors.

Adenocarcinomas. Cancers that start in glandular tissues that make mucus or fluid, such as the lung, breast, prostate, or colon. Adenocarcinomas are considered a specific type (subtype) of carcinomas

Sarcomas. Cancers that start in cells that make up supporting structures, such as bone, muscle, cartilage, fat, or fibrous tissue. These cancers form solid tumors

Leukemias. Cancers that start in blood cell, most often white blood cells. Because these cancers are in the blood cells, they don’t cause tumors.

Lymphomas. Cancers that start in cells of the lymph nodes and lymphatic system. They may cause tumors in lymph tissue.

Multiple Myeloma Multiple myeloma is cancer that begins in plasma cells, another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumors in bones all through the body. Multiple myeloma is also called plasma cell myeloma and Kahler disease.
Melanoma Melanoma is cancer that begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color). Most melanomas form on the skin, but melanomas can also form in other pigmented tissues, such as the eye.

Brain and Spinal Cord Tumors There are different types of brain and spinal cord tumors. These tumors are named based on the type of cell in which they formed and where the tumor first formed in the central nervous system. For example, an astrocytic tumor begins in star-shaped brain cells called astrocytes, which help keep nerve cells healthy. Brain tumors can be benign (not cancer) or malignant (cancer)

What are primary cancers?

Cancers start in a single cell that has been damaged (mutated). That cell is the source of the primary cancer. The cancer is always named for the primary site where the original or first tumor started, such as skin, colon, or breast.

What are metastatic cancers?

Cancer can spread from where it started (the primary site) to other parts of the body.

The cancer may spread by directly entering nearby tissues.
The cancer may spread throughout the body. This is called systemic spread. The cancer cell may get into and travel through the:
- Blood system. Arteries and veins take blood to and from all areas of the body.
- Lymphatic system. A network of lymphatic vessels in all areas of the body that drain and filter infectious agents.

A cancer cell can travel through these systems. With time, the cancer cell can grow and form a new tumor that may not be near the primary site. When cancer spreads to another part of the body, it is called metastatic cancer.

Metastatic cancer is still named for the primary site. For example:

When cancer that started in the colon is found in the liver, it’s called colon cancer that has metastasized to the liver. It is not called liver cancer.
Lung cancers are those that started from a lung cell. If the cancer spreads to the brain, it’s called metastatic lung cancer, not brain cancer.
When cancer spreads to the nearby lymph nodes, those nodes are said to contain metastatic cancer. (Cancers that start in the lymph cells of a node are called lymphomas.)

If cancer cells are taken out from the metastatic tumor, they will look like the primary cancer cells. These metastatic tumors are also treated like the primary tumors. So colon cancer that has spread or metastasized to the liver is still treated like colon cancer is treated. The cells in the metastatic liver tumor look like the primary cancer cells in the colon. It’s not liver cancer, it didn’t start in liver cells. It’s metastatic colon cancer.

Cancer can metastasize to any part of the body, but the most common sites are: