Cancer causes and types

Cancer is the name given to a group of related diseases. In all types of cancer, some cells of the body begin to divide non-stop and spread in surrounding tissues. Cancer can start almost anywhere in the human body, which consists of trillions of cells. Normally, human cells grow and divide to form new cells as needed by the body. When cells grow or are damaged and new cells take their place.

When cancer develops, this structured process breaks down. When cells become increasingly abnormal, old or damaged cells live when they must die, and new cells form when they are not needed. These excess cells can divide non-stop and may form a growth called tumors.

Cancers are generally divided into two types of malignant cancers and metastasis cancers.

Cancerous tumors are malignant cancers, which means they can spread to nearby tissues or invade them. In addition, as these tumors develop, some cancer cells can separate and move to distant places in the body through the blood or lymphatic system and form new tumors far from the original tumor.

Unlike malignant tumors, benign tumors do not spread or invade nearby tissues. Benign tumors can sometimes be very large. When removed, they usually do not grow back, while malignant tumors sometimes grow. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life-threatening.

Differences between cancer cells and normal cells

Cancer cells differ from normal cells in many ways that allow them to grow out of control and become invasive. One important difference is that cancer cells are less specialized than normal cells. That is, while normal cells mature into very characteristic cell types with specific functions, cancer cells do not mature. This is one of the reasons why cancer cells, unlike normal cells, continue to divide non-stop.

In addition, cancer cells are able to ignore signals that usually require cells to stop splitting or begin a process known as apoptosis that the body uses to get rid of unnecessary cells.

Cancer cells may be able to influence the normal cells, molecules and blood vessels that surround and feed a tumor – an area known as the microenvironment. For example, cancer cells can stimulate nearby normal cells to form blood vessels that provide tumors with the oxygen and nutrients they need to grow. These blood vessels also remove waste from tumors.

Cancer cells are also often able to evade the immune system, a network of organs, tissues and specialized cells that protect the body from infection and other conditions. Although the immune system usually removes damaged or abnormal cells from the body, some cancer cells are able to “hide”, from the immune system.

Tumors can also use the immune system to survive and grow. For example, with the help of some immune system cells that usually block a runaway immune response, cancer cells can actually prevent the immune system from attacking them.

How cancers form

Cancer is a genetic disease – that is, it is caused by changes in genes that control the way our cells work, especially how they grow and divide.

Genetic changes that cause cancer can be inherited from our parents. It can also arise during a person’s life as a result of errors that occur when cells are divided or because of DNA damage due to environmental exposure. Carcinogenic environmental exposures include substances, such as chemicals found in tobacco smoke, and radiation, such as ultraviolet radiation from the sun.

Each person’s cancer contains a unique set of genetic changes. As cancer continues to grow, additional changes will occur. Even within the tumor itself, different cells may have different genetic changes.

In general, cancer cells contain more genetic changes, such as mutations in DNA, than normal cells. Some of these changes may not have to do with cancer.

“Engines” Cancer

Genetic changes that contribute to cancer tend to affect three main types of genes – primary genes of tumor genes, tumor suppression genes, and DNA repair genes. These changes are sometimes called “engines” cancer.

Primitive genes are involved in the growth and division of cells naturally. However, when these genes are altered in certain ways or are more active than usual, they may become carcinogenic (or cancer genes), allowing cells to grow and survive when they should not.

Tumor inhibitor genes are also involved in controlling cell growth and division. Cells containing certain modifications in tumor suppressor genes may be divided in an uncontrolled way.

DNA repair genes are involved in the repair of damaged DNA. Cells with mutations in these genes tend to develop additional mutations in other genes. Together, these mutations can cause cells to become cancerous.

As scientists have learned more about the molecular changes that lead to cancer, they have found that some mutations occur commonly in many cancers. For this reason, cancers are sometimes characterized by the types of genetic changes that are thought to lead them, not only in terms of where they develop in the body and how cancer cells look under a microscope.

What happens when the cancer spreads?

Cancer, which has spread from where it first began to another place in the body, is called metastasis and the process by which tumor cells spread to other parts of the body called metastases.

Metastatic cancer has the same name and type of tumor cells as the original or primary cancer. For example, breast cancer that turns into a malignant tumor that spreads in the lung is metastatic breast cancer, not lung cancer.

Under the microscope, metastatic cancer cells generally look like the original tumor cells. Furthermore, mutated cancer cells and original cancer cells usually have some common molecular features, such as specific chromosomal changes.

Treatment may help prolong the lives of some people with metastatic cancer. In general, however, the primary goal of metastatic tumor treatments is to control the growth of a tumor or relieve the resulting symptoms. Metastases can cause serious damage to how the body works.

Non-cancerous tissue changes

Not every change in body tissues is cancer. Some tissue changes may develop into cancer if not treated. Here are some examples of non-cancerous tissue changes, but in some cases, they are monitored:

  • Hyperplasia occurs when cells within the tissue divide faster than normal cells and additional cells accumulate or multiply. However, cells and the way tissue is regulated appear normal under a microscope. Hyperplasia can occur due to several factors or conditions, including chronic irritability.
  • Dysplasia is a more serious condition of inflation. In dysplasia, there is also an accumulation of additional cells. But cells look abnormal and there are changes in how tissues are regulated. In general, the more cells and tissues appear abnormal, the greater the chance that cancer will form. Some types of dysplasia may need to be monitored or treated. An example of dysplasia is an abnormal mole (called dysplasia) formed on the skin. Dysplasia can turn into skin cancer, although most of them do not.
  • A more serious condition is on-site cancer. Although it is sometimes called tumor , on-site tumor is not cancer because abnormal cells do not spread outside the original tissues. That is, they do not invade nearby tissues in the way cancer cells do. However, since some on-site cancerous tumors may become cancer, they are usually treated.


There are more than 100 types of cancer. Cancers are usually named for organs or tissues where tumors are formed. For example, lung cancer begins in lung cells, and brain tumor begins in brain cells. Cancer can also be described as the type of cell it formed, such as epithelial cells or squamous cells.

Here are some categories of cancers that begin in certain types of cells:

Cancerous tumor

Cancerous tumors are the most common cancers. It consists of epithelial cells, cells that cover the inner and outer surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when displayed under a microscope.

Cancerous tumors that begin in different types of epithelial cells have specific names:

  1. Glandular tumor is a cancer formed in epithelial cells that produce fluid or mucus. The tissues that contain this type of epithelial cell are sometimes called glandular tissue. Most breast, colon and prostate cancers are Adenoma tumors.
  1. Basal cell carcinoma is a tumor that begins in the lower or basal layer of the skin, which is the outer layer of the skin.
  2. Squamous cell carcinoma is a tumor formed in squamous cells, which are epithelial cells located beneath the outer surface of the skin. Squamous cells also line many other organs, including the stomach, intestines, lungs, bladder and kidneys. Squamous cells look flat, like fish shells, when displayed under a microscope. Squamous cell carcinoma is sometimes called skin cancer.
  3. Transitional cell carcinoma is a tumor formed in a type of epithelial tissue called transitional epithelium, or urinary epithelium. This tissue, which consists of many layers of epithelial cells that can become larger and smaller, is found in the linings of the bladder, ureter, part of the kidneys (renal pelvis), and a few other organs. Some bladder, ureter and kidney cancers are transitional cell carcinoma.


Sarcomas are cancers formed in bones and soft tissues, including muscles, fat, blood vessels, lymphatic vessels and fibrous tissues (such as tendons and ligaments).


Cancers that begin in bone marrow are called leukemia. These cancers do not form solid tumors. Instead, large numbers of abnormal white blood cells accumulate in the blood and bone marrow, leading to the congestion of normal blood cells. A low level of normal blood cells can make it difficult for the body to access oxygen to its tissues, control bleeding, or fight infection.

There are four common types of leukemia, which are collected based on how quickly the disease (acute or chronic) worsens and on the type of blood cell in which cancer begins (lymphoma or myeloma).


Lymphoma is a cancer that begins in lymphocytes (T cells or B cells). They are white blood cells that fight diseases and form part of the immune system. In lymphoma, abnormal lymphocytes accumulate in lymph nodes and lymph vessels, as well as in other organs of the body.

There are two main types of lymphoma:

Hodgkin’s lymphoma: People with this disease have abnormal lymphocytic cells called Red Sternberg cells. These cells are usually made up of B cells.

Non-Hodgkin’s lymphoma: It is a large group of cancers that begin in lymphocytes. Cancers can grow rapidly or slowly and can consist of B cells or T cells.

Multiple myeloma

Multiple myeloma is a cancer that begins in plasma cells, another type of immune cell. Abnormal plasma cells, called myeloma cells, accumulate in the bone marrow and form tumors in the bones throughout the body. Multiple myeloma is also called plasma cell myeloma and Kahler’s disease.

Skin cancer

Melanoma is a cancer that begins in cells that become pigment cells, which are specialized cells that make melanin (the dye that gives the 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 were formed and where the tumor first formed in the central nervous system. For example, astral tumor begins in star-shaped brain cells called astral cells, which help maintain the health of neurons. Brain tumors can be benign or malignant.

Other types of tumors

Germ cell tumors

Germ cell tumors are a type of tumor that begins in cells that lead to the appearance of sperm or eggs. These tumors can occur almost anywhere in the body and can be benign or malignant.

Neuroendocrine tumors

Neuroendocrine tumors are made up of cells that release hormones into the blood in response to a signal from the nervous system. These tumors, which may produce larger than usual amounts of hormones, can cause many different symptoms. Neuroendocrine tumors may be benign or malignant.

Carcinoid tumors

Carcinoid tumors are a type of neuroendocrine tumor. Slow-growing tumors are commonly found in the digestive tract (mostly in the rectum and small intestine). Carcinoid tumors may spread to the liver or other sites in the body, and substances such as serotonin or prostaglandin may be secreted, causing