Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place.

When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed. These extra cells can divide without stopping and may form growths called tumors.

Many cancers form solid tumors, which are masses of tissue. Cancers of the blood, such as leukemias, generally do not form solid tumors.

Cancerous tumors are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor.

Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening.

In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing or that begin a process known as programmed cell death, or apoptosis, which the body uses to get rid of unneeded 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 instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumors with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumors.

Cancer cells are also often able to evade the immune system, a network of organs, tissues, and specialized cells that protects the body from infections and other conditions. Although the immune system normally 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 stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response, cancer cells can actually keep the immune system from killing cancer cells.

In metastasis, cancer cells break away from where they first formed (primary cancer), travel through the blood or lymph system, and form new tumors (metastatic tumors) in other parts of the body. The metastatic tumor is the same type of cancer as the primary tumor.

A cancer that has spread from the place where it first started to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis.

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

Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes.

Treatment may help prolong the lives of some people with metastatic cancer. In general, though, the primary goal of treatments for metastatic cancer is to control the growth of the cancer or to relieve symptoms caused by it. Metastatic tumors can cause severe damage to how the body functions, and most people who die of cancer die of metastatic disease.

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:

Hyperplasia occurs when cells within a tissue divide faster than normal and extra cells build up, or proliferate. However, the cells and the way the tissue is organized look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation.

Dysplasia is a more serious 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. 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.

An even more serious condition is carcinoma in situ. Although it is sometimes called cancer, carcinoma in situ is not cancer because the abnormal cells do not spread beyond the original tissue. That is, they 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.

Credit: Terese Winslow

Cancer Prevention is decreasing a person’s chance of having a cancer by taking certain actions. It aims to lower the number of people dying from cancer

Not all cancers can be prevented. There are risk factors that we cannot do something about like increasing age, genetic factors and family history. But there are also risk factors that can help avoid cancer by modifying the diet, lifestyle change and subjecting oneself to interventions such as cancer screening and vaccination.

Obesity is linked to several types of cancer and increasing physical activity lowers the risk of many types of cancer such as breast, endometrial, prostate, colorectal and lung cancers. Spending 3 hours of moderate exercise per week and getting up every hour from sitting will help mobilize the fats in the body.

Choosing the right food and eating the right amount can help in avoiding cancer. Good sources of vitamins, minerals and antioxidants are vegetables, legumes and whole grains. Protein is needed by our body and this can be found in meat and poultry products (beef, pork and chicken) but limiting it to 18 ounces of cooked meat per week is the key. Avoid preserved, salty and canned foods like hotdogs, bacon and sausages.

Smoking is a known risk factor for lung cancer, oropharyngeal and other types of cancer. Active smokers are at high risk and those who are exposed to secondhand smoke are still considered to be at risk. Smoking cessation is a global project as lung cancer is the top cancer causing death worldwide.

Exposure to ultraviolet rays is a risk factor for skin cancer. Avoiding the sun especially at noontime, wearing protective clothes and regular use of sunblock can prevent development of skin cancer.

Certain types of infection can lead to cancer. Human papillomavirus can cause genital warts and cancers such as cervical cancer, penile, anal and oropharyngeal cancer. Hepatitis B is linked to liver cancer. These can be prevented by having vaccination, so discuss with your doctor about having vaccination for you and your family at the earliest possible time.

There are certain cancers that can be prevented when discovered in early stages or in its precancerous stage by undergoing procedures. This is called Cancer Screening. Not all cancers can be screened. The individual who undergoes these procedures have no signs and symptoms. The screenable cancers are breast cancer, colorectal, lung, prostate and cervical cancers. Talk to your family doctor and medical oncologists about the specific procedures.

References:

National Cancer Institute
MD Anderson Cancer Center
NCCN