discovery

What is a tumor?

Key points:

  • A tumor is an abnormal collection of cells in the body. Tumors can be benign, pre-cancerous or cancer.
  • A benign tumor is not cancer, it does not spread to other organs, it tends to be small, and it doesn’t grown aggressively. If removed, it’s less likely to come back. Some types of benign tumors can eventually become cancerous tumors.
  • Precancerous tumors contain cells that are already beginning to change their behavior to become distinctly abnormal. They have some abnormalities (mutations) in the DNA, but they are fewer than the changes to the DNA in established cancer. They look different to [normal cells].
  • Precancerous tumors may lead to a cancerous tumor but they may disappear or remain pre-cancerous.
  • If the conditions that led to the development of a pre-cancerous condition are changed, it can help to prevent the pre-cancerous condition becoming a cancer.
  • A cancerous tumor is a collection of malignant cells that has managed to avoid destruction by the immune system. Compared with benign tumors, malignant tumors are generally faster growing, and they behave differently to benign tumors. They can invade surrounding tissue and may spread to other organs.
  • Tumors can be classified according to their location within the body, and also classified by the type of tissue that they have developed in.
  • The risk of developing some cancers are not thought to be modifiable by behavioral choices. On the other hand, some lifestyle factors such as smoking, alcohol and diet can influence the risk of developing some types of cancer.

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Cancers are becoming more common1, for many reasons. Cancer is not one single disease, but a collection of conditions where cell behavior has become deranged. In this article, we’ll look at what a tumor is, and some common tumor types.

Types of tumor

A tumor is an abnormal collection of cells in the body2. Tumors can be benign, pre-cancerous or cancer. We’ll look at the differences between these and the effects they may have in the body. We’ll also look briefly at some types of tumors that are open to influence by diet, exercise and other lifestyle choice.

What is a benign tumor?

A benign tumor is not cancer, it does not spread to other organs, it tends to be small, and it generally doesn’t grow aggressively. If removed, it’s less likely to come back. Common benign tumors include bowel polyps, breast fibroadenoma and fibromas (fibroids) in the uterus. Very common benign tumors are lipomas, which are fatty tumors that may develop under the skin. There are also several types of benign skin tumors, and benign brain tumors such as acoustic neuromas. Some of these benign tumors cause few symptoms, but others can cause problems because they block a blood vessel or take up space within an organ. Fibromas in the uterus can cause heavy bleeding and pain. Benign brain tumors can cause significant harm, and even be fatal if not treated, as they expand within the skull and create pressure in the brain.

Benign tumors may develop due to injury or inflammation, for example polyps on the tongue may develop due to abrasion against damaged or misaligned teeth.

Some types of benign tumors can eventually become cancerous tumors. For example, bowel polyps, particularly some types of bowel polyps, may become pre-cancerous and eventually lead to bowel cancer.

Cigarette smoke

What does precancerous mean?

Cells within tumors that are pre-cancerous are already beginning to change their behavior. Examples are pre-cancerous tumors on the uterine cervix4, which can be detected by a cervical Pap test. Cells in these pre-cancerous tumors have begun to be abnormal; they start to look different to [normal cells] (dysplasia). Depending on the degree of abnormality they may lead to a cancerous tumor but they may disappear or remain pre-cancerous.

What influences a precancerous condition becoming a cancerous tumor?

Pre-cancerous cells have some abnormalities (mutations) in the DNA.  They happen because the cell has been exposed to [carcinogens] such as UV light, tobacco smoke, alcohol, some dietary factors and environmental contaminants. Abnormalities in the DNA within cells are also more common with age, due to accumulation of mistakes in the [division of cells]. In precancerous tumors there are fewer DNA abnormalities than the changes to the DNA in established cancers3. Abnormalities in the DNA affect the behavior of the cell. If the conditions that led to the development of a pre-cancerous condition are changed, it may help to prevent the pre-cancerous condition becoming a cancer. For example, leukoplakia is a pre-cancerous tumor in the mouth that is linked to smoking5. If a person with leukoplakia quits smoking that may reduce their risk of leukoplakia progressing to mouth cancer. A healthy immune system is primed to detect and attack pre-cancerous tumours, but in some cases this isn’t sufficient to keep control of a precancerous tumor.

After a cell has begun to be transformed to a cancer cell, there are many steps along the way that influence the development of cancer as a disease6-8. Some pre-cancerous conditions and early cancers may never become a problem, they may never even be detected as the immune system may find them and destroy them before they become established.

What is the difference between a malignant tumor and a benign tumor3?

A cancerous (malignant) tumor is a collection of malignant cells that has managed to avoid destruction by the immune system. Malignant tumors are generally faster growing, and they behave differently to benign and precancerous tumors. The cell and tissue structure is also different to benign tumors and normal tissue. They key distinguishing feature of malignant tumors is that they can invade surrounding tissue and may spread to other organs. As they grow larger, malignant tumors induce new blood vessels (angiogenesis) to sustain the supply of oxygen and nutrients (we discuss this in our [Video Series]). They may secrete factors to disarm the immune system. Malignant tumors may release cells that spread to other parts of the body to produce secondary tumors [(metastases)]. Many new cancer treatments target these behaviors of tumors to control the disease, by re-enabling the body’s defenses to attack cancer cells, or blocking the development of new blood vessels within a tumor.

Three parts of a cell - nucleus, cytoplasm and membrane

What are the main types of cancerous tumor2?

Tumors can be classified according to their location within the body, for example breast, liver or brain. Tumors are also classified by the type of tissue that they have developed in.  Most solid tumors are carcinomas, which develop in the layers of tissue that cover the surfaces inside and outside organs, the epithelial tissue. Breast carcinomas may develop in the lining of the milk ducts in the breast, for example.

Sarcomas are tumors that develop within the bones and soft tissues of the body such as muscles and tendons. Germ cell tumors develop in the tissue that leads to the production of sperm or eggs, for example some types of testicular tumors. There are several types of cancerous brain tumor, developing in the different tissues in the brain.

What may be done to help prevent a precancerous condition becoming a cancerous tumor9-12?

Let’s look at a common location of tumors and some factors that can affect the chances of a benign or pre-cancerous tumor becoming a cancer. For some cancers, risk factors have not been clearly identified, or they are not modifiable by behavioral choices. On the other hand, some lifestyle factors such as smoking, alcohol, lack of exercise, being overweight and diet can influence the risk of developing many types of cancer.  Research is ongoing to understand better just how important modifiable lifestyle factors are.

Many types of cancers affecting the digestive system are influenced by diet. Polyps are common benign tumors that occur in the bowel13. They may be detected by a colonoscopy, when they may be removed and examined by a pathologist. Polyps are sometimes hereditary, in this case frequent medical examination can help detect them and remove them before a cancerous tumor has developed.

What are the dietary factors that may affect the risk of benign or precancerous polyps leading to a colon tumor?

Dietary factors that influence the risk of developing benign polyps, precancerous conditions and bowel cancer have been studied. A high intake of red meat and a low intake of fiber are each linked to greater cancer risk, though it should be noted that most studies don’t distinguish higher quality meat from highly processed and lower quality meat. Low levels of physical activity and higher body fat also increase risks of developing a cancerous tumor in the bowel. Changes in the population of microbes (the microbiome) in the intestine are also implicated. Studies of the microbiome in people who have developed colon cancer suggest they have less diverse microbiomes and may be missing some very beneficial species of bacteria. One of the benefits of eating a lot of different vegetables is this may give a more balanced population of microbes.

See our article on [cancer fighting foods] for more information.

What other factors may influence why some precancerous conditions become cancer?

Viruses can cause cancer

In some precancerous conditions, having type 2 diabetes or persistently elevated blood sugar may increase the chances of a precancerous condition becoming cancerous. Leukoplakia in the mouth is more likely to lead to mouth cancer in people with high blood sugar levels5. Inflammation in the area around a precancerous tumor may increase the risk of progression, for example inflammation linked to the presence of some strains of human papillomavirus (HPV) may increase the risk of developing cervical cancer from a precancerous cervical lesion.

Summary

In this article we have identified that tumors can be benign, which are generally slow growing, not invasive and may cause no health problems. Some benign tumors especially those in the brain can be very serious. Precancerous tumors have some abnormalities but are not yet an invasive cancer. Cancerous tumors can emerge from precancerous conditions, and some lifestyle factors can influence the risk of progression from precancerous to cancerous. There are several different types of cancerous tumors, which can be classified according to their location in the body and the type of tissue where they have developed.

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