Tumors are abnormal growths in the body. They develop when cells reproduce in an uncontrolled way. Usually, when old cells die, new ones may appear. In the case of tumors, the cells multiply too fast and do not die. This then gives rise to a mass. A benign tumor is one that is not cancerous.

Benign tumors do not spread and do not invade other parts of the body. They usually have defined borders, and most of the time, they will not recur if surgeons remove them.

A malignant tumor, however, is cancerous. This type of tumor may grow quickly and can spread to other parts of the body. Experts call the spread of cancer metastasis.

In this article, we explain whether benign tumors can become cancerous. We also list several types of tumor and discuss the characteristics of certain benign and cancerous tumors.

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Certain types of tumor, such as colon polyps, may become malignant. That is why doctors will recommend removing them.

It can be hard to predict how certain tumors will behave in the future, so doctors may keep monitoring them over time. These tumors are known as premalignant tumors.

Moreover, it is possible for a biopsy to miss an area where there are more cancer cells. Therefore, close monitoring of the tumor during follow-up appointments could reveal that it is cancerous.

Nevi is the medical term for common moles. These are small pink, tan, or brown growths on the skin. According to the National Cancer Institute, most adults will have 10–40 moles on their bodies.

Moles usually develop from late childhood through to around the age of 40. Older adults may notice that their moles fade over time.

A common mole will not usually turn into melanoma, which is a type of skin cancer. However, if a person has more than 50 moles, it is more likely that they will develop melanoma.

Is it cancerous?

A person should contact a doctor if they notice any of the following about their mole:

  • uneven changes in size
  • changes in color, shape, texture, or height
  • dry or scaly skin over the mole
  • the mole feeling hard or lumpy
  • itchiness
  • bleeding or oozing

See pictures of cancerous moles here.

Adenomas are tumors that develop in gland-like cells in the epithelial tissue. This is the tissue covering organs, glands, and other structures of the body.

Is it cancerous?

Adenomas are not cancerous, but some may turn into adenocarcinomas, which are a type of cancer.

Some forms of adenoma include:

  • Polyps in the colon: A person who has had a colonoscopy may learn they have polyps in the colon. A biopsy can determine whether the polyps are cancerous. If they are not, a person may need additional colonoscopies to ensure more polyps have not developed.
  • Hepatocellular adenomas: These rare benign tumors develop in the liver. In sporadic cases, they could become cancerous without treatment.
  • Fibroadenomas of the breast: These are the most common nonmalignant breast tumor. They do not become cancerous.

Fibromas are tumors that affect connective tissue within the body. There are many different types, including:

  • Dermatofibroma: This tumor usually develops on the lower legs.
  • Plantar fibroma: This type of tumor grows in the arch of the foot.
  • Ocular surface fibroma: This tumor develops in the eyes.

Is it cancerous?

Fibromas are not cancerous. They usually develop from tendons and fascia of the deep soft tissue.

In rare cases, fibromas may turn into fibrosarcomas, which are cancerous.

Fibrosarcoma may also affect the bone. Fibrosarcomas may be painless, but they may also cause:

Learn about possible causes of a hard bump under the skin here.

Desmoid tumors, which experts also refer to as desmoid-type fibromatosis or aggressive fibromatosis, grow from fibroblast cells, which form part of the connective tissue.

This type of tumor usually occurs in the arms, shoulders, legs, or abdomen.

Is it cancerous?

Desmoid tumors are benign but can also invade nearby tissue.

They can grow slowly or quickly, and they can be painful. Additionally, they can be difficult to remove through surgery and can recur after removal.

Hemangiomas, which people sometimes call strawberry marks, occur due to blood vessels growing at an abnormal rate. They are a common type of birthmark in children and can shrink over time.

Hemangiomas usually develop on the surface of the skin or just below, although some types can occur throughout the body. Treatment may not be necessary.

Learn about external hemangiomas here.

Is it cancerous?

Hemangiomas are very rarely cancerous. However, a person with hemangioma may wish to contact a doctor to remove it:

  • for cosmetic reasons
  • because some hemangiomas on the skin can cause difficulty breathing, seeing, or eating
  • as some hemangiomas develop in muscle or bone

Learn about internal hemangiomas here.

According to the American Academy of Orthopaedic Surgeons, lipomas are the most common soft tissue tumor in adults. They consist of fatty tissue and can develop in anyone, regardless of their body weight.

Lipomas most often affect people aged 40–60 years.

These soft tissue tumors commonly form on the arms, shoulders, upper back, buttocks, and upper thighs. They range in size, and lipomas that occur in deeper tissue tend to be larger when healthcare professionals discover them.

Is it cancerous?

Lipomas very rarely become cancerous or cause any other complications. However, people with a subtype called atypical lipoma may be more at risk of developing fatty cancer.

A person should monitor their lipoma over time with a doctor. Treatment for lipoma involves excision, or removal, of the fatty tissue. This may be necessary if the lipoma grows larger or if a person experiences pain or social discomfort as a result of the condition.

Fibroids, also known as leiomyomas, are the most common benign tumors that affect females of childbearing age. These masses consist of smooth muscle cells and other tissues that grow in the wall of the uterus.

Although benign, fibroids can cause pain and abnormal bleeding. They can also result in difficulty getting pregnant or maintaining pregnancy.

Currently, the only definitive cure is hysterectomy, which is the removal of a person’s uterus. Treatment for fibroids may involve medication, a short hospital stay, or various outpatient procedures.

Is it cancerous?

Fibroids are almost always noncancerous. However, fewer than 1 person in 1000 experiences a cancerous fibroid. Medical professionals do not believe that these cancerous fibroids start from preexisting fibroids.

Having fibroids does not increase a person’s risk of developing cancer of the uterus.

Learn about natural treatments for fibroids here.

If a person notices they have an unusual lump on their body, they should consult a doctor. A doctor may start by conducting a physical examination and, if possible, looking at the size and shape of the tumor.

In order to diagnose a benign tumor, the doctor may use imaging tests. Depending on the location of the lump or mass, the doctor can order:

Sometimes, a person will have one of these tests for an unrelated reason, and a doctor may notice a benign tumor.

Biopsies of the tumor may help doctors rule out cancer and, if necessary, determine the most appropriate course of treatment.

Benign tumors do not usually cause serious health complications. However, a person may wish to undergo a procedure to remove them, sometimes for cosmetic or practical reasons.

Some benign tumors have a small likelihood of becoming cancerous. If a person finds a lump or growth on or notices unusual changes to their body, they should contact a healthcare professional.