There are many conditions that can cause a lump under your skin. Since desmoid tumors (also known as aggressive fibromatosis or deep musculoaponeurotic fibromatosis) are rare, your health care provider may look for other causes if you notice any unusual growths. One potential cause of a lump is a dermoid cyst — a lump caused by a collection of tissue under the skin. This article will help you understand the similarities and differences between these two conditions.

6 Differences Between Desmoid Tumor and Dermoid Cyst

You may not be able to tell the difference between a desmoid tumor and a dermoid cyst just by looking. However, there are many differences between these two conditions.

1. Dermoid Cysts Contain Normal Tissues Found in an Abnormal Location

Dermoid cysts are made from normal tissues that are found in an abnormal location. Most dermoid cysts contain cells that look normal under a microscope but don’t belong in the area where they’re found. For example, a dermoid cyst may contain the following types of tissues:

• Skin cells
• Bone cells
• Hair
• Nerve cells
• Teeth
• Sweat glands

A dermoid cyst that contains sweat gland cells may make a greasy, yellow substance that makes the cyst grow larger.

Desmoid tumors are made up of a group of abnormal cells found in the connective tissue. Your connective tissue is the tissue that connects and gives structure to the organs in your body. Examples of connective tissue include tendons, ligaments, fat, and bone. Abnormal cells in a desmoid tumor are caused when a mutation (change) in the connective tissue cells causes them to grow and multiply abnormally.

2. Dermoid Cysts Can Be Present at Birth

Dermoid cysts can begin when a fetus is developing in the womb. If certain layers of skin grow in an atypical way, these cells may get trapped in a sac that can grow over time. When a dermoid cyst develops in the womb and is present at birth, it is called a congenital dermoid cyst.

People with desmoid tumors usually aren’t born with them. A desmoid tumor develops when something causes the cells in your connective tissue to grow rapidly. Certain risk factors are associated with an increased risk of developing a desmoid tumor, including:

• High estrogen levels
• Pregnancy
• Female sex
• Physical trauma or repeated injury
• Familial adenomatous polyposis (FAP, a genetic condition that increases your risk of certain cancers, particularly in the colon)

3. Most Dermoid Cysts Are Diagnosed in Children

Since dermoid cysts can be present at birth, it makes sense that most cases are diagnosed in children. About 40 percent of dermoid cysts are diagnosed in newborns. Of those not diagnosed at birth, most cases are diagnosed before age 5. Dermoid cysts are the most common cause of masses found on the scalp or skull of children.

Desmoid tumors can also be diagnosed in children, but most are diagnosed in people between the ages of 10 and 40.

4. Most Dermoid Cysts Occur on the Head and Neck

More than 80 percent of dermoid cysts are found on the head and neck. A periorbital dermoid cyst is the most common type of dermoid cyst. This type of dermoid cyst occurs near the eye.

Desmoid tumors commonly occur in the abdomen (stomach). Between 28 percent and 69 percent of desmoid tumors are abdominal or intra-abdominal. Abdominal wall desmoid tumors occur in the wall of your abdomen, in the fat or muscles. Intra-abdominal desmoid tumors grow inside your abdomen in the tissues that surround your intestines, called the mesentery.

5. Dermoid Cysts Can Rarely Become Cancerous

In rare cases, ovarian dermoid cysts can become cancerous. It’s estimated that less than 2 percent of ovarian dermoid cysts eventually become cancerous. The risk of an ovarian dermoid cyst becoming cancerous may be higher in people older than 45 years with a large, fast-growing cyst.

Desmoid tumors, on the other hand, are considered aggressive, but they are slow-growing and only locally invasive.

6. Desmoid Tumors May Require Cancer Treatments

Some types of desmoid tumors may require treatments similar to those for various types of cancer, such as soft tissue sarcomas. Cancer treatments may help shrink some types of desmoid tumors by killing the abnormal cells found in the tumor.

Cancer treatments that may be used to treat desmoid tumors include:

• Targeted therapy
• Chemotherapy
• Radiation therapy
• Cryoablation

Dermoid cysts are not treated with the above cancer therapies because they don’t contain abnormal cells, but if necessary, they can be removed with surgery.

4 Similarities Between Desmoid Tumor and Dermoid Cyst

Although there are many differences between desmoid tumors and dermoid cysts, there are also some similarities.

1. Desmoid Tumors and Dermoid Cysts Do Not Spread

A desmoid tumor is considered an aggressive tumor, but this type of tumor doesn’t spread to other parts of the body like a cancerous tumor can.

Dermoid cysts are slow-growing masses filled with old skin, fluid, or other substances. Dermoid cysts are not considered to be cancerous and do not spread to other parts of the body.

2. Both Types Can Occur Anywhere on the Body

Dermoid cysts commonly occur on the head or neck, but they may appear anywhere on the body. Other possible locations of dermoid cysts include:

• Ovaries
• The spine
• Eyes
• The brain
• The nose

Desmoid tumors can affect any part of the body, but often affect the abdomen. Desmoid tumors that occur outside of the abdomen are called extra-abdominal desmoid tumors. This type can occur on various parts of the body, including these:

• Arms
• Legs
• Shoulders
• Head and neck

3. Desmoid Tumors and Dermoid Cysts Can Begin To Cause Symptoms as They Grow Bigger

People with a dermoid cyst or desmoid tumor may not have any symptoms, especially if the tumor or cyst is small. However, as the lump gets larger, it can affect surrounding organs and cause symptoms.

For example, an ovarian dermoid cyst or abdominal desmoid tumor can cause symptoms such as:

• Abdominal pain
• Constipation or bowel obstruction
• Nausea and vomiting
• Abdominal enlargement
• Bloatedness

People with a desmoid tumor on their leg or a dermoid cyst on their spinal cord may have difficulty walking or moving their legs.

4. Diagnosis of Desmoid Tumors and Dermoid Cysts Involves Imaging

Imaging tests can help health care providers tell the difference between a desmoid tumor, a dermoid cyst, or other causes of lumps, like more serious cancers.

Imaging tests help you get a better picture of the inside of the body. A few kinds of imaging tests may help diagnose these conditions, including computed tomography (CT) scans and magnetic resonance imaging (MRI) scans. An ultrasound scan can help health care providers diagnose ovarian dermoid cysts.

If your provider suspects your lump is a desmoid tumor, they will also order a biopsy — a procedure in which a sample of affected tissue is removed and examined under a microscope.

Talk With Others Who Understand

MyDesmoidTumorTeam is the social network for people with desmoid tumors and their loved ones. On MyDesmoidTumorTeam, members come together to ask questions, give advice, and share their stories with others who understand life with desmoid tumors.

Do you have questions about the similarities and differences between desmoid tumors and dermoid cysts? Have you experienced either of these conditions? Share your experience in the comments below, or start a conversation by posting on your Activities page.