What is a Desmoid Tumor?
Desmoid tumors (also known as aggressive fibromatosis, desmoid fibromatosis, and desmoid-type fibromatosis) are rare, locally invasive, soft tissue tumors that form in the connective tissues of the body. They can occur anywhere in the body. Common sites include the abdominal muscles, inside the abdomen, the head and neck area, trunk, breast, and the extremities.
Desmoid tumors do not have the ability to metastasize (i.e., spread through the blood or lymph system to other distant locations or organs), but in some rare cases, an individual can have more than one desmoid tumor (also called “multifocal”).1
Although desmoid tumors do not metastasize, they can be locally aggressive and severely damage surrounding tissues and vital structures as they grow. They also have a high rate of regrowth or “recurrence” after surgery, and should be monitored long-term in most cases.
For more information about diagnosis, treatment and pain management of desmoid tumors, patients and clinicians should consult the Global Consensus Paper published in the European Journal of Cancer (EJC) entitled “The management of desmoid tumours: A joint global consensus-based guideline approach for adult and paediatric patients.”
What causes desmoid tumors?
The majority of desmoid tumors occur spontaneously or randomly, meaning there is no clear cause or pre-existing condition related to the desmoid tumor. These “spontaneous” desmoid tumors often have a mutation in the beta-catenin (CTNNB1) gene. A mutation is a change in the DNA or “blueprint” of the gene. Importantly, in these cases, the mutant beta-catenin gene is only found in the desmoid tumor and is not present in the other cells of the body, is not inheritable, and cannot be passed to children.
On the other hand, approximately 5-10% of all desmoid tumor cases are related to a rare genetic condition known as familial adenomatous polyposis (F.A.P.), which is an inheritable condition that can run in families or be passed to children. F.A.P. is caused by a mutation in the APC gene that is present throughout all of the cells of the body.2 Individuals with F.A.P. have a higher risk of colon cancer than the general population, and may have inherited the APC gene, or could pass it along to children. The only way to know for sure if the desmoid tumor is related to F.A.P. is to have genetic testing through a blood test or cheek swab.
Signs and Symptoms
Symptoms from desmoid tumors vary greatly depending on the tumor location but can include pain, swelling, visible deformities, impact on mobility, and pressure on nearby organs affecting bodily functions such as urinary or bowel function, breathing, or swallowing. By contrast, some patients may have no symptoms at all and no visible physical manifestation of the tumor.
Learn more about diagnosis and the causes of desmoid tumors.
How are desmoid tumors classified? Are desmoid tumors cancer?
You will find that the medical community, articles and other sources will use differing terms when describing desmoid tumors. This can be confusing to patients as well as clinicians, and can lead to misunderstandings about treatment and minimize consideration of the potential serious consequences of the disease.
First, what is a “tumor?” A tumor is a non-specific term that simply means “a growth.” The word “tumor” does not imply anything about whether the growth is cancerous or non-cancerous.
Patients often ask, “Are desmoid tumors cancer?” The classifications set out by the World Health Organization (the “WHO”) for soft tissue tumors are the most decisive and descriptive on this question.3 The WHO classifies soft tissue tumors in the following four categories:
- intermediate (sometimes metastasizing),
- intermediate (locally aggressive) [desmoid tumors],
Malignant tumors spread to distant sites via the bloodstream or the lymphatic system. This spread is called metastasis. Desmoid tumors do not metastasize. For this reason, some sources will inaccurately use the simple term “benign” when referring to desmoid tumors, presumably because “benign” is a common medical term for a tumor that does not metastasize. However, the term benign does not take into account that desmoid tumors can cause destruction, functional problems, or pain in the area where they are growing. This is why the WHO categorizes desmoid tumors as “locally aggressive,” and the WHO guidelines go on to explain: “It is now broadly accepted that in between benign and malignant categories there exists an ‘intermediate’ category of lesions that can be locally aggressive,” and desmoid fibromatosis is classified in that intermediate category.3
It is important to note that desmoid tumors do not always behave aggressively. Some never cause symptoms, problems, or need to be treated.
LIVE: “What’s in a Name? ‘Cancer’ & Desmoid Tumors”
What kind of doctors treat desmoid tumors?
The doctors that specialize in desmoid tumors are sarcoma specialists, which is a group of oncologists with expertise in treating sarcomas. Sarcomas are rare types of cancers that form in the connective tissues in the body (for example, muscle, fat, blood vessels, bone, and cartilage). Because desmoid tumors also arise in connective tissues, they are within the purview of sarcoma specialists. Sarcoma specialists may consider treatments for desmoid tumors that are also used in sarcomas or other cancers (for example, chemotherapies, targeted therapies, local ablative or embolization techniques, and radiation therapy). As such, desmoid tumors may be referred to as “cancers” in some clinic documentation or insurance records so that the proper treatment is recognized and covered by insurance.
Patients are strongly encouraged to seek consultation and treatment from sarcoma specialists because they are most likely to be familiar with this rare disease and its recommended treatments.
To make a definitive diagnosis, a biopsy is performed to collect a sample of the tumor tissues and a pathologist will examine the tumor cells in a lab.
Learn more about diagnosis and the causes of desmoid tumors.
Treatment & Monitoring
Desmoid tumor cases can vary greatly. Treatment and monitoring is determined on an individual basis depending on location, size and symptoms.
Are Desmoid Tumors Considered Rare?
Yes, desmoid tumors are distinctly rare tumors, with an incidence of 5–6 cases per one million of the population per annum.3 A disease is generally considered “rare” when it affects fewer than 200,000 people in the United States. There are about 10,000 rare diseases. An estimated 25-30 million Americans are living with a rare disease.7 Desmoid tumors can occur in anybody of any age, with a peak age of 30-40 years.3 They are found more commonly in females compared to males (2:1).2
Given the rarity of this disease and lack of awareness outside of sarcoma specialists, desmoid tumors are often misdiagnosed, which can lead to improper clinical treatment. We highly recommend that you seek out a sarcoma specialist at a sarcoma center if you have been diagnosed with a desmoid tumor to ensure that you receive knowledgeable and appropriate care.
The DTRF also hosts an annual Patient Meeting where patients and their families can hear from multidisciplinary experts working in the field of desmoid tumors and their treatment. Learn more about the DTRF Together We Will Weekend.
Desmoid Tumors and Pregnancy
Researchers have determined that desmoid tumors are sometimes associated with pregnancy. These associations are not yet fully understood, and additional research is ongoing.
Every situation is different, and patients should discuss their pregnancy decisions with a sarcoma specialist. Recent research8 suggests that most desmoid tumor patients should not be counseled to avoid getting pregnant, or against carrying subsequent pregnancies after an initial desmoid tumor. However, tumor location, tumor growth rate, symptoms, recent treatment, and other factors should be considered in conversations with your specialist. It is important to be closely monitored during pregnancy by your care team since the rate of growth of the desmoid tumor may change during pregnancy. If you are considering becoming pregnant, please be sure to speak with your care team.
“What We’ve Learned from the International Pregnancy Study”
Recorded at the 2023 DTRF Patient Meeting
To find studies on desmoid tumors and pregnancy, please explore our Published Research.
A desmoid tumor diagnosis can leave you with uncertainty and questions. We’ve assembled a list of “first steps” to help you navigate this complex journey. One of the most important resources you’ll find there is the Global Consensus Paper on Desmoid Tumor Management, which provides information about the diagnosis, treatment and pain management of desmoid tumors.
Facts About Desmoid Tumors
900 - 1,500 cases Diagnosed Each Year
Desmoid tumors are rare.There are approximately 900 to 1,500 cases of desmoid tumors diagnosed in the United States every year.5
5 to 6 Out of 1 Million
Out of one million people, approximately five to six are diagnosed with desmoid tumors.2
The exact number of desmoid tumor cases is difficult to calculate due to inconsistent reporting and analyzing of clinical cases and frequent misdiagnosis.
Most Common in Ages 30s and 40s
Desmoid tumors tend to occur in younger adults in their 30s and 40s, but this disease can occur in anyone at any age.2
More common in Women
Desmoid tumors are seen 2 times more often in women than in men (2:1).6
Spontaneous regressions in 20% – 30% of Cases
Spontaneous regressions are observed in as many as 20%–30% of cases.2
First-line treatment Active Surveillance
Active surveillance is the accepted first-line treatment in most cases.
Second-line Treatment Surgery
Surgery is the accepted second-line treatment only for sporadic desmoid tumors located in the abdominal wall failing observation.2
For more information about diagnosis, treatment and pain management of desmoid tumors, please consult the Global Consensus Paper.
For someone newly diagnosed, these “First Steps” help you begin your journey from a place of knowledge and empowerment.
Our annual DTRF Together We Will Weekend is a time for patients, family, and friends to connect with each other and participate in informative lectures and roundtables on desmoid tumors and race/walk in our Running for Answers 5K.