Desmoid tumor

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

A desmoid tumor is an abnormal growth that arises from connective tissue, which is the tissue that provides strength and flexibility to structures such as bones, ligaments, and muscles. Affected individuals typically develop a single tumor, although some have multiple tumors. Desmoid tumors most often develop when people are in their 30s or 40s, although they can occur anytime between adolescence and late adulthood.

Tumors that form in the abdomen or abdominal wall are called abdominal desmoid tumors, those that arise from the tissue that connects the abdominal organs are called intra-abdominal desmoid tumors, and tumors found in other regions of the body are called extra-abdominal desmoid tumors. Extra-abdominal tumors occur most often in the shoulders, upper arms, and upper legs.

Desmoid tumors are fibrous, much like scar tissue. They are generally noncancerous (benign) because they do not spread to other parts of the body (metastasize); however, they can aggressively invade the surrounding tissue and can be very difficult to remove surgically. Desmoid tumors can recur, even after they are removed. In about 20 percent of cases, the tumors shrink or disappear with minimal or no treatment (spontaneously regress).

Desmoid tumors may not cause any signs or symptoms. When they do cause symptoms, the most common one is pain. The pain is often due to the tumor pressing against nearby organs, tissues, or blood vessels. Other signs and symptoms are often caused by growth of the tumor into the surrounding tissue, and they can vary based on the size and location of the tumor. Intra-abdominal desmoid tumors can block the bowel, causing constipation. Extra-abdominal desmoid tumors can restrict the movement of affected joints, making it difficult to move the arms or legs.

Desmoid tumors can also occur in combination with other conditions. Desmoid tumors are found in 10 to 30 percent of people with an inherited form of colon cancer called familial adenomatous polyposis (FAP). These individuals typically develop intra-abdominal desmoid tumors in addition to abnormal growths (called polyps) and cancerous tumors in the colon. Desmoid tumors that are not part of FAP are described as sporadic.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also called mutations) in the CTNNB1 gene account for around 90 percent of sporadic desmoid tumors. Variants in the APC gene cause the desmoid tumors that are associated with FAP. Both genes are involved in an important cell signaling pathway that controls the growth and division (proliferation) of cells and the process by which cells mature to carry out specific functions (differentiation).

The CTNNB1 gene provides instructions for making a protein called beta-catenin. This protein interacts with other proteins to control the activity (expression) of particular genes, which helps promote cell proliferation and differentiation. CTNNB1 gene variants lead to an abnormally stable beta-catenin protein that is not broken down when it is no longer needed. The protein accumulates in cells, where it continues to function and allows uncontrolled cell proliferation and the formation of desmoid tumors.

The protein produced from the APC gene helps regulate the levels of beta-catenin in the cell by attaching (binding) to other proteins to form a complex. When this complex binds to beta-catenin, it helps to break down the protein. Variants in the APC gene cause cells to produce an abnormally short version of the APC protein that is unable to form the complex. As a result, beta-catenin is not broken down and, instead, accumulates in cells. Excess beta-catenin promotes uncontrolled growth and division of cells, causing the formation of polyps and, occasionally, desmoid tumors in people with FAP.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Most desmoid tumors are not inherited. These tumors are caused by variants in genes that occur during a person's lifetime, called somatic variants. Somatic variants in the CTNNB1 gene can cause sporadic desmoid tumors. A somatic variant in one copy of the gene is sufficient to cause the disorder.

An inherited variant in one copy of the APC gene causes FAP and predisposes affected individuals to develop desmoid tumors. FAP is inherited in an autosomal dominant pattern, which means one copy of the altered APC gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one parent with the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Desmoid tumors are rare, affecting an estimated 2 to 6 per 1 million people worldwide. In the United States, about 1,000 new cases are diagnosed per year. About 10 percent of all desmoid tumors occur in people with FAP. For reasons that are unclear, women develop desmoid tumors more often than men with women accounting for 70 percent of cases.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of the abdominal wall · Very frequent (99-80%)

The presence of any abnormality affecting the abdominal wall.

Abnormality of the musculature · Very frequent (99-80%)

Abnormality originating in one or more muscles, i.e., of the set of muscles of body.

Desmoid tumors · Very frequent (99-80%)

Benign, slow-growing tumors without any metastatic potential. Despite their benign nature, they can damage nearby structures causing organ dysfunction. Histologically they resemble low-grade fibrosarcomas, but they are very locally aggressive and tend to recur even after complete resection. There is a tendency for recurrence in the setting of prior surgery and the most common localisation of these tumors is intraabdominal from smooth muscle cells of the instestine.

Fibroma · Very frequent (99-80%)

Benign tumors that are composed of fibrous or connective tissue. They can grow in all organs, arising from mesenchyme tissue. The term "fibroblastic" or "fibromatous" is used to describe tumors of the fibrous connective tissue. When the term fibroma is used without modifier, it is usually considered benign, with the term fibrosarcoma reserved for malignant tumors.

Subcutaneous nodule · Very frequent (99-80%)

Slightly elevated lesions on or in the skin with a diameter of over 5 mm.

Abdominal pain · Frequent (79-30%)

An unpleasant sensation characterized by physical discomfort (such as pricking, throbbing, or aching) and perceived to originate in the abdomen.

Abnormality of retinal pigmentation · Frequent (79-30%)

Any deviation from the normal pigmentation of the retina.

Intestinal polyposis · Frequent (79-30%)

The presence of multiple polyps in the intestine.

Other findings in the same source

From: Orphanet

Additional reported features include Malabsorption (Frequent (79-30%)); Myalgia (Frequent (79-30%)); Abnormality of the upper urinary tract (Occasional (29-5%)); Arthralgia (Occasional (29-5%)); Chest pain (Occasional (29-5%)); Gastrointestinal hemorrhage (Occasional (29-5%)); Hydronephrosis (Occasional (29-5%)); Intestinal obstruction (Occasional (29-5%)); Limitation of joint mobility (Occasional (29-5%)); Neoplasm of the skin (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Desmoid tumor is Oncology, with a oncologist and relevant organ specialist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics; Relevant organ specialist / Surgical Oncology as indicated.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Has the exact tumour type been confirmed, and is staging relevant?
• What is the goal of each proposed treatment option?
• How will side effects, daily function and supportive care be addressed?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.