Desmoid fibromatosis is a rare and often misunderstood soft tissue tumor. While not cancerous, it can behave aggressively within the body. This article clarifies its nature, causes, diagnosis, and treatment approaches.
Understanding Desmoid Fibromatosis
Desmoid fibromatosis, also known as aggressive fibromatosis, is a rare type of tumor that originates from connective tissue cells called fibroblasts. While these tumors are considered non-cancerous, meaning they do not spread to distant parts of the body, they are locally aggressive. This local aggressiveness means they can grow into and infiltrate surrounding tissues and organs, potentially causing significant problems.
These tumors can develop almost anywhere in the body where connective tissue is present. However, they commonly appear in locations such as the abdominal wall, inside the abdomen (particularly the mesentery), the limbs, and the chest wall. The World Health Organization reclassified desmoid tumors in 2020 as an intermediate, locally aggressive fibroblastic and myofibroblastic tumor, reflecting their infiltrative nature and tendency to recur even after removal.
Causes and Risk Factors
The exact cause of desmoid fibromatosis is often unknown, and most cases occur sporadically without a clear inherited cause. Approximately 85% of these sporadic tumors involve a mutation in the CTNNB1 gene, which affects the beta-catenin pathway. However, a smaller proportion, about 5% to 10% of desmoid tumor cases, are linked to a genetic condition called familial adenomatous polyposis (FAP) syndrome. These FAP-associated tumors are caused by mutations in the APC gene and are more commonly found within the abdomen.
Trauma or previous surgery to an area has been identified as a potential trigger. Hormonal influences also play a role; desmoid tumors are more common in women, especially during or after pregnancy, and can be associated with oral contraceptive use. This suggests a connection to high estrogen states, as tumors can sometimes regress with menopause, and anti-estrogen therapies have been explored.
How Desmoid Fibromatosis is Diagnosed
The diagnostic process for desmoid fibromatosis often begins when an individual notices a palpable lump, experiences pain, or the tumor is incidentally found during imaging for another reason. Imaging techniques are important for identifying the tumor and assessing its extent. Magnetic Resonance Imaging (MRI) is generally the preferred method due to its superior soft tissue contrast, allowing better visualization of the tumor against surrounding tissues. Computed tomography (CT) scans and ultrasound can also be used, providing additional clues about the tumor’s size and location.
A definitive diagnosis requires a biopsy, where a tissue sample is removed from the tumor and examined under a microscope by a pathologist. Molecular testing is often performed on the biopsy sample to identify specific genetic mutations, such as those in the CTNNB1 or APC genes, which can confirm the diagnosis and inform treatment strategies.
Treatment Options
Treatment for desmoid fibromatosis is highly individualized due to the unpredictable nature of these tumors. For asymptomatic or slow-growing tumors, a “watchful waiting” approach, also known as active surveillance, is often the initial recommendation. This involves regular monitoring with imaging scans, as some desmoid tumors can remain stable or even shrink on their own.
Surgical removal of the tumor, or resection, was historically a primary treatment, but it is now often considered a second-line option due to challenges in achieving clear margins and a high recurrence rate. Recurrence rates after surgery can range from 25% to 60%, even with seemingly complete removal, because the tumors can have microscopic tendrils that extend into surrounding tissues. When surgery is not feasible or carries significant risks, or if the tumor is rapidly growing, non-surgical systemic therapies may be used.
These systemic treatments include chemotherapy, with doxorubicin-based regimens showing some success. Targeted therapies, such such as tyrosine kinase inhibitors (e.g., sorafenib, imatinib, pazopanib), work by blocking growth signals within the tumor cells. Non-steroidal anti-inflammatory drugs (NSAIDs) can help manage symptoms and may contribute to tumor regression. Hormonal therapies, like tamoxifen, are also an option, particularly for abdominal wall tumors, given the potential influence of hormones on tumor growth. Radiation therapy can be considered as an alternative for tumors difficult to remove surgically or as an adjuvant treatment after surgery. Treatment decisions are typically made by a multidisciplinary team of specialists to tailor the approach to each patient’s unique situation.
Long-Term Outlook and Management
The long-term course of desmoid fibromatosis is often unpredictable. Some tumors may remain stable or even spontaneously regress over time, while others may continue to grow. Despite treatment, there is a recognized high local recurrence rate, especially after surgical interventions. This necessitates ongoing monitoring, often through regular imaging such as MRI or CT scans, typically every few months, to detect any changes or regrowth.
While desmoid tumors are rarely life-threatening because they do not metastasize, their local aggressiveness can significantly impact a person’s quality of life. They can cause pain, swelling, and restrict movement, depending on their location. Comprehensive care may involve not only medical management but also pain management strategies, physical therapy to maintain function, and psychological support to help individuals cope with the chronic and unpredictable nature of the condition.