Desmoid fibromatosis is a rare soft tissue neoplasm that does not metastasize but presents an aggressive growth and local invasion (1). It can affect all age groups and occur throughout the body (1, 2). In children, there is limited information on managing these complex tumors. We present the case of a young boy in whom a rapidly growing mass was detected in his chest. Desmoid fibromatosis was the final diagnosis.

DF is an extremely infrequent tumor (2 to 4 cases per million per year) (1, 2). It's categorized as a slowly growing borderline tumor with low malignant potential formed by the monoclonal proliferation of fibroblasts in muscles, tendons, and ligaments (2, 3). This proliferation can lead to local aggressiveness that, depending on its location, can severely affect or impair vital organs, leading to functional impairment and life-threatening conditions (1, 3). Although the pathological pathways are still under investigation, DF is believed to appear from the mesenchymal stromal cells with mutation of the CTNNB1 gene in adults (the β-catenin gene) (1, 4). In children, it's associated with AKT (31%), BRAF (19%), and p53 (9%) mutations, in addition to the CTNNB1 (3–5).

DF can present in two ways; the sporadic form, which more frequently affects women, and the condition associated with familial adenomatous polyposis (FAP) (1, 6). DF clinically appears as a firm, often asymptomatic, slow-growing mass (2, 3). Its course can be indolent (5 to 10% of the cases) or invade nearby structures (3, 4). In children, DF primarily affects the head and neck (1). In adults, the trunk and limbs are more affected (1, 2). In our case, the patient presented with a mass that affected his thoracic wall. Treatment will depend on the course of the tumor; a conservative approach or “watch-and-wait” strategy has been suggested if the tumor doesn't show progression (6, 7). However, surgery is recommended if the tumor is over 5 cm, located in the head or neck, and affects younger patients (<10 years) (3, 5). As we did in our case.

Treatment will be based on the symptoms and the tumor growth, especially in critical locations where an earlier surgical decision may potentially prevent a higher risk of morbidity (9). The primary goal should be a wide (R0) microscopic margin resection; however, in problematic locations like the skull base or when functions or cosmetics is an issue, positive (R1), microscopic margins can also be accepted (8–10). Treatment options other than surgery may be preferred when positive microscopic margins are found (10). If an R1 resection is achieved after the initial surgery, in that case, neither perioperative radiotherapy nor reoperation is necessarily required since the risk of a local recurrence when we compare surgery alone and perioperative radiotherapy is not statistically significantly different (11). In contrast, the morbidity of the two combined modalities is higher (10, 11).

Even with successful surgery the risk of relapse is high especially in children where pediatric DF is associated with a high recurrence rate (24%–76%) (5, 6). Therefore, other treatments have also been proposed (8, 9). Another thing to consider is reconstruction in pediatric patients, as children have unique characteristics related to growth; therefore, the prosthetic material for reconstruction should be chosen carefully. Bioabsorbable materials should be used to avoid complications (8, 9). Since these materials were not available to us, we had to use rigid fixation.

Other therapies include radiation therapy as an adjuvant treatment; however, the risk of adverse effects, such as fibrosis, paresthesia, skin ulcers, and, in children, a significant risk of long-term functional sequelae and radiation-induced cancers, must be taken into account. Several cytotoxic and non-cytotoxic drug treatments have been proposed for desmoid tumors, and several have had partial or complete responses in multiple trials (11, 12). Newer treatments, such as tyrosine kinase inhibitors of vascular endothelial growth factor receptors, have also arisen as potential therapies in the future (6, 7). However, each case must be individualized. In our case, surgery was completed as the mass had aggressive behavior, but we could not achieve negative margins; therefore, even though radiotherapy, chemotherapy, anti-hormonal therapies, and tyrosine kinase inhibitors were considered. After exposing all the treatments with their benefits and risk to the child's parents, and multiple discussions with a pediatric oncologist, surveillance was decided.

When facing a desmoid tumor and its treatment, especially in pediatric patients, there are still many gray areas between surgery, observation, and medical therapies. Deciding between them is not always easy, as we should always avoid or limit any possible harm from the disease and our treatments. Still, quality of life must be the single central dimension to weigh when facing these tumors, a decision that must always be made following the wishes of the parents and the child. This article has been prepared according to CARE Guidelines (13).

His parents found it difficult at first to accept the disease, especially after the pathology and the positive margins of the tumor were explained to them. However, after the patient's successful recovery and normal development, they have come to accept its nature. They have changed their approach and have learned to accept the nature of the disease in a way that has surprised the entire medical team. We are grateful to the parents for allowing us to treat the patient, and we are on close watch.

The management of DF is complex and even with treatment, it can still behave like an aggressive disease. Further research is needed to determine which patients will benefit from surgery, medical therapies, or close surveillance. We will always have to weigh the risk of treating the disease with all the complications and recurrences that it entails or waiting and losing the opportunity to offer a chance of a complete cure.