Infantile fibrosarcoma (IFS) is a rare soft tissue cancer primarily affecting infants and young children. This malignant tumor originates in the fibrous connective tissues throughout the body. While it is considered a cancerous growth, it generally has a more favorable prognosis compared to fibrosarcomas seen in older children and adults.
Understanding Infantile Fibrosarcoma
Infantile fibrosarcoma develops from mesenchymal cells, which give rise to connective tissues like fat, muscles, tendons, nerves, and blood vessels. It often presents as a rapidly growing mass, sometimes exceeding 15 cm in diameter. These tumors are most frequently found in the extremities, but they can also appear in the trunk, head, or neck.
A distinguishing feature of infantile fibrosarcoma is the ETV6-NTRK3 gene fusion. This fusion results from a chromosomal rearrangement where parts of the ETV6 gene on chromosome 12 and the NTRK3 gene on chromosome 15 combine. This genetic hallmark helps differentiate IFS from adult fibrosarcoma, which behaves more aggressively and lacks this fusion.
Identifying and Diagnosing Infantile Fibrosarcoma
Identification of infantile fibrosarcoma often begins with a noticeable lump or swelling, which may be painless. The skin over the tumor may appear discolored or feel warm to the touch. Depending on the tumor’s location, symptoms might also include pain, soreness due to compressed nerves or muscles, or difficulty using an affected limb.
The diagnostic process involves a physical examination followed by imaging studies. Magnetic Resonance Imaging (MRI) assesses the tumor’s size, exact location, and its relationship to surrounding tissues, nerves, and blood vessels. Computed Tomography (CT) scans may also be used to evaluate bone involvement or check for potential spread.
A biopsy is a definitive diagnostic step, where a tissue sample is obtained from the tumor, either through a needle or an open surgical procedure. This tissue is then examined by a pathologist to confirm cancerous cells and determine the sarcoma type. Genetic testing on the biopsy sample for the ETV6-NTRK3 fusion gene confirms the diagnosis of infantile fibrosarcoma.
Treatment Strategies
Treatment for infantile fibrosarcoma is tailored to each child and involves a team of specialists. Surgery is the primary treatment approach, aiming for complete removal of the tumor along with a margin of healthy surrounding tissue to reduce the risk of recurrence. However, due to the tumor’s size or location, complete surgical removal might not always be feasible initially.
Chemotherapy may be used with surgery. It can be administered before surgery (neoadjuvant chemotherapy) to shrink the tumor, potentially making it easier to remove or allowing for a less extensive procedure. Chemotherapy might also be given after surgery (adjuvant chemotherapy) to eliminate any remaining cancer cells. While traditional chemotherapy agents like vincristine, actinomycin, and cyclophosphamide can be effective, they may carry side effects such as bone marrow suppression.
Targeted therapies, specifically NTRK inhibitors like larotrectinib, show promise for tumors with the ETV6-NTRK3 gene fusion. These inhibitors work by blocking the abnormal protein produced by the gene fusion, which drives tumor growth. Larotrectinib has demonstrated rapid and significant tumor shrinkage, potentially allowing for less invasive surgery or even avoiding it. Radiation therapy is typically avoided in infants due to potential long-term side effects on developing tissues, but it may be considered when complete surgical removal is not possible or recurrence is high.
Prognosis and Follow-Up Care
Infantile fibrosarcoma carries a favorable prognosis compared to other soft tissue sarcomas, with high survival rates. Studies indicate that over 80% to 90% of patients are cured, with a 10-year survival rate of 90%. The outlook is particularly good when the tumor can be completely removed through surgery.
Several factors can influence the prognosis, including the tumor’s size, location, and whether surgical removal was complete. Tumors located in the limbs tend to have a better prognosis than those in the trunk or head and neck. Although the risk of metastasis (spread to other parts of the body) is low, it can occur, typically to the lungs.
Long-term follow-up care is important for children who have been treated for infantile fibrosarcoma. This care includes regular clinical evaluations and imaging studies, such as MRI or CT scans, to monitor for any signs of tumor recurrence. Ongoing monitoring also helps manage any potential long-term effects from treatment.