Alveolar rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) is a rare and aggressive type of rhabdomyosarcoma, a cancer that arises from skeletal muscle tissue. It primarily affects children and adolescents, although it can occur at any age. ARMS is characterized by the presence of small, round cells that resemble the alveoli of the lungs, hence the name "alveolar."

Classification

Alveolar rhabdomyosarcoma is classified under the broader category of soft tissue sarcomas. It is one of the two main subtypes of rhabdomyosarcoma, the other being embryonal rhabdomyosarcoma (ERMS). ARMS is further divided into two subtypes based on genetic characteristics:

• PAX3-FOXO1 positive ARMS
• PAX7-FOXO1 positive ARMS

Pathophysiology

The hallmark of ARMS is the presence of specific chromosomal translocations, most commonly t(2;13)(q35;q14) and t(1;13)(p36;q14), which result in the fusion of the PAX3 or PAX7 genes with the FOXO1 gene. These genetic alterations lead to the production of abnormal fusion proteins that drive the malignant transformation of muscle cells.

Clinical Presentation

Patients with alveolar rhabdomyosarcoma typically present with a rapidly growing mass, which may be painful. The tumor can occur in various locations, including the extremities, trunk, and head and neck region. Symptoms depend on the tumor's location and may include:

• Swelling or a lump
• Pain or tenderness
• Functional impairment of the affected area

Diagnosis

The diagnosis of ARMS involves a combination of clinical evaluation, imaging studies, and biopsy. Histopathology and immunohistochemistry are essential for confirming the diagnosis. Commonly used markers include myogenin and desmin. Molecular testing for the characteristic PAX-FOXO1 fusion genes is also crucial for diagnosis.

Treatment

The treatment of alveolar rhabdomyosarcoma typically involves a multimodal approach, including:

• Surgery: To remove the tumor when feasible.
• Chemotherapy: Often includes agents such as vincristine, dactinomycin, and cyclophosphamide.
• Radiation therapy: Used to target residual disease post-surgery or for inoperable tumors.

Prognosis

The prognosis for patients with ARMS is generally poorer compared to those with ERMS, largely due to its aggressive nature and higher likelihood of metastasis. Factors influencing prognosis include the tumor's size, location, and the presence of metastases at diagnosis.

Research and Future Directions

Ongoing research aims to better understand the molecular mechanisms underlying ARMS and to develop targeted therapies. Clinical trials are exploring new treatment options, including immunotherapy and targeted therapy.

See Also

• Rhabdomyosarcoma
• Soft tissue sarcoma
• Pediatric oncology