Alveolar rhabdomyosarcoma

Alveolar rhabdomyosarcoma (ARMS) is a rare and aggressive soft tissue cancer that arises from skeletal muscle precursor cells (rhabdomyoblasts). It is one of the two major subtypes of rhabdomyosarcoma, the other being embryonal rhabdomyosarcoma. The name 'alveolar' refers to the microscopic appearance of the tumor, which resembles the small air sacs (alveoli) of the lung, though the tumor itself does not originate in the lungs. ARMS most commonly affects children, adolescents, and young adults, and tends to occur in the extremities, trunk, and periorbital region, though it can arise in virtually any anatomical site. It is characterized by specific chromosomal translocations, most commonly t(2;13)(q35;q14) involving the PAX3-FOXO1 fusion gene, or less frequently t(1;13)(p36;q14) involving PAX7-FOXO1. These fusion-positive tumors are associated with a more aggressive clinical course. Key symptoms depend on the tumor's location but commonly include a rapidly growing mass or swelling, pain at the tumor site, and signs related to compression or invasion of nearby structures. When occurring in the extremities, patients may notice a firm, enlarging lump. Tumors in the head and neck region can cause proptosis (bulging of the eye), nasal obstruction, or cranial nerve palsies. ARMS has a higher tendency to metastasize compared to embryonal rhabdomyosarcoma, with common sites of spread including the lungs, bone marrow, bones, and lymph nodes. Systemic symptoms such as fatigue and weight loss may occur with advanced disease. Treatment for alveolar rhabdomyosarcoma typically involves a multimodal approach combining chemotherapy, surgery, and radiation therapy. Standard chemotherapy regimens generally include vincristine, actinomycin D, and cyclophosphamide (VAC protocol), often with the addition of other agents such as irinotecan and doxorubicin for higher-risk patients. Surgical resection is performed when feasible, and radiation therapy is used for local control. Despite aggressive treatment, the prognosis for ARMS, particularly fusion-positive disease, remains less favorable than for embryonal rhabdomyosarcoma, especially in patients with metastatic disease at diagnosis. Ongoing clinical trials are investigating targeted therapies and immunotherapeutic approaches to improve outcomes.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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