Alveolar rhabdomyosarcoma is a rare and aggressive soft tissue sarcoma that develops from immature muscle cells, primarily affecting children, adolescents, and young adults. This cancer most commonly arises in the large muscles of the torso, arms, and legs. The term “alveolar” describes the microscopic appearance of the cancer cells, which resemble the air sacs (alveoli) of the lungs. This name refers only to the cellular structure and does not indicate a connection to the lungs unless the cancer originates or spreads there.
Genetic Causes and Risk Factors
The development of alveolar rhabdomyosarcoma is linked to specific genetic abnormalities within the cancer cells. The most common cause is a chromosomal translocation, a process where pieces of two different chromosomes break off and switch places. This event creates an abnormal “fusion gene” that disrupts cell function and drives cancerous growth. In most cases, this involves the fusion of either the PAX3 or PAX7 gene with the FOXO1 gene.
These genetic changes are sporadic, meaning they happen randomly in a single cell and are not inherited. Researchers have not identified what causes these specific translocations to occur. Consequently, there are no known environmental or lifestyle factors that increase the risk of developing this cancer.
Recognizing Signs and Symptoms
The signs and symptoms of alveolar rhabdomyosarcoma depend on the tumor’s location and size, so its physical manifestations are diverse. The first indication is often a persistent lump or swelling that may or may not be painful. This presentation is common for tumors located in the muscles of the arms or legs.
When a tumor forms in other locations, symptoms reflect the structures being affected. For example, a tumor in the head and neck region can lead to persistent nasal congestion, nosebleeds, or vision changes. If the cancer develops near the spine, it might press on nerves, causing weakness or pain in the limbs. Tumors in the abdomen or pelvis can result in constipation or difficulty urinating as they compress nearby organs.
The Diagnostic Process
The diagnostic process begins with a physical examination and a review of the patient’s medical history. Following this, imaging studies are ordered to visualize the mass and determine its size and location. These imaging tests include magnetic resonance imaging (MRI) and computed tomography (CT) scans. A positron emission tomography (PET) scan may also be used to check if the cancer has spread.
While imaging provides valuable information, a definitive diagnosis requires a biopsy. During this procedure, a surgeon removes a small tissue sample from the tumor. This tissue is sent to a pathologist for microscopic examination to identify the cancerous cells and confirm they are characteristic of rhabdomyosarcoma.
The final step is to differentiate the alveolar subtype from other forms of rhabdomyosarcoma. This is accomplished through molecular testing on the biopsy sample, which looks for the genetic translocation that creates the PAX-FOXO1 fusion gene. The presence of this fusion gene confirms the diagnosis and provides information for determining the treatment strategy and prognosis.
Multimodal Treatment Approaches
Treatment for alveolar rhabdomyosarcoma is intensive and involves a combination of therapies, known as a multimodal approach. The plan is customized based on the patient’s age, the tumor’s location and size, and whether the cancer has spread. The primary treatment for most patients is chemotherapy. This systemic therapy uses drugs to shrink the primary tumor and eliminate cancer cells that may have traveled to other areas of the body.
Radiation therapy is a frequent component of the treatment plan. It uses high-energy beams to target the original tumor site, achieving local control by destroying any cancer cells that might remain. Radiation may be administered before or after other interventions, and its goal is to reduce the risk of the cancer returning in the same location.
Surgery to remove the tumor is another component of treatment, though its feasibility depends on the tumor’s location and proximity to important structures. In some cases, chemotherapy and radiation are used first to shrink the tumor, making it safer for surgeons to remove it completely. A team of specialists coordinates these three modalities to provide the most effective action for each patient.
Prognosis and Long-Term Follow-Up
The outlook for an individual with alveolar rhabdomyosarcoma is influenced by several factors. The cancer’s stage at diagnosis, which indicates whether it is localized or has spread, is a significant consideration. Other factors include the patient’s age, the primary tumor’s location, and the molecular profile of the tumor, specifically the presence of the PAX-FOXO1 gene fusion.
Following the completion of treatment, long-term follow-up care is necessary. This involves a regular schedule of monitoring to watch for any signs of cancer recurrence. This surveillance includes periodic imaging scans of the original tumor site and other areas of the body.
This long-term care also focuses on managing potential late effects from treatment. Chemotherapy and radiation can cause side effects that may not appear until months or years after treatment has ended. These can include issues with growth, organ function, or the development of secondary cancers. The follow-up plan is designed to detect and address these potential complications early.