Rhabdomyosarcoma is a rare cancer of the soft tissues, originating from cells that are supposed to develop into skeletal muscles. The resulting tumors are composed of rhabdomyoblasts, which are immature muscle cells that have not fully differentiated. Although it can occur at any age, rhabdomyosarcoma is the most common soft tissue cancer in children and adolescents. It can appear nearly anywhere but is most frequently found in the head, neck, urinary system, and reproductive organs.
Types of Rhabdomyosarcoma
Embryonal rhabdomyosarcoma (ERMS) is the most prevalent type, accounting for about 60% of cases, especially in young children. Its cells resemble the developing muscle cells of an early-stage embryo. ERMS commonly arises in the head, neck, or genitourinary tract. Subtypes include botryoid rhabdomyosarcoma, which presents as a grape-like mass, and spindle cell rhabdomyosarcoma. These embryonal forms of the cancer tend to respond well to treatment.
Alveolar rhabdomyosarcoma (ARMS) accounts for about 20-25% of cases and is more common in older children and teenagers. This form develops in the muscles of the arms, legs, or trunk. Its name comes from the tumor’s microscopic appearance, which resembles the alveoli of the lungs. ARMS is considered more aggressive than ERMS.
Less common types are more frequently seen in adults, such as pleomorphic rhabdomyosarcoma. This type primarily affects adults over 50, tends to form in the limbs, and is considered an aggressive form of the disease. The classification of the specific RMS type is a primary step that guides treatment decisions.
Signs, Symptoms, and Risk Factors
The signs and symptoms of rhabdomyosarcoma depend on the tumor’s size and location. A tumor near the surface of an arm or leg might present as a noticeable lump or swelling that may or may not be painful. Deeper tumors can cause symptoms by pressing on nearby tissues, nerves, or organs.
For example, a tumor in the head or neck can cause headaches, a bulging eye, or a droopy eyelid. Cancer in the abdomen or pelvis might lead to pain, vomiting, or constipation. Tumors affecting the urinary or reproductive systems can cause blood in the urine, difficulty with urination, or a vaginal mass. Bleeding from the nose, throat, or rectum can also be a symptom.
The exact cause of most cases is unknown, and the majority occur sporadically. However, certain inherited genetic syndromes are associated with an increased risk. These include Li-Fraumeni syndrome, which increases susceptibility to various cancers, and neurofibromatosis type 1 (NF1).
Other congenital conditions linked to RMS include Beckwith-Wiedemann syndrome, Costello syndrome, and DICER1 syndrome. These rare genetic disorders can increase the likelihood of certain tumors. While these syndromes elevate the risk, they do not guarantee that RMS will develop.
The Diagnostic Process
The diagnostic process begins with a physical examination and a review of the patient’s medical history. A healthcare provider will ask about symptoms and check for any lumps or other physical signs of a tumor. This evaluation guides the selection of further diagnostic tests.
Imaging studies like CT and MRI scans are used to visualize a potential tumor and determine its size and location. These scans provide detailed images of the body’s soft tissues, organs, and bones. A positron emission tomography (PET) scan may also be used to detect cancer cells throughout the body. Imaging techniques are also used to check if the cancer has spread.
A definitive diagnosis requires a biopsy, where a small tissue sample is surgically removed from the suspected tumor. A pathologist examines the tissue under a microscope to identify the cell type. Immunohistochemistry, a lab technique, helps confirm that the tumor is of skeletal muscle origin, which is the hallmark of RMS.
Once confirmed, the cancer is staged to determine its extent. Doctors use a system that considers the tumor’s size (T), spread to nearby lymph nodes (N), and metastasis to distant sites (M). A clinical group is also assigned based on how much tumor was removed during the initial surgery. This information is combined to assign a risk group (low, intermediate, or high) to guide the treatment plan.
Standard Treatment Modalities
Treatment for rhabdomyosarcoma involves a combination of therapies tailored to the patient. The plan depends on the RMS subtype, the tumor’s location and size, and the assigned risk group. This multi-modal approach aims to eliminate the cancer while minimizing long-term side effects.
Surgery is a common treatment, with the objective of removing as much of the tumor as possible. A complete resection, where the entire tumor is removed with a margin of healthy tissue, is the ideal outcome. The feasibility of surgery depends on the tumor’s location, as complete removal may not be possible if it is near organs or blood vessels.
Chemotherapy is a systemic treatment using drugs to kill cancer cells throughout the body. It is administered to nearly all RMS patients to shrink tumors before surgery, destroy remaining cancer cells after surgery, or treat cancer that has spread. Drug combinations, such as the VAC regimen (vincristine, actinomycin D, and cyclophosphamide), are often used in cycles.
Radiation therapy uses high-energy rays to destroy cancer cells in a specific area. It is often used after surgery to target any remaining cancer cells, reducing the chance of recurrence. Radiation may also be the primary treatment for tumors that cannot be surgically removed due to their location.
Factors Influencing Prognosis
Several clinical and biological factors influence the prognosis for an individual with rhabdomyosarcoma. These factors help medical teams predict the disease’s course and stratify patients into risk groups. This stratification helps in tailoring the intensity of therapy.
The tumor’s subtype is a significant factor. As noted earlier, patients with embryonal rhabdomyosarcoma (ERMS) have a more favorable prognosis compared to the more aggressive alveolar (ARMS) subtype. The presence of certain genetic changes, such as the PAX/FOXO1 fusion gene found in many ARMS cases, is also associated with the prognosis.
The location of the primary tumor also plays a role. Tumors that arise in “favorable” sites, such as the orbit of the eye or parts of the genitourinary tract, are often easier to treat effectively. This is in contrast to those in “unfavorable” sites like the limbs or the parameningeal region of the head. The tumor’s size at diagnosis is an additional consideration.
The patient’s age at the time of diagnosis can impact the outcome. A primary factor is whether the cancer has spread to distant parts of the body, a process known as metastasis. Patients with localized disease have a much better prognosis than those whose cancer has metastasized to areas like the lungs, bones, or bone marrow.