Embryonal rhabdomyosarcoma (ERMS) is a rare childhood cancer that arises from mesenchymal cells, the early form of muscle cells. It is a type of soft tissue sarcoma, a cancer of the body’s connective or supporting tissues. The name comes from its cellular resemblance to embryonic muscle.
ERMS is the most frequently diagnosed subtype of rhabdomyosarcoma, accounting for about 60-70% of all cases. It most often affects children under the age of five but can occur at any age. The tumors can develop anywhere in the body but are commonly found in the head and neck region and the genitourinary tract, including the bladder and prostate.
Causes and Symptoms
The precise cause of ERMS is largely unknown, and most cases are considered sporadic. Researchers have identified certain genetic changes that contribute to its development. These changes can sometimes be inherited, and ERMS is associated with a few rare genetic syndromes, including Li-Fraumeni syndrome, Beckwith-Wiedemann syndrome, and neurofibromatosis type 1.
Mutations in the RAS family of genes are also commonly found in ERMS tumors, which can drive tumor growth. While genetic factors play a role, lifestyle is not considered a major contributor to childhood cancers like ERMS. Exposure to X-rays before birth has been suggested as a possible risk factor, but the evidence is not conclusive.
Symptoms of ERMS depend on the tumor’s location, as the growth can press on surrounding tissues and organs. A common initial sign is a lump or swelling that may grow quickly but is often painless. Tumors in the head and neck can cause a droopy eyelid, bulging of the eye, persistent nasal congestion, or unexplained earaches.
If the tumor is in the genitourinary tract, a child might experience difficulty urinating, have blood in their urine, or have a noticeable mass in the vagina or on a testicle. For tumors in the abdomen or pelvis, symptoms can be more general, such as abdominal pain, constipation, or a palpable mass in the belly area.
The Diagnostic Process
Diagnosing ERMS begins with a physical examination and a review of the patient’s medical history. The doctor will ask about symptoms and feel for any lumps or swelling. This initial assessment helps guide subsequent diagnostic tests.
Imaging tests are then used to get a detailed look inside the body. Magnetic Resonance Imaging (MRI) is often preferred for children to limit radiation exposure and is particularly useful for defining tumors in the head and neck. Computed Tomography (CT) scans may also be used to assess the tumor and check if the cancer has spread to other areas, such as the lungs. A Positron Emission Tomography (PET) scan can help detect cancer cells throughout the body.
The definitive diagnosis is made through a biopsy, where a small sample of the tumor tissue is removed and examined under a microscope by a pathologist. In some instances, the surgeon may be able to remove the entire tumor during this procedure. The tissue sample is analyzed for specific characteristics and genetic markers to confirm an ERMS diagnosis.
The information gathered from all these tests is then combined to determine the cancer’s stage and to classify it into a risk group (low, intermediate, or high). This staging process assesses the tumor’s size, its location, and whether it has spread to other parts of the body, such as the lymph nodes or bone marrow.
Treatment Approaches
The treatment for embryonal rhabdomyosarcoma is a multi-modal approach, meaning it almost always involves a combination of therapies. The specific plan is tailored to the patient based on the tumor’s location and assigned risk group.
Chemotherapy is a primary treatment for nearly all patients with ERMS. It uses drugs to kill cancer cells, shrink the primary tumor, and eliminate any cancer cells that have spread. Even if surgery appears to have removed the entire tumor, chemotherapy is still used to address any microscopic cancer cells that might remain.
Surgery plays a significant role, with the goal of removing as much of the tumor as possible. Depending on the tumor’s size and location, surgery might be performed after a course of chemotherapy has been used to shrink the mass, making it easier to remove. In some cases, particularly for tumors in sensitive areas like near the eye, surgery may be limited to a biopsy.
Radiation therapy is another tool used to treat ERMS. It uses high-energy rays to destroy cancer cells left after surgery or when a tumor cannot be completely removed. Radiation is directed at the specific area where the tumor was located. For some patients, newer forms of radiation, like proton therapy, may be used to deliver radiation more precisely and reduce potential damage to surrounding healthy tissues.
Prognosis and Long-Term Follow-Up
The outlook for children with ERMS has improved substantially over the past several decades. The overall five-year survival rate for children with rhabdomyosarcoma is around 70%, but this figure can be much higher for ERMS, especially when it is localized. For localized ERMS, the 5-year survival rate can be as high as 90%.
Several factors identified during diagnosis and staging influence the prognosis. These include the tumor’s initial location, its size, the specific histologic subtype, and whether the cancer has spread to distant parts of the body at the time of diagnosis. Tumors located in more favorable sites, such as the orbit of the eye or parts of the genitourinary tract, have a better prognosis. The patient’s age at diagnosis also plays a part, with children between one and four years old often having the highest survival rates.
Life after treatment requires consistent and long-term follow-up care. Regular appointments are scheduled to monitor for any signs of the cancer returning, a process that often includes physical exams and imaging tests like chest X-rays and CT or MRI scans.
Follow-up care also focuses on managing potential long-term side effects of treatment, known as late effects. These can vary depending on the specific treatments received but may include issues related to growth and development, fertility, or the function of certain organs. There is also a small risk of developing a second cancer later in life, making ongoing medical supervision a part of survivorship.