What is rhabdomyosarcoma (RMS)?
Childhood rhabdomyosarcoma (RMS) is a cancer arising within muscle cells and can be found throughout the body with the main site of tumor equally common in 1) head and neck 2) bladder, scrotum and vagina 3) limbs 4) other miscellaneous sites. With modern treatment programs using multiagent chemotherapy, surgery and radiation therapy, over two-third of children with RMS will be cured. Cure rates vary depending on the risk factors and your doctor will give you a better estimate after taking those all into account.
What are the signs of childhood RMS?
Typically RMS presents as a painless growing lump and the symptoms are related to where the tumor is located, e.g. involvement of the orbit of the eye may cause the eyeball to bulge out whereas RMS involving the base of the bladder causes difficulty in urination.
What causes RMS?
Nobody knows for sure, nothing in the diet or environment causes this. It not inherited, (except in rare genetic syndromes such as TP53 Li-Fraumeni syndrome and DICER1 mutations pleuropulmonary blastoma) so other children in the family should not be at risk.
How is RMS diagnosed?
Biopsy of the tumor (with removal of the whole tumor if possible) is the key test in which tumor tissue is removed by a surgeon and sent to a pathologist who reviews the cancer tissue under a microscope looking at the appearance of cancerous cells, and looking at markers on the surface of tumor cells, and doing special genetic tests which allows an accurate diagnosis and sub-type. Depending on the site of the tumor, the surgeon may also sample regional lymph nodes to check for tumor spread.
How is the likelihood of cure in RMS determined?
Before doing a biopsy a careful physical exam and history, and blood tests such as complete blood count (CBC), blood chemistry are done. Bilateral bone marrow aspirates and biopsies, in which liquid bone marrow and a tiny piece of bone is removed by inserting a needle into the hipbone while the child is sedated, can determine spread to the bone marrow. Imaging can help define the tumor and where it has spread, which will determine risk category and likelihood of cure.
- Chest x-ray.
- Computed tomography (CT) scan of the chest.
- CT scan of the abdomen and pelvis (for lower extremity or genitourinary tumors).
- Magnetic resonance imaging (MRI) of the skull/brain (for parameningeal tumors).
- PET-CT scan is a special kind of scan that can show where RMS has spread in the body (and later can also show whether it is responding to treatment).
- Bone scan
RMS is divided into two main types based on the appearance under the microscope:
- Embryonal: which constitutes two-thirds of cases, commonly seen in younger children, and usually with better outcomes.
- Alveolar: which constitutes less than one-third of cases, found equally in all childhood ages, but harder to cure. Alveolar RMS has a specific genetic abnormality in which two genes from different chromosomes are fused together (PAX3 or PAX7 and FOXO1), and testing for this can be helpful in confirming that a patient needs more intensive chemotherapy.
- Spindle cell/sclerosing: is rare, and in infants has gene rearrangements and fusions that are different from adults, with better outcomes.
Determining the risk category of RMS depends on multiple factors, so is complicated, but essentially takes into account the stage and group of the tumor, as seen in the table below.
- The stage ranks patients from 1 to 4 (1 being the best) based on:
- How large the tumor is and how far it has spread
- Whether the site of the tumor is favorable such as those listed below:
- Eye or area around the eye.
- Head or neck (but not near the ear, nose, sinuses, or base of the skull).
- Gallbladder and bile ducts.
- Ureter or urethra.
- Testes, ovary, vagina, or uterus
- Whether the tumor is embryonal, or lacks FOXO1 gene fusion, which is favorable
- The group ranks patients from I to IV (I being the best) based on:
- Whether the tumor was completely removed, or whether the surgeon had to leave small or large amounts behind