Rhabdomyosarcoma


(rhabdo = rod, myo = muscle, sarcoma = cancer of the connective tissues)

The muscles of our body that move us, or allow us to pick up object are called skeletal muscles. Examples are the “quads”, “biceps” or “abs”. When looked at under a microscope, a biopsy of skeletal muscle looks like a rod. Rhabdo is greek for rod, myo means muscle, and sarcoma is the term for cancer of connective tissue so a rhabdomyosarcoma is cancer of the skeletal muscle.

Rhabdomyosarcoma is a rare cancer, but it’s the most common type of soft tissue cancer in kids with approximately 350 new cases per year in the U.S. There are subtypes (or categories) of rhabdomyosarcoma. The subtype, alveolar rhabdomyosarcoma, affects kids of all ages and is most often found in the arms, legs, and trunk. Embryonal rhabdomyosarcoma, develops in the muscles of the head, neck and genital area and is more common in children under 10 years.1,2.

Signs and Symptoms of Rhabdomyosarcoma

The symptoms of rhabdomyosarcoma depend on the location of the tumor. Alveolar rhabdomyosarcoma affects the muscles of the limbs and trunk and the pain associated with these tumors can be mistaken for a deep bruise or injury. The tumor can be very superficial (near the skin) so there may be a lump that doesn’t go away after a normal period of time. Other symptoms can include a general feeling of being tired or nauseated without a recognized reason.

Causes of Rhabdomyosarcoma

While there is no known cause of rhabdomyosarcoma, there are some conditions associated with this tumor. These include:

  • History of radiation therapy for treatment of another condition
  • Li-Fraumeni syndrome
  • Pleuropulmonary blastoma
  • Neurofibromatosis
  • Costello syndrome
  • Beckwith-Wiedemann syndrome
  • Noonan syndrome

Diagnostic Tests for Rhabdomyosarcoma

A soft tissue tumor may be initially suspected by a child’s pediatrician or by an emergency room physician when a child is seen for what is originally thought to be a muscle injury that isn’t healing. On physical exam there may be a lump that is considered to be abnormal. Further diagnostic testing is necessary to determine if this may be a soft tissue tumor process.

      MRI     An MRI enables the doctors to better see the full extent of a tumor. It is important to know if the tumor is ‘invading’ other tissues as treatment plans (such as surgical options) are being considered. It is also used to determine if there has been any spread of the tumor to the brain.
      Biopsy A biopsy is necessary to determine the exact type of tumor. It is important that the biopsy be done by a specialist experienced in appropriate biopsy of extremity tumors. A biopsy done incorrectly may limit surgical options, and in some cases make amputation the only surgical option.
  PET/CT scan This test is another that is necessary for staging of the cancer. It reveals if the cancer has metastasized to the abdomen, brain or other areas of the body

Rhabdomyosarcoma Grade

It is important to know how aggressive a tumor is (the grade of the tumor) as well as the stage of the cancer (has it spread to other area of the body). Because rhabdomyosarcoma is such an aggressive tumor it is always considered high grade.

Rhabdomyosarcoma Staging 2

Staging of any type of cancer involves determining if the cancer is only in the area where it was originally found (local) or if it has spread (metastasized). Knowing the stages helps the treating physicians determine the best treatment approach. Staging of rhabdomyosarcoma is a bit more complex than many other tumor types because it involves three different aspects of the tumor, including assessment of the tumor after it has been surgically removed (assuming it can be removed).

       First, the stage based on size of the tumor and if radiology tests (MRI, PET/CT) show the cancer has spread-

  • Stage I – the tumor is small and has not spread
  • Stage II or III – the tumor has spread to surrounding structures
  • Stage IV – the tumor has spread to other parts of the body

       Second, the disease is grouped based on if the cancer has spread and if all the cancer was removed by surgery –

  • Group I – all visible tumor is removed during surgery and the margins are negative; no spread to other areas.
  • Group II – all visible tumor is removed during surgery but the margins are positive; no spread to other areas.
  • Group III – all visible tumor could not be removed completely; tumor has spread to lymph but not to other organs.
  • Group IV – cancer has already shown signs of spreading to other organs at the time of diagnosis.

     

Risk group – by combining stage and group information, doctors can classify the child’s tumor into risk group based on how aggressive the tumor is. Assigning a risk group helps direct next treatment.

  • Low-risk – because rhabdomyosarcoma is such as aggressive tumor, no alveolar rhabdomyosarcoma falls into the low-risk group;
  • Intermediate-risk – includes kids with stage 1,2,or 3 disease
  • High-risk – includes kids with stage 4 disease

Treatment for Rhabdomyosarcoma

Removing the tumor is one of the most important aspects of treatment; therefore surgery is the first treatment considered for anyone diagnosed with rhabdomyosarcoma. Sometimes the tumor is in a location that it can be removed surgically, if this is the case then chemotherapy and/or radiation may be attempted with the goal of shrinking the tumor so it can be removed surgically.

Chemotherapy, or the use of medications, is necessary for anyone diagnosed with rhabdomyosarcoma. Ideally, chemo is started after the tumor has been removed. Chemo has been shown to decrease the chance that the tumor will return either to the area where it was first found or in other areas of the body. Radiation therapy, or the use of x-ray type energy, may be necessary if the entire tumor couldn’t be removed surgically. It may also be considered if the biopsy findings show that the tumor is a type that is extremely aggressive.

Prognosis of Rhabdomyosarcoma 4, 5

Prognosis, or chance of survival, is closely tied to the characteristics of the tumor – how large is it, how old is the child, where did the tumor start, and is it metastatic…all the information that goes into staging of the cancer. Often, the information that treating physicians have is the 5-year survival rate for a cancer type of a specific stage based on information from studies of a large number of people who were diagnosed with that type of cancer. The 5-year survival rate means the percentage of patients who live at least 5 years after their cancer is diagnosed. The general survival statistics based on risk group is:

  • Low-risk group
    5-year survival rate is over 90% for kids in the low-risk group.
  • Intermediate-risk group
    5-year survival rates range from about 60% to about 80% for kids in this group. The rate varies based on tumor location, stage, and the age of the child (children aged 1 to 9 tend to do better than older or younger children).
  • High-risk group
    5-year survival rate is generally around 20% to 40% because the kids in this group have metastatic disease at the time they are diagnosed. Children 1 to 9 years of age tend to have a better outlook than younger or older patients.

It’s important to remember that survival rates are at best rough estimates. A child’s unique circumstances also contribute to their response to the treatment and ultimately their prognosis.
 


References:

1. Ognjanovic S, Linabery AM, Charbonneau B, et al.: Trends in childhood rhabdomyosarcoma incidence and survival in the United States, 1975-2005. Cancer 115 (18): 4218-26, 2009
2. Gurney JG, Young JL Jr, Roffers SD, et al.: Soft tissue sarcomas. In: Ries LA, Smith MA, Gurney JG, et al., eds.: Cancer incidence and survival among children and adolescents: United States SEER Program 1975-1995. Bethesda, Md: National Cancer Institute, SEER Program, 1999. NIH Pub.No. 99-4649., pp 111-123
3. Lawrence W Jr, Anderson JR, Gehan EA, et al.: Pretreatment TNM staging of childhood rhabdomyosarcoma: a report of the Intergroup Rhabdomyosarcoma Study Group. Children's Cancer Study Group. Pediatric Oncology Group. Cancer 80 (6): 1165-70, 1997
4. Van Gaal JC, Van Der Graaf WT, Rikhof B, et al.: The impact of age on outcome of embryonal and alveolar rhabdomyosarcoma patients. A multicenter study. Anticancer Res 32 (10): 4485-97, 2012 5. Sultan I, Qaddoumi I, Yaser S, et al.: Comparing adult and pediatric rhabdomyosarcoma in the surveillance, epidemiology and end results program, 1973 to 2005: an analysis of 2,600 patients. J Clin Oncol 27 (20): 3391-7, 2009