Alveolar rhabdomyosarcoma is the subtype of rhabdomyosarcoma, which resembles tissues of the lung (alveoli).
Rhabdomyosarcoma is a soft tissue tumor,which most often occur in children and adolescents. Rarely, it is seen in adults over 40. Common sites where rhabdomyoma develops are head and neck (40%), genitourinary tract (20%), retroperitoneual cavity and the limbs. The tumor arises from mesenchymal cells (the precursors of skeletal muscles), that don’t differentiate normally.
Alveolar rhabdomyosacomas are common for a bit older individuals. The most common age of the diagnosis is 10-25 years.
There are several types of rhabdomyosarcoma distinguished:
- alveolar, which comprises 20-40% of all rhabdomyosarcomas;
- embryonal, which comprises 60% of cases;
- anaplastic rhabdomyosarcoma.
In alveolar rhabdomyosarcoma the translocation between the FKHR/FOXO1 transcription factor gene (on chromosome 13) and either PAX3 transcription factor gene (on chromosome 2) or PAX7 gene (on chromosome 1) may be identified, mutations of N‐MYC, ALK and MET genes may also be present.
Both alveolar and embryonal subtypes are characterized by the over‐expression of insulin growth factor 2 (IGF‐2).
See also: Myeloblastic leukemia
Alveolar rhabdomyosarcoma usually arises in the deep parts of the extremities, although it may be found anywhere in the body.
Common symptoms of rhabdomyosarcoma are the swelling/painful palpable mass at the site of origin along with other local symptoms – displacement of the eye, vaginal bleeding, dysuria, etc.
Rhabdomyosarcoma of the head and neck may be suspected when the following symptoms are present: diplopia (doubled vision), exophtalmos (bulging of the eyeball), headache, congestion, nasal discharge, cranial nerve palsy, dysphagia, hearing or vision loss. Genitourinary rhabdomyosarcoma may cause urinary tract obstruction or constipation. Abdominal or pelvic manifestations include abdominal pain and abdominal mass, ascites, haematuria.
On biopsy the tumor appears as an accumulation of low differentiated cells, round or oval, with multiple areas of necrosis and irregular spaces that remind alveoli.
The diagnosis is made based on:
- Radiographic imaging of the site of origin, chest X-ray;
- CT of the chest, tumor site;
- MRI of the tumor site;
- Total body bone scan;
- Biopsy of the lesion;
- Bone marrow biopsy;
- Lumbar puncture (only for parameningeal RMS)
Treatment depends on the size of the tumor, its location and spread. Surgery solely is used when the tumor is localized. The combination of surgery, chemotherapy, radiotherapy and immunotherapy is usually used.
Chemotherapy agents which are used in the treatment of rhabdomyosarcoma include:
- actinomycin D;
Alveolar rhabdomyosarcomas tend to have worse prognosis than other types of the tumor.
In general the survival rate is 70-75%. The five-year survival rate for low-risk is 95%, intermediate-risk – 65% and high risk – 15%.