Sclerosing Rhabdomyosarcoma
Definition
- Rhabdomyosarcoma with a densely sclerotic background stroma.
Diagnostic Criteria
- Neoplastic cells set in a densely hyalinized eosinophilic background stroma
- Arranged in nests, microalveoli or cords
- May produce a pseudovascular pattern
- Composed of small undifferentiated cells
- Giant cells or myoblasts are rare
- Anaplastic cellular features may be seen in approximately 13% of all subtypes of rhabdomyosarcoma.
- Anaplasia is defined as neoplastic nuclei at least 3 times the size of their neoplastic neighbors and/or atypical mitotic figures.
- If present, the focal or diffuse nature of the anaplasia should also be described.
- Focal anaplasia refers to anaplastic cells loosely scattered among non-anaplastic tumor cells.
- Diffuse anaplasia refers to anaplastic cells arranged in multiple clusters or diffuse sheets.
- The presence of anaplasia confers a worse prognosis (see Clinical), especially when the anaplasia is diffuse
- No distinct translocation
- Common sites of involvement:
- Extremities
- Trunk
- Retroperitoneum
- Rare, <1% of rhabdomyosarcoma
- Reported in children and adults of all ages
- Unknown behavior
