Pleomorphic Rhabdomyosarcoma
Definition
- Malignant neoplasm with large pleomorphic cells exhibiting skeletal muscle differentiation
Diagnostic Criteria
- Unfavorable histologic type
- 5-year failure free survival rate: ~ 40%
- Markedly enlarged pleomorphic cells
- Abundant deeply eosinophilic cytoplasm
- Multinucleated forms may be seen
- Spindled to epithelioid neoplastic cells admixed
- Lacks background of uniform immature cells
- Presence of immature cells suggests instead anaplasia in embryonal or alveolar subtypes
- Requires demonstration of skeletal muscle differentiation
- 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
- Anaplasia can be very difficult to assess in pleomorphic subtype
- No distinct translocation
- Common sites of involvement:
- Deep extremities
- Retroperitoneum
- Most often seen in adults
- Rare cases reported in children
