17-year-old girl, with a rapidly growing bulge in the soft tissue of the groin and lower abdominal wall. Biopsy.
- Cell-dense tumour tissue degenerative “caves“ (alveolar pattern)
- Cells with moderate to high pleomorphism depending on the degree of differentiation: there are small round without much cytoplasm and larger cells with an excentric nucleus and eosinophilic, fibrillar cytoplasm, as well as some multinucleated giant cells. Glycogen positive. Mitoses can be seen.
Rhabdomyosarcomas do not originate from skeletal muscle but from undifferentiated mesenchymal cells. The tumour cells show varying occurrence of skeletal muscle cell features such as striation or expression of typical muscle proteins (desmin, myoglobin) and transcription factors (myogenin). The alveolar variant is named after its building pattern, namely the cavities that occur due to degenerating tumour mass.
Often only some larger cells show ultrastructured bundles of myofilaments, which occasionally are arranged so that light microscopy shows apparent striation. Other common variants, especially in children, are embryonal rhabdomyosarcomas which appear as “round cell sarcomas” (refer to specimen S
The neoplastic cells are undifferentiated, striation is not evident.
Immunohistochemical markers: desmin, myogenin.