Spindle Cell/Sclerosing Rhabdomyosarcoma (SCSRMS)
Overview
Spindle cell/sclerosing rhabdomyosarcoma is a rare subtype of rhabdomyosarcoma (RMS), classified under Soft Tissue Sarcoma in OncoTree (parent: RMS). It is characterized by a predominance of spindle cells or a sclerosing/pseudovascular pattern and is associated with MYOD1 mutations (spindle cell) or VGLL2/NCOA2 fusions (congenital/infantile sclerosing). It can be mistaken for infantile fibrosarcoma (IFS) when it arises in infancy.
Cohorts in the corpus
- sarcoma_ucla_2024: SARC0127 was initially suspected as IFS but reclassified as SCSRMS based on larotrectinib resistance in PDTOs and FISH-negative ETV6 status — the functional PDTO result was available within one week vs 18 days for definitive pathology. Part of the 24-subtype UCLA sarcoma PDTO biobank (194 specimens from 126 patients, Feb 2018–May 2022). PMID:39305899
Recurrent alterations
- ETV6: FISH-negative in SARC0127, ruling out the ETV6–NTRK3 fusion characteristic of IFS and confirming SCSRMS. PMID:39305899
- NTRK3: negative for NTRK3 rearrangement by FISH in SARC0127. PMID:39305899
Subtypes
Therapeutic landscape
- larotrectinib: resistance in SARC0127 PDTOs (expected for IFS, correctly predicted SCSRMS). The negative response was a diagnostic indicator, not a treatment failure. PMID:39305899
Sources
- PMID:39305899 — Al Shihabi et al. Cell Stem Cell 2024. UCLA sarcoma PDTO drug-sensitivity landscape.
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