HER2 antibody-drug conjugates are active against desmoplastic small round cell tumor.

ERBB2/HER2 was detectable in DSRCT samples from patients and PDXs, with higher sensitivity of RNA assays and improved IHC detectability using Clone 29D8. Treatment of ERBB2/HER2-expressing DSRCT PDX, cell line, and organoid models with T-DXd or T-DM1 resulted in tumor regression. This therapeutic response was long-lasting in T-DXd-treated xenografts and was mediated by rapid HER2-ADC complex internalization and cytotoxicity, triggering p53-mediated apoptosis and growth arrest. Xenograft regression was associated with bystander payload effects triggering global tumor niche responses proportional to HER2 status. Conclusions ERBB2/HER2 is a therapeutic target for DSRCT. HER2-ADCs are novel options for managing this exceptionally aggressive sarcoma and may fulfill its urgent and historically unmet need for more effective clinical therapy.