Parabilis Medicines Inc. shares rocketed 67% in their first day of trading, pricing an upsized IPO at $20 per share and opening at $33.35. The Cambridge-based clinical-stage oncology company raised nearly $745 million after increasing the deal size Tuesday, giving it a roughly $4 billion market valuation.

Regeneron Pharmaceuticals Inc. simultaneously purchased 4.17 million shares for $75 million at $18 apiece, building on a May research collaboration that included a $50 million upfront payment. The offering attracted demand roughly ten times the original share count before Tuesday's expansion.

Founded in 2015, Parabilis develops therapies targeting various cancers and rare tumors. The company plans to advance its lead candidate zolucatetide through later-stage trials. CEO Mathai Mammen, formerly of Johnson & Johnson, aims to create a new category of peptide-based medicines to target proteins considered undruggable.

Parabilis reported a net loss of $145.9 million for 2025 with $27.7 million in cash, compared to $117.9 million in losses and $47.3 million in cash the prior year. Shares trade on Nasdaq under PBLS. The strong debut signals investor appetite for innovative cancer therapeutics despite the company's preclinical stage.