Sanofi terminated development of Nurix’s Phase 1 immunology candidate SAR448272 (NX-3911), ending part of a collaboration spanning protein degradation drug discovery. The write-down hit sentiment hard: Nurix shares dropped about 38% after the announcement, even though the companies said the remainder of the collaboration continues. The setback underscores how portfolio-level dependency on early-stage pipeline progress—and milestone timing—can rapidly alter biotech valuations, particularly when programs are tied to large multi-year discovery deals with material milestone economics.