enGene’s detalimogene (nonviral gene therapy candidate) reported updated data in its Phase II LEGEND trial in high-risk, BCG-unresponsive nonmuscle invasive bladder cancer with carcinoma in situ (CIS±papillary), driving a sharp stock selloff. Updated results showed complete response rates declined versus a prior November 2025 readout. As of an April 21 data cutoff, 67 of 124 evaluable patients achieved a 54% complete response at any time, compared with 43% at six months (52 of 121). enGene previously reported 63% complete response at any time and 62% at six months for the first 62 patients. At nine months, the company cited a 32.7% complete response rate, falling to 13.3% at 12 months. enGene said durability outcomes remain incomplete and it plans to continue discussions with the FDA on statistical analysis plans and potential BLA filing. The market reaction underscores how updated efficacy and durability metrics—especially in competitive NMIBC categories—can quickly reshape expectations even when companies emphasize data immaturity.