The litigation targets the period between August 1, 2025, and May 15, 2026, centering on how the company communicated delays in progression-free survival (PFS) event accrual. According to the filing in the Southern District of New York, Regeneron repeatedly framed these delays as potentially indicative of positive treatment performance. Investors claim these statements masked underlying statistical vulnerabilities that were only revealed through subsequent protocol amendments and the final trial failure.

The financial impact on shareholders became evident in late April and May 2026. On April 29, 2026, following a disclosure regarding changes to the PFS analysis, the stock price fell by $45.41. The trend intensified after May 15, 2026, when the company confirmed the trial did not achieve statistical significance. Between April 28 and May 18, 2026, Regeneron shares dropped from $731.77 to $629.68, marking a 13.95% decline. Investors seeking lead plaintiff status must file their applications by September 14, 2026.