Why Is Sanofi Stock Falling Thursday?

Core Viewpoint - Sanofi SA's stock declined after the late-stage trial results for amlitelimab, a potential successor to Dupixent, did not meet investor expectations, raising concerns about the company's dermatology franchise sustainability post-patent expiration [1] Group 1: Trial Results - The global COAST 1 phase 3 study indicated that amlitelimab met all primary and key secondary endpoints, showing statistically significant skin clearance and disease severity improvement compared to placebo at Week 24 for patients aged 12 years and older with moderate-to-severe atopic dermatitis [2] - However, the efficacy of amlitelimab and Amgen's rocatinlimab in Phase 3 studies did not reach the benchmark set by Dupixent, which demonstrated a 36% improvement on EASI-75 over placebo [3] Group 2: Comparison with Competitors - Analyst observations noted that both rocatinlimab and amlitelimab offer a more favorable dosing schedule compared to Dupixent, with potential for monthly or quarterly dosing, respectively [4] - The results suggest that OX40/OX40L therapies, including amlitelimab, may provide slower and less robust responses than IL-13/4 drugs, likely confining their use to second-line treatments for patients who do not respond to IL-13/4 options [4] Group 3: Market Dynamics - Advanced therapies account for less than 20% of the atopic dermatitis market, with only three approved mechanisms (IL-13/4, IL-31, JAK), indicating a potential market opportunity for OX40 drugs, albeit smaller than for therapies that match or exceed IL-13/4 efficacy [5] - Ongoing discussions focus on the differences between amlitelimab and rocatinlimab, particularly regarding side effects like pyrexia and chills [5] Group 4: Side Effects and Dosing - Amgen's rocatinlimab is associated with immune-related side effects, including pyrexia (10%) and chills (6%), which may have limited dosing in Phase 3 trials to 300 mg, below the 600 mg tested in Phase 2, potentially affecting its efficacy [6] - In contrast, amlitelimab exhibited lower rates of pyrexia (1.1% vs. 0.7% placebo) and chills (0.4% vs. 0.0% placebo), while achieving comparable efficacy to rocatinlimab at higher dose levels [6] Group 5: Stock Performance - Following the trial results, Sanofi's stock price fell by 8.59% to $45.61 [7]