Regeneron's Sharp Intraday Drop: What's Fueling the Selloff Amid Gene Therapy Hype?

Summary
• Regeneron (REGN) plunges 3.01% to $756.67, its lowest since October 2025
• Gene therapy collaboration with Tessera Therapeutics sparks regulatory scrutiny
• FDA approval of Eylea HD in August failed to sustain momentum

Regeneron’s stock faces a dramatic intraday selloff amid mixed signals from its gene therapy partnerships and recent product approvals. With the biotech sector under pressure and technical indicators flashing caution, investors are scrambling to decipher whether this drop marks a buying opportunity or a deeper correction.

Gene Therapy Hype Meets Regulatory Realism
Regeneron’s 3.01% decline stems from renewed scrutiny over its gene therapy collaboration with Tessera Therapeutics, announced just 6 hours prior. While the partnership aims to develop AATD therapies, analysts question the regulatory pathway for in vivo gene editing. Additionally, recent FDA approvals like Eylea HD in August have failed to translate into sustained momentum, with the stock now trading below its 52-week high of $800.99. Short-term traders are reacting to the broader biotech sector’s volatility, as Amgen (AMGN) also dips 1.98%, signaling sector-wide caution.

Biotech Sector Mixed as Amgen Trails Regeneron’s Slide
The biotech sector remains fragmented, with Amgen (AMGN) down 1.98% and Novo Nordisk (NVO) underperforming the S&P 500. Regeneron’s selloff contrasts with recent gains in gene therapy peers like CRISPR Therapeutics, though its 21.5% monthly surge since August suggests overbought conditions. The sector’s reliance on regulatory outcomes—particularly for gene editing—heightens near-term uncertainty.

Options Playbook: Capitalizing on Volatility and Key Levels
• MACD: 44.15 (above signal line 36.77), RSI: 82.17 (overbought), Bollinger Bands: $595.99–$804.91
• 200D MA: $597.75 (far below current price), Support/Resistance: 556.09–562.18 (200D), 575.69–579.92 (30D)

Regeneron’s technicals suggest a short-term overbought condition, with RSI at 82.17 and MACD above its signal line. The stock is trading near the upper Bollinger Band ($804.91), indicating potential for a pullback. Key support levels at $755 (lower Bollinger Band) and $745 (critical psychological level) will be critical for bulls. The 200-day MA at $597.75 remains a long-term floor.

Top Options Contracts:
• REGN20251205C750 (Call, $750 strike, 2025-12-05):
- IV: 33.17% (moderate)
- Leverage Ratio: 49.43% (high)
- Delta: 0.5978 (moderate sensitivity)
- Theta: -4.23 (rapid time decay)
- Gamma: 0.013177 (moderate price sensitivity)
- Turnover: 23,932 (liquid)
- Price Change Ratio: -57.50% (aggressive)
- Why: High leverage and moderate delta make this ideal for a short-term rebound trade if the stock breaks above $755.

• REGN20251205C755 (Call, $755 strike, 2025-12-05):
- IV: 28.52% (moderate)
- Leverage Ratio: 69.26% (very high)
- Delta: 0.5331 (moderate sensitivity)
- Theta: -3.78 (rapid time decay)
- Gamma: 0.015748 (moderate price sensitivity)
- Turnover: 13,092 (liquid)
- Price Change Ratio: -68.70% (aggressive)
- Why: High leverage and liquidity position this as a speculative play if the stock stabilizes near $755 support.

Payoff Estimation:
For a 5% downside to $718.84, REGN20251205C750 would yield $0 payoff (strike $750 > $718.84). REGN20251205C755 also yields $0. Aggressive bulls should wait for a rebound above $755 before entering.

Backtest Regeneron Stock Performance
Below is the event-driven back-test you requested. Key assumptions added automatically:1. Intraday plunge was approximated by “close-to-close return ≤ -3 %” because intraday tick data were not requested. 2. Back-test window: 3 Jan 2022 – 1 Dec 2025 (first trading day of 2022 to “now”). Summary insight (30-day holding window after each -3 % day):• 39 qualifying events found. • Day 1 (next-day close) shows a statistically significant average loss of -0.70 %. • Thereafter the average excess return versus the benchmark turns positive for up to ~15 trading days, but none of those gains are statistically significant at the 95 % confidence level. • From day 18 onward the pattern reverses to mild under-performance. • Overall, fading the immediate sell-off (buying at the next close and holding up to 15 trading days) historically offered a modest positive expectancy, but edge is weak and not persistent.Open the interactive module for full event-study curves, win-rate chart, and distribution details.Feel free to explore the module; let me know if you’d like additional slices (e.g., shorter holding periods, different plunge thresholds, or inclusion of intraday data).

Act Now: Position for a Volatile Biotech Sector Rebound
Regeneron’s selloff reflects broader biotech sector jitters, but its strong technical setup and key support levels at $755 suggest a potential rebound. With Amgen (AMGN) down 1.98%, sector-wide caution persists, but Regeneron’s gene therapy pipeline offers long-term upside. Investors should monitor the $755 level and consider the REGN20251205C750 call for a short-term bounce. If the stock breaks below $755, pivot to defensive plays in the sector.