Alnylam, Sarepta, and Day One: The JPM Preannouncement Showdown and What Was Priced In

The first day of the J.P. Morgan Healthcare Conference set the tone for a classic expectation game. Three companies-Alnylam, Day One, and Sarepta-delivered their preannouncements, and the market's verdict was clear: reactions diverged sharply based on whether reality met or missed the whisper numbers.

Alnylam Pharmaceuticals kicked off the session with a sales report that showed growth but fell short of the Street's modest target. The company preannounced Q4 Amvuttra sales of $827 million, a figure that "modestly" missed the Street's call for $852 million to $861 million. The immediate stock reaction was a sell-off, a textbook "sell the news" move where the print, while solid, was simply not enough to justify further gains. The expectation gap here was narrow but real.

In stark contrast, Day One Biopharmaceuticals delivered a powerful beat and raise. The company announced preliminary unaudited 2025 OJEMDA net product revenue of $155.4 million, representing a staggering 172% year-over-year increase. More importantly, it provided forward guidance that doubled down on the growth story, projecting 2026 OJEMDA U.S. net product revenue of $225–$250 million. This combination of explosive past growth and confident future outlook drove a positive market reaction, as the company clearly exceeded expectations on both fronts.

Sarepta Therapeutics took a different approach, choosing to present without a financial preannouncement. The company was scheduled to present at the conference, but no new financial preannouncements were made. Its stock held steady, reflecting a market that had already priced in its existing trajectory and was waiting for substantive updates. The lack of new data meant no catalyst to move the needle one way or the other.

The initial verdict was a direct reflection of these differing outcomes. Alnylam sold off on a modest miss, Day One rallied on a powerful beat and raise, and Sarepta held steady with no new information. This trio of reactions perfectly illustrates the core dynamic of the preannouncement show: the market's move is less about the absolute numbers and more about the gap between what was priced in and what was actually delivered.

Expectations vs. Reality: Why Each Company Reacted Differently

The divergent market reactions on Day One of JPMorgan were a direct function of how each company's preannouncement data compared to the expectations already baked into its stock price. For Alnylam, the market had priced in a strong beat for the quarter. The company's preannounced Q4 Amvuttra sales of $827 million fell short of the Street's call, creating a classic "sell the news" dynamic. Even against a backdrop of a broader commercial breakout, the modest miss meant reality did not meet the whisper number, prompting a sell-off.

Day One's reaction was the opposite, driven by a massive beat on growth. The company announced preliminary unaudited 2025 OJEMDA net product revenue of $155.4 million, a 172% year-over-year increase. This explosive growth rate was likely not fully priced in, and the subsequent guidance that doubled down on the story provided a clear path forward. The combination of a powerful past print and confident future outlook exceeded expectations on both fronts, leading to a rally.

Sarepta's steady stock reflected neutral expectations. The company was scheduled to present at the conference, but no new financial preannouncements were made. With no new data to surprise the market, the stock held its ground. The verdict was a market that had already priced in its existing trajectory and was waiting for substantive updates, finding none in the preannouncement phase.

What Was Priced In: The Whisper Numbers and Guidance Resets

The preannouncement show is over, but the real game begins now. The forward-looking guidance and long-term targets each company presented will set the new baseline for what the market is pricing in for their future. These are the new whisper numbers.

For Alnylam, the robust 2026 product sales guidance of $4.9–$5.3 billion is the key reset mechanism. This represents a significant beat on the prior year and provides a clear, high-visibility target. After the Q4 miss, this guidance is crucial for rebuilding momentum. It signals that management still expects a powerful commercial breakout, likely pricing in continued Amvuttra growth and the ramp of its pipeline assets. The market will now focus on whether execution hits this new, higher bar.

Day One's guidance implies even steeper expectations. Its projection for 2026 OJEMDA U.S. net product revenue of $225–$250 million implies roughly 45% growth from its 2025 run-rate. This is not just a beat; it's a signal that the market is pricing in the drug's rapid adoption in its niche. The guidance sets a high watermark for 2026, making any stumble in that growth trajectory a potential catalyst for disappointment.

Sarepta's setup is different. With no financial preannouncement made, the market is likely pricing in steady execution on its existing pipeline and the potential for future gene therapy approvals. The company's scheduled presentation is the next catalyst, but for now, expectations are neutral. The market is waiting for substantive updates on its Duchenne programs or new data to reset the forward view. Without a guidance reset, the stock's path will be driven by clinical and regulatory milestones, not financial targets.

The bottom line is that guidance resets expectations. Alnylam is trying to move past a minor miss with a powerful forward target. Day One has set a high bar for its explosive growth story. And Sarepta is holding the line, with the market waiting for the next piece of news to shift the narrative.

Catalysts and Risks: What to Watch for Each Thesis

The preannouncement show is over, but the real test for each stock begins now. The market has reset its expectations based on the guidance and targets presented. The next moves will depend on whether these companies can hit the new, higher bars set for them.

For Alnylam, the near-term catalyst is the planned 2028 launch of nucresiran for polyneuropathy. This is the next major commercial milestone that will extend its TTR leadership. The key risk, however, is pressure from generic competition. The company's robust 2026 sales guidance of $4.9–$5.3 billion creates a high watermark. Any sign of Amvuttra sales growth slowing before the nucresiran launch could signal that the commercial breakout is not as durable as priced in.

Day One's immediate catalyst is the completion of Phase 3 FIREFLY-2 enrollment in H1 2026, with the data readout expected in mid-2027. This trial is critical for securing the drug's label expansion and reinforcing its growth trajectory. The company's aggressive 2026 revenue guidance of $225–$250 million implies roughly 45% growth from its 2025 run-rate. Execution must be flawless to hit that target, making the FIREFLY-2 timeline a key watchpoint for any deviation from the growth plan.

Sarepta's thesis hinges on execution. The company is scheduled to present at the conference, but no new financial preannouncements were made. The primary risk is that its gene therapy pipeline, while promising, faces the usual hurdles of clinical development and regulatory approval. The catalysts are clear: potential regulatory milestones for its Duchenne muscular dystrophy programs. The market is waiting for substantive updates to shift the narrative from steady execution to a new growth inflection. Without a guidance reset or major clinical news, the stock may remain in a holding pattern.