In a note out early Tuesday, RBC Capital Markets analyst Brian Abrahams lays out the potential second-order effects of the aducanumab decision. He says not only to be ready for a dramatic move in Biogen stock (ticker: BIIB), but in the shares of other companies with Alzheimer’s programs, those with controversial drugs seeking FDA approval, and even companies that might be acquisition targets for Biogen.

Companies that Abrahams says could see their share price shift on an aducanumab decision include Denali Therapeutics (DNLI), Sarepta Therapeutics (SRPT), Ionis Pharmaceuticals (IONS), Eli Lilly (LLY), and Intercept Pharmaceuticals (ICPT).

What’s more, Abrahams say that Biogen and its aducanumab partner, the Japanese pharmaceutical firm Eisai (ESALY), are large enough that a dramatic move in their share prices will on its own move stock indexes.

“FDA’s upcoming decision on aducanumab is not only binary for BIIB but also likely to reverberate throughout the biopharma sector, influencing overall sentiment on the space, perceptions on regulatory flexibility, and business development dynamics,” Abrahams wrote. “With sector sentiment negative, the adu decision has potential to rapidly turn perceptions around or, conversely, to double down on recent apathy.”

Biogen shares are up 9.2% so far this year, and down 11.3% over the next 12 months. The stock was up 1.8% in recent premarket trading. The FDA’s deadline for an aducanumab decision is June 7, though an announcement could theoretically come anytime before that. The agency’s decision has been delayed before—the original deadline was March 7, before the FDA announced a delay in late January.

The decision comes amid a slump in biotech shares. The SPDR S&P Biotech ETF (XBI) is down 9.2% so far this year. The aducanumab decision could scramble the sector in complex ways.

In his note, Abrahams noted that no new Alzheimer’s therapy has been approved in two decades, and that approval would blaze a path for future approvals. “If approved, [aducanumab] would set multiple precedents, including on development endpoints used, quality and extent of evidence packages submitted, and a bar for benefit/risk—essentially creating a framework for future AD development,” he wrote.

That would be good for Denali, Lilly, and others working on their own Alzheimer’s therapies, he said. On the other hand, approval might make it harder for those companies to sign up patients for Alzheimer’s drug trials.

If the FDA rejects the drug, Abrahams wrote, that would make Biogen desperate to strike deals for new products. Virtually all of Biogen’s key products are facing competitive threats. Abrahams wrote that an FDA rejection could lead to a rise in shares of companies seen as acquisition targets for Biogen, including Sarepta, or even its current partners Sage and Ionis.

Another wild card, Abrahams writes, is that the decision could be taken by investors as an indication of the FDA’s mood. “We believe a common convergent view for some time has been that the FDA’s ruling on adu …would set the regulatory tone for years to come, particularly with a new administration,” Abrahams writes.

While Abrahams sees problems with that thesis, he says that because investors seem to believe it, it will have an impact on shares of companies like Sarepta, Intercept, and others.

Early Tuesday, shares of Sarepta were down 1.7%, while shares of Intercept were up 2.3%. Biogen is off 0.3%.

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