Billionaire Stan Druckenmiller’s 5 Small and Mid-Cap Stock Picks with Huge Upside Potential

2. Insmed Incorporated (NASDAQ:INSM)

Duquesne Capital’s Stake: $258 Million

Insmed Incorporated (NASDAQ:INSM) first appeared in the 13F portfolio of Duquesne Capital back in the second quarter of 2020. This position comprised 1.2 million shares and was sold off by the next quarter. A new position was opened in the stock in the second quarter of 2024. This holding consisted of just 20,000 shares. However, the fund upped this to over 2.4 million shares by the third quarter of 2025. Filings for the fourth quarter of 2025 reveal that the fund owned nearly 1.5 million shares in the firm, down 38% compared to the previous quarter.

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Hedge fund interest in Insmed Incorporated (NASDAQ:INSM) stock is primarily due to the successful transitioning of the firm from a clinical-stage biotech into a commercial powerhouse with a dominant lead in rare lung diseases. The commercial performance of Brinsupri, the first-ever approved treatment for non-cystic fibrosis bronchiectasis, is the most important. In its first full quarter of launch (Q4 2025), Brinsupri generated $144.6 million, shattering analyst expectations. CEO Will Lewis noted that Insmed essentially owns this entire disease category with no immediate competition. Hedge funds are pricing in peak sales of $5 billion+, with 2026 guidance already set at a minimum of $1 billion.