Longleaf Partners Fund Q3 2026 Portfolio Review

Avantor is regaining confidence in its organic growth prospects and CEO Emmanuel Ligner’s turnaround plan. Regeneron reported solid results, with Dupixent growth exceeding the author’s and market expectations. Fortune Brands Innovations shares fell in Q3, reversing the prior quarter’s gain tied to excitement over Jesse Singh’s appointment as CEO.

Analysis

The read-through to Avantor is supportive but indirect: strong biologic demand can reinforce long-run demand for research and production inputs, yet the article provides no evidence that Regeneron’s results translate into Avantor orders or near-term revenue. Treat Avantor’s turnaround as an execution thesis, not a proxy for one drug’s momentum. Verify organic growth, order trends, and management guidance before upgrading conviction.

For Regeneron, continued Dupixent strength is a positive product-level signal, but investors should distinguish franchise growth from the economics recognized by Regeneron; the product is developed and commercialized with Sanofi. In the next few days, sentiment may dominate. Over the next 1–3 months, reported product sales and forward guidance matter more. The thesis weakens if growth decelerates or results fail to convert into improved outlook.

Fortune Brands’ retracement suggests CEO-related enthusiasm was not durable, but price action alone is not evidence the turnaround has failed. Over 6–18 months, execution must show up in demand, margins, or guidance; housing and remodeling conditions could also overwhelm company-specific progress. With no valuation, forecast revisions, or operating metrics supplied, there is not enough here to justify a directional trade or infer that the move is mispriced.

Key Decisions for Investors

• AVTR: Keep on the watchlist rather than buying the Regeneron read-through. Reassess after the next report for sustained organic growth and order improvement; a guide-down or renewed contraction would falsify the turnaround case.
• REGN: Maintain exposure only if supported by the full earnings outlook, not Dupixent momentum alone. Check Regeneron’s reported economics and guidance alongside Sanofi’s franchise disclosures before attributing growth to REGN.
• FBIN: Do not treat the Q3 pullback as a standalone short signal. Wait for operating evidence; deteriorating guidance or margins would strengthen the bearish case, while stabilization alongside execution would argue against it.
• No immediate pair trade: the article supplies no relative valuation, estimate-revision, or operating data to establish that AVTR is better positioned than FBIN. Track earnings revisions and sector demand indicators for a clearer entry.