Definium CEO sold 31,550 shares under plan

Posted by Brenda Bartman on Oct 2nd, 2026

What happened

Robert Barrow, chief executive officer and a director of Definium Therapeutics, Inc. (NASDAQ: DFTX), sold 31,550 shares on 2026-09-25. The filing puts the weighted average price at $36.57 and the sale value at about $1.15 million. It says he held 2,213,090 shares and that the trade was made under a Rule 10b5-1 plan. A footnote says the sale satisfied withholding tax obligations tied to settled vested restricted stock units, and that the shares traded in transactions at $36.24 to $36.98.

Key numbers

Metric	Latest	Source
Shares sold	31,550 shares	SEC Form 4
Weighted average sale price	$36.57 per share	SEC Form 4
Total value of sale	about $1.15 million	SEC Form 4
Shares held after sale	2,213,090 shares	SEC Form 4
Sale price range	$36.24 to $36.98 per share	SEC Form 4
Sold shares as share of pre-trade holdings	about 1.4%	Calculated from SEC Form 4

Why it matters

OptimistFi's case is that Definium is a financed clinical-stage therapeutics option, so clinical or regulatory de-risking matters most. This filing is mixed for that view because it changes insider ownership, not the pipeline. The 31,550 shares were about 1.4% of Barrow's pre-trade holding of 2,244,640 shares. That makes the sale small relative to the remaining stake, while the filing still leaves him with 2,213,090 shares after the trade.

The same filing says the shares were sold to satisfy withholding tax obligations tied to vested restricted stock units. It also says the trade followed a Rule 10b5-1 plan adopted on June 15, 2022, which points to a preset program rather than a fresh one-off decision. The reported price was a weighted average sales price, and the individual transactions ran from $36.24 to $36.98 on 2026-09-25. That framing is the main caveat for investors.

Browse: stock research on every company OptimistFi covers

What's next

Later Form 4 reports will show whether Barrow's 2,213,090-share stake changes again. A stable stake would keep this filing as a routine ownership update.

More sales under the same plan would extend the same pattern. If no further sales appear, the current ownership baseline stays intact for the next insider report. That leaves the post-sale stake as the baseline for the next insider filing. The position size matters more than the one-time sale price for judging ownership drift.

Sources

SEC Form 4 — Robert Barrow sold 31,550 shares on 2026-09-25 and held 2,213,090 afterward.
Calculated from SEC Form 4 — 31,550 shares were about 1.4% of the holding before the trade.

Read the full OptimistFi thesis on Definium Therapeutics, Inc.: https://optimistfi.com/stocks/DFTX

See what would break the Definium Therapeutics, Inc. thesis and track it live on the OptimistFi Thesis-Break Engine.

Browse every company OptimistFi covers at optimistfi.com/stocks, or read the latest evidence-first research.

The full Definium Therapeutics, Inc. investment case, its status and the next test to watch live on the Definium Therapeutics, Inc. thesis page.

Originally published on OptimistFi, evidence-first equity research. More at optimistfi.com.