Is Tango Therapeutics Stock a Buy, Sell, or Hold After Major Shareholder Third Rock Ventures Sold Nearly Half a Million Shares?

Venture capital fund Third Rock Ventures IV, L.P., a 10% owner of Tango Therapeutics, Inc. (NASDAQ:TNGX), reported the sale of 477,401 shares in an open-market transaction on October 23, 2025, according to an SEC Form 4 filing.

Transaction summary

Transaction value is based on the SEC Form 4 weighted average purchase price ($10.15), while post-transaction value is calculated using the market close price on October 23, 2025.

Key questions

How significant was the sale relative to Third Rock Ventures IV, L.P.'s direct holdings?
The 477,401 shares sold represented 3.44% of direct ownership as of October 23, 2025, reducing the insider's stake to 13,386,574 shares, or 12.03% of outstanding shares on that date.

How does this transaction compare to Third Rock Ventures IV, L.P.'s historical trade sizes?
The sale exceeded the historical median for sell-only transactions (292,799 shares) and matched the recent period's median (363,541 shares), but was below the largest sale (1,100,000 shares on August 19, 2025).

What was the market context at the time of the transaction?
Shares were priced at approximately $10.15 for this transaction.

Did this transaction materially change Third Rock Ventures IV, L.P.'s ownership position?
While the sale reduced direct holdings, the insider remains a major shareholder with a post-transaction value of approximately $100.8 million at the market close on October 23, 2025.

Company overview

* 1-year price change calculated using October 23, 2025 as the reference date.

Company snapshot

Tango Therapeutics, Inc. is a clinical-stage biotechnology company specializing in the discovery and development of novel cancer therapies using synthetic lethality. The company has a pipeline targeting genetically-defined tumors.

IMAGE SOURCE: GETTY IMAGES.

Tango Therapeutics has a strategic collaboration with Gilead Sciences, Inc. for the discovery, development, and commercialization of therapies for patients with cancer.

The company develops targeted oncology therapeutics, including lead candidates TNG908 for MTAP-deleted cancers and a USP1 inhibitor for BRCA1/2-mutant cancers.

It operates a research-driven model and maintains strategic collaborations, notably with Gilead Sciences. Tango Therapeutics serves pharmaceutical partners with a focus on patients with genetically defined cancers.

Foolish take

Third Rock Ventures' sale of almost half a million shares of Tango Therapeutics looks like profit taking. After the transaction, Third Rock Ventures still holds over 13 million shares in the biotech company.

The venture capital fund shedding some shares makes sense. Tango Therapeutics hit a 52-week high on Oct. 16, and the stock is up nearly 160% in 2025 through Oct. 30.

Third Rock Ventures sold shares on the day Tango Therapeutics reported that data for its experimental cancer drug, vopimetostat, revealed encouraging results from clinical trials. On the same day, the biotech company also announced it had raised $225 million in funding.

The funding is good news for investors, especially since Tango Therapeutics is not profitable and revenue is down in 2025 compared to 2024. In the second quarter, sales were $3.2 million compared to $19.9 million last year, primarily from a licensing deal with Gilead Sciences. The company also had a Q2 operating loss of $41 million.

Given Third Rock Ventures maintains a significant investment in Tango Therapeutics, its sale of some of its stock isn't an urgent sign to sell yours if you're a shareholder. You can decide to hold or to follow Third Rock Ventures' lead to take some profit.

But if you're weighing whether to invest, now isn't the time. Tango Therapeutics shares are quite expensive with a price-to-sales ratio of 35. Wait for the stock to drop before deciding to buy.

Glossary

Insider: An individual or entity with access to non-public company information, often including major shareholders or executives.
Open-market transaction: The buying or selling of securities on a public exchange, rather than through private arrangements.
Form 4: A required SEC filing that reports changes in ownership of a company's securities by insiders.
10% owner: An individual or entity holding at least 10% of a company's outstanding shares, subject to specific SEC reporting rules.
Direct ownership: Shares held and controlled directly by an individual or entity, not through intermediaries.
Outstanding shares: The total number of a company's shares currently held by all shareholders, including insiders and the public.
Weighted average purchase price: The average price paid per share, weighted by the number of shares in each transaction.
Median: The middle value in a set of numbers, with half above and half below.
Clinical-stage: Refers to a biotechnology or pharmaceutical company with drug candidates being tested in human clinical trials.
Synthetic lethality: A therapeutic approach targeting two genes or pathways, where simultaneous disruption leads to cell death, often used in cancer treatment.
Strategic collaboration: A formal partnership between companies to jointly develop, research, or commercialize products or technologies.
TTM: The 12-month period ending with the most recent quarterly report.

Robert Izquierdo has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.