Prothena stock holds near USD 9.60 after market cap update

Prothena Corporation plc (IE00B91XRN20) traded at USD 9.60 on September 4, 2026, with a market capitalization of about USD 492.8 million. The latest visible snapshot also showed the stock down 0.88 percent.

Market value stays compact

That price sits close to the same-day level of USD 9.63 shown in another market snapshot, which implies only a small intraday gap of USD 0.03. For investors, that keeps the focus on valuation and cash discipline rather than a large price swing.

Yahoo Finance also showed Prothena at USD 9.74 with a market cap of USD 500.0 million on September 4, 2026, which places the shares in a narrow band around the USD 9.60 mark. The range across those snapshots points to a stock that is trading with limited distance between the listed quotes.

Biotech at a small scale

Prothena remains a biotechnology company, and the current market data underline that the equity is still priced as a sub-USD 1 billion name. The available snapshots put the company between USD 492.8 million and USD 500.0 million in market value on September 4, 2026.

That scale matters because the stock can react sharply to any new clinical or financing detail, even when the headline price move itself is modest. The market cap and share price together show how compact the equity story still is.

Key data

Company data

Prothena stock remains a biotechnology name with a market capitalization just below USD 500 million on September 4, 2026. The most visible numbers in the current snapshot are USD 9.60, USD 9.63 and USD 9.74, which frame the stock in a tight range.