$ATRA is one of biggest losers #stocks today. read more:

Atara Biotherapeutics, Inc. (symbol: ATRA) was one of the worst losers of
the trading day today (2015-10-21), losing -10.91%. The number of shares
that changed hands was 545,838, or about 2 times the average daily volume
in the stock.
The closing price was $24.99, amounting to a market cap of $712,510,000,
about -61.88% off the highest price in the last 12 months. The stock has
been trading at a range between $12.61 and $65.56.
ATRA is in the Biotechnology: Biological Products (No Diagnostic
Substances) industry, part of the Health Care sector. It first went public
in 2014.