EXACT Sciences (EXAS) had the worst month in 2015 by a large-cap US stock in October 2015, returning -54.9%.

ASSET	MONTH	% RETURN
EXACT Sciences (EXAS)	October 2015	-54.92%
Alamos Gold (AGI)	July 2015	-42.48%
Kinder Morgan (KMI)	December 2015	-36.78%
Leonardo DRS, Inc Common Stock (DRS)	July 2015	-36.6%
Insulet (PODD)	January 2015	-36.22%
Freeport-McMoran Copper & Gold (FCX)	July 2015	-36.15%
United States Steel (X)	September 2015	-34.18%
Leonardo DRS, Inc Common Stock (DRS)	November 2015	-33.34%
Micron Technology (MU)	June 2015	-32.62%
ArcelorMittal SA ADR (MT)	September 2015	-31.97%
Targa Resources (TRGP)	December 2015	-31.39%
United States Steel (X)	November 2015	-30.7%
AngloGold Ashanti (AU)	July 2015	-30.69%
XPO Logistics (XPO)	September 2015	-30.69%
Freeport-McMoran Copper & Gold (FCX)	November 2015	-30.62%
Natera (NTRA)	September 2015	-30.4%
Targa Resources (TRGP)	November 2015	-30.29%
Devon Energy (DVN)	December 2015	-30.13%
Allegheny Technologies (ATI)	July 2015	-29.8%
Pure Storage (PSTG)	November 2015	-29.65%
Banco Bradesco SA ADR (BBD)	March 2015	-29.38%
Teck Resources Ltd Class B (TECK)	September 2015	-28.47%
Williams Companies (WMB)	December 2015	-28.27%
Dr Reddy’s Laboratories Ltd ADR (RDY)	November 2015	-28.16%
Deckers Outdoor (DECK)	January 2015	-27.99%

Large-cap stocks are treated as having a market cap of $10B+.