Cytokinetics (CYTK) had the highest return in December 2014 by a large-cap US stock, returning 72.3%.

ASSET	MONTH	% RETURN
Cytokinetics (CYTK)	December 2014	72.26%
QXO (QXO)	December 2014	29.41%
Arrowhead Pharmaceuticals (ARWR)	December 2014	28.13%
MACOM Technology Solutions (MTSI)	December 2014	25.88%
Axon Enterprise (AXON)	December 2014	24.03%
Coeur Mining (CDE)	December 2014	21.67%
Ionis Pharmaceuticals (IONS)	December 2014	19.65%
Comfort Systems USA (FIX)	December 2014	18.72%
Restaurant Brands International (QSR)	December 2014	18.37%
Ciena (CIEN)	December 2014	17.57%
Advanced Energy Industries (AEIS)	December 2014	16.69%
Genmab A-S (GMAB)	December 2014	16.55%
Stonex (SNEX)	December 2014	16.35%
Hecla Mining (HL)	December 2014	16.25%
Lululemon Athletica (LULU)	December 2014	15.77%
Hudbay Minerals (HBM)	December 2014	15.58%
SS&C Technologies (SSNC)	December 2014	15.5%
Powell Industries (POWL)	December 2014	15.19%
Heico (HEI)	December 2014	14.22%
Dycom Industries (DY)	December 2014	14.15%
Onto Innovation (ONTO)	December 2014	13.34%
Ryanair Holdings PLC ADR (RYAAY)	December 2014	12.7%
TTM Technologies (TTMI)	December 2014	12.56%
Neurocrine Biosciences (NBIX)	December 2014	12.26%
Royal Caribbean Cruises (RCL)	December 2014	12.13%

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