Inventrust Properties (IVT) had the highest return between 2013 and 2015 by a mid-cap US stock, returning 786.5%.

ASSET	YEARS	% RETURN
Inventrust Properties (IVT)	2013-2015	786.49%
Vipshop (VIPS)	2013-2015	748.78%
CleanSpark (CLSK)	2013-2015	682.62%
ACADIA Pharmaceuticals (ACAD)	2013-2015	645.82%
Celsius (CELH)	2013-2015	593.14%
Pampa Energia SA ADR (PAM)	2013-2015	490.52%
Ionis Pharmaceuticals (IONS)	2013-2015	482.6%
Catalyst Pharmaceuticals (CPRX)	2013-2015	463.22%
Nexstar Broadcasting (NXST)	2013-2015	463.13%
Ligand Pharmaceuticals (LGND)	2013-2015	409.49%
TAL Education (TAL)	2013-2015	379.08%
Skechers (SKX)	2013-2015	375.25%
Ambarella (AMBA)	2013-2015	365.28%
Globalstar, Inc Common Stock (GSAT)	2013-2015	350%
Repligen (RGEN)	2013-2015	342.03%
YY Inc Class A (YY)	2013-2015	330.83%
EPAM Systems (EPAM)	2013-2015	324.51%
Alkermes (ALKS)	2013-2015	317.79%
Transportadora de Gas del Sur SA ADR (TGS)	2013-2015	289.32%
Alaska Air (ALK)	2013-2015	276.03%
Skyworks Solutions (SWKS)	2013-2015	271.09%
BBVA Banco Frances SA ADR (BBAR)	2013-2015	265.43%
Dycom Industries (DY)	2013-2015	248.23%
Amicus Therapeutics (FOLD)	2013-2015	243.97%
BGC (BGC)	2013-2015	241.74%

Mid-cap stocks are treated as having a market cap between $2B and $10B.