Aura Minerals Inc Common Shares (AUGO) had the highest return between 2015 and 2017 by a mid-cap US stock, returning 2,802%.

ASSET	YEARS	% RETURN
Aura Minerals Inc Common Shares (AUGO)	2015-2017	2,802.01%
NexGen Energy (NXE)	2015-2017	705.03%
Caesars Entertainment (CZR)	2015-2017	681.84%
Weibo (WB)	2015-2017	624%
Pampa Energia SA ADR (PAM)	2015-2017	568.12%
Transportadora de Gas del Sur SA ADR (TGS)	2015-2017	542.61%
TAL Education (TAL)	2015-2017	536.5%
Universal Display (OLED)	2015-2017	517.9%
Corcept Therapeutics (CORT)	2015-2017	500%
Casella Waste Systems (CWST)	2015-2017	464.22%
Galapagos NV ADR (GLPG)	2015-2017	394.62%
Supernus Pharmaceuticals (SUPN)	2015-2017	376.11%
National Beverage (FIZZ)	2015-2017	350.27%
Central Garden & Pet (CENT)	2015-2017	343.78%
Installed Building Products (IBP)	2015-2017	325.25%
Grupo Financiero Galicia SA ADR (GGAL)	2015-2017	319.63%
SkyWest (SKYW)	2015-2017	306.16%
Alpha Metallurgical Resources (AMR)	2015-2017	300.58%
Quantum Computing (QUBT)	2015-2017	300%
Central Garden & Pet Company A (CENTA)	2015-2017	291.18%
Mercury Systems (MRCY)	2015-2017	280.14%
Extreme Networks (EXTR)	2015-2017	252.68%
Appfolio (APPF)	2015-2017	241.56%
JBTMarel (JBTM)	2015-2017	240.86%
Lantheus (LNTH)	2015-2017	240.83%

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