Cidara Therapeutics (CDTX) had the best month in 2015 by a mid-cap US stock in April 2015, returning 1,727.5%.

ASSET	MONTH	% RETURN
Cidara Therapeutics (CDTX)	April 2015	1,727.5%
CleanSpark (CLSK)	May 2015	1,088.11%
Soleno Therapeutics (SLNO)	February 2015	366.67%
Quantum Computing (QUBT)	March 2015	200%
Comstock Resources (CRK)	August 2015	134.61%
Constellium (CSTM)	November 2015	133.16%
Enphase Energy (ENPH)	December 2015	110.18%
Sarepta Therapeutics (SRPT)	May 2015	108.8%
Quantum Computing (QUBT)	February 2015	100%
Quantum Computing (QUBT)	November 2015	100%
Galapagos NV ADR (GLPG)	April 2015	76.04%
Sunrun (RUN)	December 2015	75.67%
Uranium Energy (UEC)	April 2015	73.33%
Travere Therapeutics (TVTX)	March 2015	69.69%
Corcept Therapeutics (CORT)	March 2015	69.18%
Sharplink Gaming (SBET)	February 2015	68.82%
Seabridge Gold (SA)	August 2015	60.8%
Banco Macro SA B ADR (BMA)	October 2015	60.76%
Pampa Energia SA ADR (PAM)	October 2015	59.55%
Skeena Resources (SKE)	July 2015	58.18%
Cleveland-Cliffs (CLF)	August 2015	58.17%
Sharplink Gaming (SBET)	May 2015	57.89%
Companhia Siderurgica Nacional ADR (SID)	April 2015	55.49%
Energy Fuels (UUUU)	December 2015	55.26%
Transportadora de Gas del Sur SA ADR (TGS)	October 2015	54.62%

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