Quantum Computing (QUBT) had the best month between 2013 and 2014 by a mid-cap US stock in February 2013, returning 566.7%.

ASSET	MONTH	% RETURN
Quantum Computing (QUBT)	February 2013	566.67%
Quantum Computing (QUBT)	April 2013	242.86%
Applied Digital (APLD)	February 2014	200%
Centrus Energy (LEU)	July 2013	174.48%
Green Brick Partners (GRBK)	March 2014	151.73%
Plug Power (PLUG)	May 2013	137.5%
Aris Mining (ARMN)	February 2014	126.14%
Camtek (CAMT)	November 2013	125.82%
Plug Power (PLUG)	December 2013	106.67%
NexGen Energy (NXE)	February 2014	101.41%
Quantum Computing (QUBT)	May 2014	100%
Leonardo DRS, Inc Common Stock (DRS)	September 2014	98.67%
Applied Digital (APLD)	February 2013	92%
Centrus Energy (LEU)	July 2014	86.56%
Arrowhead Pharmaceuticals (ARWR)	July 2013	85.71%
Frontline (FRO)	December 2014	83.21%
Aura Minerals Inc Common Shares (AUGO)	February 2014	81.02%
Cytokinetics (CYTK)	January 2013	76.12%
RadNet (RDNT)	April 2014	73.17%
Applied Opt (AAOI)	February 2014	72.7%
Cytokinetics (CYTK)	December 2014	72.26%
Globalstar, Inc Common Stock (GSAT)	January 2013	71.88%
Amicus Therapeutics (FOLD)	August 2014	71.6%
Travere Therapeutics (TVTX)	February 2014	68.29%
Globalstar, Inc Common Stock (GSAT)	September 2013	67.69%

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