Stock futures showed narrow gains Tuesday, as a quiet economic calendar left the focus on earnings reports and the presidential election. Dow futures traded up 22 points. Nasdaq 100 futures were 11.75 higher and S&P 500 futures rose 4.3 points. Despite the hush on the overall market, leading stocks were highly active in premarket trade. 3D SystemsDDD and Bonanza Creek Energy (BCEI) were among those to gain 3% or more. Express Scripts (ESRX)