Big-cap stocks like Nvidia (NVDA) and Palantir (PLTR) steal much of the attention. But now investors are scoring massive gains on small caps not in the S&P 500.Seven small stocks in the iShares Russell 2000 ETF (IWM), including cancer treatment company The Oncology Institute (TOI), mortgage firm Better Home & Finance (BETR) and used apparel seller ThredUp (TDUP), jumped more than 400% this year, says an Investor's Business Daily analysis of data from S&P Global Market Intelligence and MarketSurge.What's Hap ...