Small-cap stocks strayed far behind the sliding major indices Tuesday, and one of the worst performers was Inovio Biomedical ( INO). The San Diego-based company plummeted 36% to $2.20 after halting patient enrollment in both of its late-phase pivotal studies on an investigational therapy called selective electrochemical tumor ablation (SECTA). An independent data-monitoring committee noted, among other things, that the mortality rate among the head- and neck-cancer patients treated with SECTA was higher than among those who underwent surgery. Shares of North American Scientific ( NASI), which likewise makes cancer-treatment products, slid 18% to $1.23 after the California-based company's second-quarter revenue fell 22.9% year over year to $6.2 million, even though per-share losses halved to 11 cents. Women's apparel retailer Cache ( CACH) sank 12.2% after it slashed guidance for the rest of the year to fall far short of Wall Street expectations. Cache shares fell $1.98 to $14.26 and weighed on the Russell 2000 index, which recently gave up 0.8% at 848.27. Internet-protocol-video semiconductor Sigma Designs ( SIGM), another Russell 2000 member, tumbled 8.3% after an analyst with American Technology Research maintained his sell rating on the stock. He cited the company's predicted slowdown in sequential sales growth, which he attributes to mounting customer pressure on Internet-protocol TV pricing, as well as "looming" competitive threats. Despite positive results for the most recent quarter, Sigma shares lost $2.40 to $26.68.