Shares of ad-tech company The Trade Desk Inc. are down 2.7% in premarket trading Monday after Wells Fargo analyst Peter Stabler lowered his rating on the stock to market perform from outperform. Stabler sees several potential risks ahead for TTD, including "relatively high concentration of spending with a small number of agency holding companies" and a drop in spending on desktop banner-ad placements. "We view TTD's share appreciation (up 89% YTD vs. S&P 500 up 2%) as fully capturing the near-term opportunity," Stabler wrote. He raised his price target on the stock to $88 from $75. TTD shares closed Friday near $87.