Cancer treatment specialist BeiGene Ltd plunged 16.4% on its Shanghai debut on Wednesday after raising $3.5 billion, hit by concerns over its valuation amid potential US sanctions on Chinese biotech companies. BeiGene , which is already listed in Hong Kong and the United States, launched the biggest STAR Market float this year, taking advantage of rules by the Nasdaq-style board which welcomes loss-making firms. Shares in BeiGene , which plans to use the majority of the proceeds to fund clinical trials and has posted at least three consecutive annual losses, closed 16.4% lower than its offer price of 192.6 yuan…