Wall Street stocks retreat, oil tumbles on oversupply concerns

By Hilary Russ NEW YORK (Reuters) - Wall Street stocks retreated on Wednesday led by health care and materials stocks, while oil prices tumbled about 3.0 percent on worries about oversupply. Mylan slumped 5.4-percent to $43.15 after U.S. presidential candidate Hillary Clinton joined a Senate committee in asking why the cost of its allergy treatment EpiPen had soared. Gold fell to a one-month low as the U.S. dollar firmed and markets looked ahead to a speech by Federal Reserve Chair Janet Yellen