Pfizer drops 4%, leading Dow lower

BOSTON (MarketWatch) -- Shares of Pfizer Inc. , a component of the Dow Jones Industrial Average , dropped 4% to $19.58 in afternoon trading Thursday amid reports that four patients had died in a key clinical trial. According to the Wall Street Journal, a European medical website posted data from a study for Pfizer's rheumatoid arthritis drug tofacitinib that indicated four of the participants ...