European stocks pause after third week of gains

(Reuters) - European shares retreated on Friday, led by healthcare and media companies, at the end of a third week of gains dominated by signs that the world's big central banks are on the verge of another round of action to support growth.Traders said many investors had been tempted to cash in some of this month's around 4% gain, encouraged by escalating tensions between Washington and Iran, and the pan-regional STOXX 600 index ended 0.4% lower.It was also a day of "triple witching" where..