US stocks hold steady ahead of British vote

NEW YORK (AP) — U.S. stocks are hardly budging Tuesday as investors wait for British voters to decide the fate of that nation's membership in the European Union.

Opinion polls and betting markets indicate that Britons are more likely to vote to remain in the European Union in a referendum Thursday.

Uncertainty about the outcome has weighed on global markets, and polls suggest the result will be close.

Federal Reserve Chair Janet Yellen spoke to the Senate Tuesday and said the U.S. economy faces a number of uncertainties that require the Fed to proceed cautiously in raising interest rates.

[...] trading lower were cancer drug maker Celgene and cystic fibrosis drug maker Vertex.

American Science & Engineering, which makes X-ray inspection systems, agreed to be acquired by airport security and full-body scanner manufacturer OSI Systems Inc. OSI will pay $37 per share, or $263.9 million.

Transportation and logistics company Werner Enterprises forecast disappointing second quarter results.

Used car dealership CarMax disclosed disappointing first-quarter results as its costs increased and sales fell short of Wall Street estimates.

Generic drug maker Impax Laboratories tumbled after it agreed to pay $586 million for a group of generic drugs owned by Allergan and Teva Pharmaceutical Industries.

The parent of United Airlines traded higher as it gave investors new details on how it plans to strengthen its financial performance.

Data security software company Imperva climbed $4.71, or 11.6 percent, to $45.15 after Elliott Capital, the firm run by activist investor Paul Singer, disclosed a stake.