US shares have opened modestly lower, appearing prone to taking a breather for a third session after last week’s strong run-up.

But biotech shares got a boost from Vertex Pharmaceuticals (+47.2 per cent) after it reported promising results in tests of two drugs for treating cystic fibrosis.

Five minutes into trade, the Dow Jones Industrial Average was down 20.77 points (0.12 per cent) to 16,916.49.

The broad-based S&P 500 slipped 3.06 (0.16 per cent) to 1,959.55, while the tech-rich Nasdaq Composite gained 2.17 (0.05 per cent) to 4,370.85.

“By and large, markets look to be consolidating some of their recent gains as the end of the second quarter approaches,” said Patrick O’Hare of Briefing.com.