AstraZeneca (AZN.L) shares gained 2 percent in early trading on Thursday on speculation that U.S. drugmaker Pfizer (PFE) was about to return with a higher bid worth more than 53 pounds a share, traders said. Pfizer’s previous approach, which was promptly rejected by the AstraZeneca board, initially valued the group at $106 billion – but the value of that cash-and-stock offer has since slipped because of a fall in Pfizer shares following weak quarterly results.