AstraZeneca hopes data to be released on several new cancer drugs in the next few days will help justify its decision to turn down a takeover bid from Pfizer.The UK drugmaker's strength in oncology was one of the benefits enticing US-based Pfizer to make a £70bn bid for the group.Pascal Soriot, AstraZeneca Chief Executive, said the company would be better off developing drugs on its own after rejecting the offer, which represented a 45% premium over its share price, according to the Financial Times.The group is now under pressure to drive home Soriot's point on why shareholders would gain more value on AstraZeneca standing alone in developing its drugs. Soriot said a drug called MEDI4736 could produce peak sales of up to $6.5bn. The drug was initially tested as a treatment for a type of lung cancer but has potential to be used on a broader range of tumours.It is among a range of new oncology treatments that make use of the body's immune system to destroy cancer cells. AstraZeneca will reveal more detailed data at the annual conference of the American Society of Clinical Oncologists in Chicago on Tuesday.RD