Positive experiment results from its lung cancer drug under development would add value to AstraZeneca's claims that Pfizer's offer is substantially undervaluing it.

AstraZeneca's experimental lung cancer drug, known as AZD9291, which is undergoing an early-stage Phase I trial, shrank tumours in 51% of cancer patients, the company said.

If approved, the drug could generate as much as $3bn in annual revenues for AstraZeneca.

The drug targets a generic gene mutation which causes patients not to respond to current treatments. In the experiment, tumours shrank in 64% patients with the said mutation, which develops in about half of lung cancers.

The phase I trial involved 199 patients with advanced non-small cell lung cancer with gene mutations, whose ailment worsened after treatment with currently available drugs.

The company is conducting a phase 2 study of AZD9291 in patients with mutation with increased daily dosage with a view to accelerate its regulatory filing for the approval of the drug. The US Food and Drug Administration granted "Breakthrough Therapy Designation" to the drug as a second-line therapy for non-small cell lung cancer.

During the 50th Annual Meeting of the American Society of Clinical Oncology (ASCO) at the end of May, AstraZeneca is looking to feature more than 40 scientific abstracts to highlight its strength in the key division.

"We believe that our rich oncology pipeline has the potential to redefine the way that cancer patients are treated. We continue to deliver on our late stage assets and drive our scientific leadership in oncology, as clearly demonstrated by the recent accelerated development of key assets," said Briggs Morrison, chief medical officer at AstraZeneca.

The positive results from the trial would strengthen its cause against a takeover offer from Pfizer.

In its sweetened offer on 2 May, Pfizer valued AstraZeneca at £63bn ($106bn, €77bn) or £50 per share, representing a 32% premium to the company's closing price of £37.82 on 17 April, the last trading date preceding the speculation of an offer.

But the UK company rejected the offer, saying it substantially undervalued AstraZeneca.

Questor said AstraZeneca shares are worth about £100 with three of its cancer drugs in the final stage of testing and another 20 at earlier stages of development.