LONDON (Reuters) - AstraZeneca (>> AstraZeneca plc) said on Monday it was in talks that might lead to the acquisition of privately held biotech firm Acerta Pharma, a potential $5 billion-plus (3.29 billion pounds) deal designed to build up its cancer drug portfolio.

"AstraZeneca confirms that it is exploring potential strategic options with Acerta Pharma BV. There can be no certainty that any transaction will ultimately be entered into, or as to the terms of any transaction," it said in a brief statement.

The Wall Street Journal had reported on Friday that the British drugmaker was looking to buy Acerta for more than $5 billion to gain access to its experimental blood cancer drug acalabrutinib.

Acalabrutinib works in a similar way to Imbruvica, which was developed by Pharmacyclics but is now controlled by AbbVie (>> AbbVie Inc) after the U.S. drugmaker bought Pharmacyclics for $21 billion earlier this year.

Both drugs target an array of blood cancers and have the potential to become multibillion-dollar-a-year sellers, according to industry analysts.

Given pharmaceutical companies' current heated interest in oncology, Bernstein analyst Tim Anderson said it was not surprising that Acerta, based in California and the Netherlands, was an acquisition candidate.

It does not yet have a partner to help develop its leading drug, although it has agreed to test acalabrutinib in combination with Merck's (>> Merck & Co., Inc.) Keytruda.

Acerta is running a wide range of cancer clinical trials, including two final-stage Phase III studies. Last week it reported positive results in leukaemia.

The decision to chase after Acerta reflects a determination by AstraZeneca Chief Executive Pascal Soriot to use deals to boost his company's pipeline as sales of older blockbusters, including cholesterol fighter Crestor, lose patent protection.

Last month he agreed to buy ZS Pharma (>> ZS Pharma Inc), a specialist in treating high potassium levels, for $2.7 billion.

But the biggest hopes are pinned on oncology, where AstraZeneca already has a goal of bringing six new cancer treatments to market by 2020.

Its new lung cancer pill Tagrisso, which it believes could sell $3 billion a year, was approved last month and the company also recently launched Lynparza for ovarian cancer.

Buying Acerta would take AstraZeneca into the less familiar territory of blood cancers and some analysts said the move suggested a bigger commitment to this area of oncology than initially expected.

Earlier this year AstraZeneca signed a deal to co-develop another cancer drug, durvalumab, in blood cancers with Celgene (>> Celgene Corporation) because it said at the time it had limited experience in the field.

(Editing by Mark Potter and Keith Weir)

By Ben Hirschler