That amounts to €1.98bn, which is $72 (€49.1) per Pharmion share, which is a hefty mark-up on its Friday closing price of $49.28. However, analysts seem to agree that the two company's drugs will sit well with each other and Celgene has got its money's worth.

A large part of Celgene's oncology franchise consists of thalidomide and derivatives of that molecule, such as Revlimid (lenalidomide). These are approved to treat multiple myeloma (MM) and myelodysplastic syndromes (MDS).

With this latter group of conditions, the bone marrow typically produces more blood cells than normal, yet they are defective, leading to lower numbers in circulation. In some cases, this can lead to acute myeloid leukaemia (AML).

Although Celgene has four immunomodulatory drugs, dubbed 'IMiDs', in its pipeline, they treat MDS, not AML. This is where Pharmion comes in, with its drug called Vidaza (azacitidine). The injection form of the drug is already approved to treat MDS, but crucially, is also in Phase II trials for AML. An oral form is also in Phase I clinical trials for both diseases (see table below).

"It's a great move for Celgene," Michael King, an analyst with Rodman & Renshaw, told Bloomberg.

"Vidaza has the potential to be a billion-dollar product."

He went on to explain that Celgene probably plan to use Revlimid for less advanced MDS and then switch patients to Vidaza after they develop resistance. Pharmion has also previously said it expects to submit a Market Authorization Application (MAA) in Europe for Vidaza in higher-risk MDS before the end of the year.

Both US companies also have thalidomide drugs approved. In fact, Pharmion licensed it from Celgene for development and commercialisation in Europe and other selected countries.

"The combination of our two product portfolios and organisations represents the opportunity to create a leading global haematology/oncology company," said Patrick Mahaffy, CEO of Pharmion.