Amgen is closing on a deal to acquire Onyx Pharmaceuticals after getting access to data on a key cancer drug , although reports suggest it is reining in the price it is prepared to pay.

Onyx rejected a $120-per-share bid from Amgen valuing the company at around $9.5bn at the end of June, but said it might entertain a higher offer.

Amgen responded with suggestions it might be prepared to go as high as $130 a share, although in return it wanted to take a look at data from ongoing trials of Kyprolis (carfilzomib), a multiple myeloma treatment.

Earlier this week it seemed that access to that data may scupper the deal, but in the last 48 hours it seems access has been granted to Amgen and other interested parties, rumoured to include AstraZeneca. However, the upshot is that Amgen now wants to offer less than $130-per-share, according to Reuters and Bloomberg reports.

The data is thought to relate to the approval of the drug in Europe and also the US, where it was initially given a provisional green light on the condition that Phase III trials back up earlier safety and efficacy data.

Kyprolis is important to the valuation of Onyx as it is the only drug in its portfolio for which it has retained sole marketing rights (with the exception of Japan where it is licensed to Ono Pharmaceutical.

The drug has generated cumulative net sales of $189 million since its approval in July 2012, with Onyx claiming a 40% share of eligible third-line-plus patient population and 10% of the second-line market as the drug gets used in place of older agents and re-treatment with first-line therapies.

Onyx' other products - Nexavar (sorafenib) and Stivarga (regorafenib) for cancer - are licensed to Bayer with Onyx claiming royalty rates in the region of 20% of sales.

The initial overture from Amgen sent Onyx' shares rocketing from a little over $80 to more than $130, although the stock has since retreated to a level of around $120.