COPENHAGEN (Reuters) - Danish biotech drugmaker Genmab (>> Genmab A/S) expects sales of Darzalex, used to fight cancer in bone marrow, to surpass $1 billion (804.44 million pounds) this year to become a blockbuster drug, the company said on Wednesday.

The strong performance of Darzalex, which is currently approved to treat multiple myeloma, prompted six upward revisions to the company's revenue and operating profit guidance for its 2016 financial year.

The $1 billion a year required to achieve blockbuster is now in sight, with net sales of Darzalex -- approved in November 2015 and is marketed by Johnson & Johnson (J&J) (>> Johnson & Johnson) -- expected to reach between $1.1 billion and $1.3 billion this year, up from $572 million in 2016, Genmab said.

Analyst expectations, on average, are for Darzalex to generate as much as $1.18 billion in revenue this year and $2.53 billion by 2020, according to data from Thomson Reuters Cortellis.

Shares in the Danish company have surged by more than 3,200 percent in the past five years as it has morphed from a cash-burning operation into a profitable business with actual drugs on the market.

Genmab receives tiered royalties from J&J on its sales and expects to receive Darzalex royalties of between 930 million Danish crowns and 1,100 million crowns ($132 million-$156 million) and 800 million crowns in milestone payments this year.

Operating income for 2016 came in at 1.1 billion crowns and is expected in the range of 900-1,100 million crowns in 2017.

With a market capitalisation of $12 billion, Genmab is Europe's second-biggest biotech company behind Actelion (>> Actelion Ltd), although both still lag well behind the likes of U.S. groups Gilead (>> Gilead Sciences, Inc.), Amgen (>> Amgen, Inc.) and Celgene.

However, Genmab's chief executive Jan van de Winkel believes that Darzalex has the potential to achieve peak annual sales as high as $13 billion if the drug is approved for a wider range of cancers.

"It could work in other blood cancers as well as in solid tumours. So that means $13 billion potential if it would work in all the indications," van de Winkel told Reuters.

He acknowledged that $13 billion would be the most rosy scenario but said that Darzalex could "definitely" achieve more than $9 billion.

($1 = 7.0497 Danish crowns)

(Reporting by Stine Jacobsen; Editing by Elaine Hardcastle and David Goodman)