Explaining the move, Shire CEO Flemming Ornskov said that "while the oncology business has delivered high growth and profitability, we have concluded that it is not core to Shire's longer-term strategy", which lies mainly in rare diseases.
The firm, which has its headquarters in Dublin, started looking at offloading the oncology business in December, and said the process considered "multiple potential strategic buyers" across Europe, Japan and the US.
Proceeds from the sale is expected to go towards increasing optionality and Shire will consider returning the proceeds to shareholders through a share buyback.
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Still, given the small contribution of the cancer business to Shire's overall profits, Deutsche Bank analysts said this was unlikely to be a deal breaker.
In addition, Takeda Pharmaceutical Co Ltd is still now in the process of considering approaching Shire with an offer to acquire the group, after Nikkei reported earlier in April that Takeda could value Shire at USD55 billion.
Last month, Japanese pharmaceuticals giant Takeda was forced to reveal it was mulling a bid to buy Shire, which boosted the London-listed drugmaker's shares.
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It is positive, as 16 investors sold CZR shares while 29 reduced holdings. 137 funds opened positions while 361 raised stakes. Capital Guardian Trust Co.'s holdings in Kinder Morgan were worth $19,018,000 as of its most recent filing with the SEC.
Shire also had debt of around $19 billion as of the end of 2017. Oncology is therefore a small part of Shire's business, but was highlighted by Takeda as one of three therapeutic categories that could be bolstered by merging the two companies.
Shire has a track record of acquisitions, but its biggest ever deal - the $32 billion purchase of Baxalta in 2016 - was widely criticised by shareholders and has left it struggling to handle debt and integrate its various businesses.
But Monday's news that Shire has sold off its cancer treatment unit - which includes its ONCASPAR (leukaemia) and ONIVYDE (pancreas) treatments - has thrown that possible takeover into doubt.
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The group, which has been working with United Nations Department of Safety and Security, will continue the fact-finding mission. "It is not about regime change", May said in statement made from her country residence at Chequers just minutes after U.S.
"This acquisition allows us to establish a direct commercial presence in the United States, the world's leading pharmaceuticals market, and to strengthen our portfolio of marketed products in the territories where Servier is already present".