Merck & Co said on Monday it would buy cancer drug developer ArQule Inc in a $2.7 billion all-cash deal, bolstering its oncology franchise with the smaller rival's lead drug that is being tested as a treatment for blood cancer. The offer of $20 per share for ArQule is more than double its closing price on Friday. The deal, expected to close early in the first quarter of 2020, would give Merck access to ArQule's experimental treatment ARQ 531, a precision medicine that tailors treatment to a patient's genetic profile. Merck's blockbuster cancer immunotherapy Keytruda topped $3 billion in sales in the latest quarter.While Keytruda has become Merck's most important growth driver, racking up U.S. approvals to treat numerous types of cancer since it was first approved for advanced melanoma in 2014, analysts have called for the company to reduce its reliance on a single product. ArQule shares rose to $19.32 before the bell.