According to people familiar with the matter, a bid from J&J is expected to value Pharmacyclics at a premium to its current $17 billion market capitalization and could be agreed in coming days. These people warned that the talks have not been finalized and may still fall apart.
Shares in Pharmacyclics were up 6.7 percent in late US trading on Wednesday,
A deal would follow years of extensive collaboration between New Jersey-based J&J and California-based Pharmacyclics in developing a drug to treat blood cancer.
The duo won expanded approval from US health regulators in late January for a breakthrough drug called Imbruvica, which helps fight a rare form of cancer that begins in the body's immune system.
The transaction would be the biggest for J&J since it struck a deal to acquire specialized surgical device maker Synthes for $21.3 billion in 2011.
It would also come as a wave of innovation in developing treatments to rare, orphan or hard to treat diseases is leading to steep competition among large healthcare companies to acquire leading labs that have specific, specialized treatments.
Shares in Pharmacyclics have risen more than 88 per cent since the start of the year, prompted in part by speculation that it was weighing interest from suitors such as J&J. The company had a market capitalization of $17 billion on Wednesday, compared with $282 billion for J&J.
A deal would be the latest large scale transaction this year in a sector where deal making remains extremely active. Since the start of the year, Valeant has acquired gastrointestinal drugmaker Salix for $14.5 billion, Pfizer bought medical device maker Hospira for $17 billion and the UK's Shire picked up NPS Pharma for $5.2 billion.