Jan 8 (Reuters) - Johnson & Johnson and Merck on Monday announced plans to buy cancer therapy developers on the first day of a major U.S. healthcare conference, igniting what industry participants hope will be a strong year for deals after a solid end to 2023.

Deals announced on Monday had a combined equity value of more than $6 billion, including one by medical device maker Boston Scientific for Axonics Inc. That follows roughly $25 billion worth of U.S.-listed biotech deals last month, according to data provider LSEG Deals Intelligence.

Meanwhile, over 8,000 people are gathering at the JPMorgan healthcare conference in San Franscisco, in another sign of a return to business as usual after the COVID-19 pandemic.

Global pharma companies' efforts to replace revenue from older drugs with promising new ones were largely stymied in 2023, but looming patent expirations and easing financing costs are setting up 2024 well, industry sources say.

On Monday, J&J said it would buy Ambrx Biopharma for $2 billion to gain promising targeted cancer therapies known as antibody drug conjugates (ADC).

The deal gets "the ball rolling on what seems to be a strong start for M&A in 2024", said Citi analyst Joanne Wuensch.

Interest in these drugs has spiked and several related companies have been acquired in recent months, including ImmunoGen by AbbVie and Seagen by Pfizer .

Separately, Merck said it would buy cancer drug developer Harpoon Therapeutics for about $680 million, gaining access to early-stage immunotherapies being tested for lung cancer and multiple myeloma.

Boston Scientific's $3.7 billion deal for deal for Axonics helps it enter the market for a type of minimally invasive procedure used in the treatment of overactive bladder and fecal incontinence.

Centerview Partners advised both Harpoon and Ambrx on the deals. Ambrx's financial advisers also included Cantor Fitzgerald.

Evercore Group was Merck's financial adviser, while J.P. Morgan Securities LLC was the adviser to Axonics.

(Reporting by Khushi Mandowara and Sriparna Roy in Bengaluru; writing by Manas Mishra. Editing by Sriraj Kalluvila)