Merck & Co Inc (NYSE: MRK) is reportedly negotiating to purchase cancer drugmaker Harpoon Therapeutics Inc (NASDAQ: HARP) for an estimated $700 million. The move comes as Merck endeavors to diversify its revenue sources, anticipating potential pricing challenges for its flagship drug, Keytruda, an acclaimed cancer immunotherapy that amassed a staggering $20.9 billion in sales in 2022, securing its position as one of the world’s top-selling medications. The proposed acquisition aims to fortify Merck’s dominance in the oncology sector, Bloomberg noted. Discussions suggest that Merck is contempla…