Genmab (GMAB), on Monday, announced its plan to buy cancer-focused biotech company Merus (MRUS) for about $8 billion. The news sent Merus stock into the stratosphere. Its most advanced program is in head-and-neck cancer, but Merus is also testing the drug in patients with metastatic colorectal cancer. Petosemtamab could generate $3 billion to $4 billion in peak sales in head-and-neck cancer alone, William Blair analyst Matt Phipps said in a report. In early trades on today's stock market, Merus stock catapulted more than 36% to 94.