Genmab shares doubled in three months and surged 48% last week after the Danish biotech reported three successful Phase 3 cancer trials in October. The company's stock jumped 29% in a single session following positive results for petosemtamab, its experimental head and neck cancer treatment combined with Merck's Keytruda, which reduced death risk by 50% versus Keytruda alone.

The trial wins also included Rina-S, which cut disease progression or death risk by 71% in ovarian cancer, and Epkinly, co-developed with AbbVie, which reduced progression or death risk by 51% in lymphoma when combined with chemotherapy.

Genmab, valued at roughly $35 billion, has historically earned royalties from drugs it helped develop, including Johnson & Johnson's Darzalex (expected to generate $16.5 billion to $16.9 billion in sales this year, with Genmab receiving up to 20% royalties) and Novartis' Kesimpta. CEO Jan van de Winkel told CNBC the breakthroughs marked "a completely new era" as the company shifts to retain larger revenue shares from its own treatments.

Genmab acquired petosemtamab through an $8 billion purchase of Merus in 2025 and Rina-S through a $1.8 billion acquisition of ProfoundBio in 2024. The company borrowed $5.5 billion to help fund the Merus deal. Van de Winkel stated petosemtamab could become a "multi-billion dollar drug." Jefferies analysts estimated petosemtamab could generate $3.5 billion in peak annual sales treating recurrent or metastatic head and neck cancer, with expansion into locally advanced disease potentially adding another $3.5 billion.

Genmab now operates 15 Phase 3 trials across its three lead compounds and aims for majority-owned medicines to reach around 500,000 patients by the 2030s, up from fewer than 30,000 today. Van de Winkel acknowledged geopolitical shifts and drug-pricing pressures could complicate expansion plans.

Investors in Genmab shares should monitor third-quarter earnings due Nov. 5 and regulatory pathways for petosemtamab, Rina-S, and Epkinly as the company transitions to greater commercial ownership of its pipeline.