Novartis just paid up to $1.5 billion for Myricx Bio, the last major oncology pharma to enter antibody-drug conjugates. It bought a payload platform, years before it makes a drug.

The first ADC wave bought revenue: Pfizer took Seagen for $43 billion, and the Daiichi deruxtecan deals went to AstraZeneca and Merck. Buyers have claimed most of it, and topo-1 copies crowd the antigens everyone wants, HER2 and TROP2.

So the scarce asset is no longer an ADC. It is a payload outside the topo-1, auristatin, and maytansinoid classes behind most approved ADCs. We mapped every independent developer building one, preclinical to Phase 2, that big pharma has not claimed. The field is 23 companies, most preclinical or Phase 1, with a thin clinical tail.

With Myricx's NMTi payload gone, the open ground is immune-agonist ADCs and clinical-stage cytotoxics. A few are clean buys: Adcentrx's unpartnered Nectin-4 program, Mersana's HER2 STING-agonist, free again after GSK stepped back, and Callio, the best-funded private name. Yet 19 of the 23 carry a diligence flag. The chemistry exists. Owning it outright is the harder question.

The next ADC deal will not turn on the antibody or the target. It turns on the warhead, and the shelf is thinning.