Although it took a while, targeted cancer drugs lived up to the hype

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how to do it in a manner that could make them a staple of cancer care. That’s reflected in pharma companies’ sudden deep commitment to the space. In addition to AbbVie’s acquisition, other deals this year include Pfizer’s proposed $43 billion buyout of Seagen, Merck & Co’s $4 billion tie-up with Daiichi Sankyo, and a series of smaller investments from Bristol-Myers Squibb and Eli Lilly & Company.

It has taken a while to get here. ImmunoGen has been at its smart-bomb technology for longer than some biotech executives have been alive. Formed in 1981, the company has survived many peaks and valleys in its pursuit of antibody-drug conjugates.

At one point, it had chugged along so long that one New York Times reporter included it in a list of “zombie biotechs"—companies churning through cash for decades without ever turning a profit. While a drug developed by one of its partners that used its technology was approved in 2013, ImmunoGen didn’t have its own product on the market until last year. But the slog has finally paid off.

Scientists seem to have determined the right design for making the drugs sufficiently safe and highly effective. That’s something of an art that involves picking the right antibody to home in on a cancer cell and settling on the right type of chemotherapy to knock it out. The most vexing piece, though, has been engineering the link between those two parts—one that holds tight while the drug circulates in the blood but releases when it reaches a tumour.