Pfizer, AstraZeneca, Merck bet on chemo replacement

Chemotherapy has long been a cornerstone of cancer treatment, saving millions of lives.

But the pharmaceutical industry says a popular class of targeted cancer therapies could one day replace chemotherapy and its potential for harsh side effects in some cases. Antibody-drug conjugates (ADCs) have taken major strides in recent years, as companies including AstraZeneca, Daiichi Sankyo, Pfizer and Merck are developing drugs in the space that could ease the trials of cancer treatment and make them big money in the process.

Drugmakers have poured billions of dollars into developing ADCs. The medicines are designed to deliver potent chemotherapy directly to cancer cells while sparing surrounding healthy cells. That’s unlike traditional chemotherapy, which can affect both types of cells.

But it will likely take years before ADCs can replace chemo more broadly, and some outside cancer experts say the pharmaceutical industry still has more work to do to refine the treatments.

“I think we’ve had some successes in the space, but I think the early hopes that they would sweep away the need for chemotherapy have mostly been unfulfilled so far,” Dr. John Heymach, chair of thoracic/head and neck medical oncology at MD Anderson Cancer Center, told CNBC. “There’s clearly room for improvement.”

Still, some companies say ADCs have shown the ability to replace chemotherapy in certain settings. Other drugmakers say they are inching closer to developing ADCs that can be used before chemo — or at the very least, learning from previous missteps.

“We are leading the way towards establishing ADCs as a precision-based approach to replace classic chemotherapy,” David Fredrickson, executive vice president of AstraZeneca‘s oncology business, told CNBC. 

He was in part referring to AstraZeneca’s promising data shared at the 2025 American Society of Clinical Oncology annual meeting in Chicago, where several other companies also delivered positive results on existing and experimental ADCs – or even data that could lead to new standards in cancer care.

Since the first ADC hit the market in 2000, the field has made major progress. More than a dozen ADCs are now approved in the U.S., and some have become a preferred or commonly used treatment option for specific tumors. Hundreds more ADCs are in development. Large pharmaceutical companies have scooped up many of the approved and experimental ADCs in massive deals, such as Pfizer‘s $43 billion acquisition of Seagen in 2023.

A range of drugmakers want in on the hype, and for good reason. ADCs could account for $31 billion of the $375 billion worldwide cancer market in 2028, according to estimates from the drug market research firm Evaluate.

ADCs still pose major challenges. Among them, some treatments can release the toxic chemotherapy “payload” into the bloodstream too soon, affecting healthy cells and causing a range of side effects. Some health experts say drugmakers also need to identify the right cancer-causing proteins to target and new payloads for these drugs.

The pharmaceutical industry is working to overcome these issues by developing next-generation ADCs and combination regimens. Some ADCs, such as a newly approved therapy from AbbVie, target new proteins, while others use new so-called linker platforms that better control when and where the toxic payload is released.

“It’s been hard. We haven’t optimized everything perfectly yet. But I think that the field is still growing fast, and it’s making improvements every year,” said Dr. Jeffrey Infante, global head of early clinical development, translational research and oncology at Johnson & Johnson, which has several experimental ADCs.

Most ADCs consist of three components: an antibody that targets a protein found in high amounts on the surface of cancer cells, a chemotherapy payload and a linker that connects them. The antibody guides the ADC to the cancer cell, and once inside, the linker releases the chemotherapy to kill the cancer from within.

Newer ADCs leading the space, such as Enhertu from AstraZeneca and Daiichi Sankyo, improve on that design and are moving closer to becoming standard treatments for certain cancers.

Enhertu delivers more chemotherapy per dose than older ADCs and uses a smart linker designed to release the drug only inside tumors. It can also kill nearby cancer cells with lower levels of HER-2, the protein it targets – a major milestone in oncology. 

Enhertu is approved in the U.S. to treat certain breast, lung and gastric cancers, with 2024…