Two drug companies say an experimental breast cancer drug shrank tumors in half of a small group of patients whose cancer had already been treated with Enhertu, one of the most widely used drugs for this disease. LigaChem Biosciences and its partner Iksuda Therapeutics announced the early results on November 2, 2026, for a drug called IKS014, also known as caxmotabart entudotin1.
Five of 10 patients with HER2-positive breast cancer that had spread through the body had what doctors call a partial response, meaning their tumors shrank but did not disappear1. One of those responses has lasted more than 18 months, and a sixth patient’s cancer held steady1. The results are early, small and come from the companies, not from a published paper.
What happened
The numbers come from an interim look at a Phase 1 study, the first stage of testing in people, which mainly checks safety and dosing1. The drug was given on its own1.
The patients had been through a lot of treatment. They had received a median of six earlier lines of therapy, ranging from two to 121. All of them had previously received Enhertu (trastuzumab deruxtecan)1.
The analysis used data collected up to April 20261. The companies plan to present updated results, including patients enrolled since then, at the San Antonio Breast Cancer Symposium on December 9, 20261.
Why patients after Enhertu are a hard group to treat
HER2-positive breast cancer, where cancer cells make too much of a protein called HER2, affects roughly 15% to 20% of people with breast cancer2. Enhertu, made by AstraZeneca and Daiichi Sankyo, is approved in more than 100 countries for patients with spread HER2-positive breast cancer who have already had another anti-HER2 treatment, and it has become the usual second treatment, according to Tech Times1. In the United States it is also approved as a first treatment for spread HER2-positive breast cancer when given with another drug, pertuzumab, and for some patients with earlier-stage disease3. That first-treatment use follows a large trial of 1,157 patients that compared the Enhertu combination with the older standard2.
As Enhertu is used more widely and earlier, more patients will eventually see their cancer grow despite it, and there is currently no established next step for them, Tech Times reported1. Earlier attempts in this group have gone poorly:
- A look back at patient records at MD Anderson Cancer Center found that Kadcyla (trastuzumab emtansine), an older HER2-targeted drug, produced no tumor responses in 21 patients who had already had Enhertu. Their cancer was held in check for a median of just 2.2 months1.
- A forward-looking trial called SATEEN, which combined Trodelvy (sacituzumab govitecan) with trastuzumab, saw one response in 27 patients (3.7%). It was stopped early for falling short of its efficacy goal, and one patient died of a severe infection linked to low white blood cell counts1.
SATEEN’s lead investigator, Paolo Tarantino of Dana-Farber Cancer Institute, has said there is no forward-looking data to guide treatment after Enhertu stops working1. He said the SATEEN results:
help clarify treatment expectations after T-DXd and reinforce the importance of developing new approaches
How the drug is meant to work
Enhertu, Kadcyla and IKS014 belong to a family called antibody-drug conjugates. Each uses an antibody that latches onto the HER2 protein on cancer cells and carries a toxic “payload” inside1.
The difference is in the payload. Enhertu’s cargo, called deruxtecan, blocks an enzyme called topoisomerase I that cells need to unwind their DNA when copying it; when it is blocked, the cell dies1. Trodelvy, used in SATEEN, carries a cargo from the same class1. Tech Times explained that if a cancer has adapted to resist Enhertu’s cargo, the same resistance may already be in place when a drug with a similar cargo arrives1.
IKS014 carries a different cargo, called MMAF (monomethyl auristatin F). It does not act on topoisomerase at all. Instead it binds to tubulin, the building block of the fibers a cell uses to pull its copied chromosomes apart when it divides. Without those fibers, the cell stalls partway through division and dies1. The drug was built using LigaChem’s own linking technology, called ConjuALL1.
Tech Times described the result as the strongest sign yet that switching to a different type of cargo, not just targeting HER2 again, could shape treatment after Enhertu1. That is the outlet’s interpretation; the data so far are too limited to settle it.
What the result does not show yet
Several limits matter here:
- Very few patients. The 50% figure rests on 10 patients1. With numbers this small, one or two patients more or less would change the percentage a lot.
- No comparison group. Every patient got the new drug. The lower response rates for Kadcyla and the Trodelvy combination come from different studies, with different patients, so the numbers cannot be compared directly1.
- Not yet published. The figures come from a company announcement, as reported by Tech Times, not from a peer-reviewed paper1.
- No survival data. Tumor shrinkage is an early measure. The results reported so far do not show whether patients live longer or live better.
- Side effects not described. The sources available to Biohack did not report details on the drug’s side effects in this group, which is the main purpose of a first-stage study.
- Older data cut. The analysis used data up to April 2026, so the picture may change with the update due in December1.
Who is behind it
IKS014 is developed by LigaChem Biosciences, whose ConjuALL technology the drug is built on, together with its partner Iksuda Therapeutics1. The two companies announced the results themselves1. Both stand to gain if the drug moves forward, which is common for early drug results and a reason to wait for independent review and fuller data.
Enhertu, the drug these patients had already received, is sold by AstraZeneca and Daiichi Sankyo1. Background on Enhertu’s approved uses in this article comes partly from its makers’ patient website3.
What to watch next
The next checkpoint is December 9, 2026, when updated results with more patients are scheduled at the San Antonio Breast Cancer Symposium1. Key questions for that update:
- Whether the share of patients whose tumors shrink holds up as more people are added.
- How long responses last across the group, not just in the one patient past 18 months.
- What side effects patients had, and how often.
- Whether the companies announce a larger, controlled trial in patients whose cancer has grown after Enhertu.
For now, the result is an early signal in a small group of heavily treated patients, in a setting where doctors say there is no established next step1. Whether it turns into a useful treatment depends on larger studies that have not yet been reported.
