Could metastatic HER2+ become a long-term remission?

8 hours ago

6 min read

A promising therapeutic HER2 vaccine is producing an immune response in early human testing. Here’s what we know so far, and what we don’t.

I’m always looking for what’s coming next.

Anything that might mean more time, longer remission and, one day, hopefully, a cure.

As someone living with HER2 positive metastatic breast cancer, research like this isn’t abstract to me. When I read about a new drug, vaccine or clinical trial, I’m reading it with one very personal question in the back of my mind:

Could this one day matter for people like me?

One study I’ve been following is ES2B C001, an experimental therapeutic HER2 vaccine currently being studied in a first in human Phase I clinical trial.

And the early immune response data are interesting.

First, this isn’t a vaccine to prevent breast cancer

When we hear the word vaccine, most of us think about preventing a disease before it happens.

Cancer vaccines can work differently.

ES2B C001 is being investigated as a therapeutic vaccine. This means it is being studied in people who already have cancer, with the aim of stimulating the immune system to recognise HER2 and mount an immune response against it.

That distinction matters.

This isn’t about preventing HER2 positive breast cancer from developing. It is about asking whether the immune system can be trained to recognise a target already present on cancer cells, and whether that immune response might eventually translate into meaningful control of the disease.

So what has happened so far?

In the preliminary Phase I data I shared in September, 12 of 13 evaluable participants developed anti HER2 antibodies.

Even more interestingly, all five of the five patients who had completed the vaccination schedule developed an immune response, with a reported median peak increase of approximately 16 fold in anti HER2 antibodies.

Those numbers caught my attention.

But there is a very important distinction to make.

An immune response is not the same thing as proving the vaccine controls cancer.

At this early stage, the findings tell us that the vaccine appears capable of doing something researchers hoped it would do. It can provoke an immune response against HER2.

They do not yet establish that it shrinks tumours, delays progression, extends survival or produces long term remission.

And that is why this is promising, but still very early.

Why does this research matter?

HER2 positive metastatic breast cancer has already been transformed by targeted therapies.

The question now is whether immunotherapy and vaccines could eventually add another tool.

The idea is compelling. Rather than relying solely on treatments that directly target cancer cells, could we also teach the body’s own immune system to recognise HER2 and maintain an attack against cells expressing it?

That opens up several possibilities researchers can investigate in later trials.

Could a vaccine help maintain disease control for longer?

Could it work alongside established HER2 therapies?

Could it eventually contribute to longer periods of remission?

Could some patients ultimately require less treatment?

And, much further down the road, could immune based approaches become one piece of what turns metastatic HER2 positive breast cancer into a disease capable of extremely long term remission, or even cure?

We don’t know yet.

That’s the part I think is important to say just as loudly as the exciting part.

How this fits into the bigger picture

ES2B C001 isn’t happening in isolation.

Researchers around the world are investigating different ways of stimulating the immune system to recognise HER2.

There are peptide vaccines, dendritic cell vaccines, mRNA approaches, personalised cancer vaccines and other immune strategies being explored.

Some are designed for people with existing cancer. Others are being investigated in earlier stages or to reduce the risk of recurrence. Some may eventually be combined with existing HER2 therapies.

For me, that is what makes this entire field worth watching.

Not because one early Phase I result suddenly means we’ve found a cure.

We haven’t.

It’s because researchers are continuing to attack the same disease from different directions, with better targeted treatments, antibody drug conjugates, immune therapies, vaccines and combinations of them.

Each approach potentially gives us another way of keeping the cancer under control.

Could this be relevant to metastatic disease?

This is one of the reasons this particular research caught my attention.

ES2B C001 is being studied as a therapeutic strategy in people with advanced HER2 expressing cancer. It isn’t simply a vaccine designed to prevent recurrence in people with early stage disease.

That makes this research particularly interesting to those of us already living with metastatic HER2 positive breast cancer.

It still doesn’t mean the vaccine will ultimately work for metastatic breast cancer, or for any particular site of metastatic disease.

Those questions require substantially more clinical data.

But it means this isn’t research I have to look at from the sidelines and think, that’s wonderful, but it’s only for early stage disease.

And personally, that matters to me.

What happens next?

Phase I studies are deliberately small.

Their job is not to prove that a new treatment extends life.

Researchers first need to establish whether it is sufficiently safe, determine appropriate dosing, understand the immune response and look for early signs that justify taking the treatment into larger studies.

Full Phase I results have been expected around the end of 2026, with a Phase II study previously targeted for the second half of 2027.

If the findings remain encouraging, larger and longer studies can begin answering the questions patients really want answered:

Does it actually control the cancer?

For how long?

Does it delay progression?

Does it help people live longer?

And which patients benefit?

Those are much bigger questions than whether antibodies appear in a blood test.

They also take much longer to answer.

What could this eventually mean for patients?

The hope is not simply to produce antibodies.

The bigger goal is meaningful clinical benefit.

If therapeutic vaccines eventually prove effective, researchers could investigate whether they might help the immune system keep cancer under control for longer, work alongside existing HER2 treatments, delay progression or perhaps contribute to longer periods of remission.

The possibility of reducing treatment burden is also interesting.

For people living with metastatic cancer, treatment is generally ongoing. So the possibility that immune based approaches could one day help maintain cancer control with less continuous treatment is something worth investigating.

And then there is the question that matters enormously to those of us living with metastatic disease.

Could approaches like this eventually contribute to a cure?

At the moment, there simply isn’t enough evidence to say that.

But that is precisely why the next stages of research matter.

What I take from this

I try to hold two things at once when I read cancer research.

Hope and perspective.

Twelve out of thirteen people developing anti HER2 antibodies is encouraging.

Five out of five people who completed the vaccination schedule developing an immune response is encouraging.

But thirteen people is thirteen people.

It is a signal worth following, not proof of a cure.

For those of us living with metastatic breast cancer, I think there is something genuinely hopeful in watching science continue to move beyond simply asking how we treat this disease, toward questions about immune control, durable remission and entirely new ways of attacking it.

I don’t know whether ES2B C001 will ultimately be one of the answers.

Nobody does yet.

But it is one I will keep watching.

I’ll keep doing the digging, reading the research and sharing the developments I think matter most to those of us living with HER2 positive metastatic breast cancer.

Because when you’re living with an incurable cancer, what’s coming next matters.

Important to know

This is early research involving small numbers of participants.

An antibody response does not establish that a vaccine shrinks cancer, prevents progression, extends survival or produces a cure.

Experimental HER2 vaccines do not replace established HER2 treatments. Anyone interested in participating in a clinical trial should discuss their individual circumstances and treatment with their oncology team.

There is still a long way to go.

But these early results give us something worth watching.

And for now, that is reason enough for hope.

Sources & further reading

ES2B C001 Phase I clinical trialOfficial European clinical trial registry entry for the first in human ES2B C001 study in HER2 expressing metastatic breast cancer.View the EU Clinical Trials Registry record →

ES2B C001 preliminary Phase I results, August 2026The August 2026 update reporting anti HER2 antibody responses in 12 of 13 evaluable patients, responses in all five patients who had completed dosing, a median 16 fold peak antibody increase, and no dose limiting toxicities reported at that data cut. Nasdaq News ViewerRead the August 2026 Phase I update →

ES2B C001 vaccine overviewExpreS2ion's overview of the vaccine, its VLP technology, HER2 target and current stage of clinical development.Read about ES2B C001 →

HER2 therapeutic vaccine research, 2026A peer reviewed paper in npj Vaccines examining the HER2 therapeutic vaccine approach and its use alongside HER2 monoclonal antibody treatment. NatureRead the research in npj Vaccines →