Avelumab (Bavencio) — PD-L1 immunotherapy for Merkel cell carcinoma and bladder cancer

What is avelumab (Bavencio) in simple words

Avelumab (Bavencio) — a drug that works through the immune system rather than attacking cancer cells directly.

It belongs to a group called PD-L1 inhibitors. Tumours use a surface protein to suppress immune cells and avoid detection. Avelumab blocks that protein. The immune system gets a chance to respond.

Two situations where this drug is used. First — Merkel cell carcinoma, a rare aggressive skin cancer. Second — bladder cancer, but only as maintenance after chemotherapy has already done its work. These are different diseases with different logic behind the treatment.

How avelumab works

A surface protein on tumour cells sends a suppression signal to immune cells — essentially telling them to stand down. Avelumab blocks that protein. The signal stops. Immune cells regain the ability to recognise and attack the tumour.

Avelumab also engages natural killer cells — a part of the immune system capable of destroying cancer cells directly. Whether this gives it a meaningful clinical edge over other drugs in the same class is still being studied.

What is established is where it works. And for this drug, Merkel cell carcinoma is that place.

What conditions avelumab is used for

Avelumab is approved for two indications:

• Merkel cell carcinoma — locally advanced or metastatic;

• bladder cancer — maintenance therapy after platinum-based chemotherapy, in patients whose disease did not progress during treatment.

Merkel cell carcinoma is where this drug made its clearest mark. Before immunotherapy arrived in this space, systemic treatment options were limited and responses did not last. Clinical trial data showed that avelumab produced responses that held up considerably longer. That was the basis for its approval — and subsequent data in treatment-naive patients added further confidence.

In bladder cancer, the indication is narrower. Trial data showed that patients who continued on avelumab after responding to platinum chemotherapy had better survival outcomes than those who moved to observation. That is the clinical rationale.

Even the same diagnosis can lead to different decisions. Stage, biomarker profile, prior treatment and the patient’s condition all determine whether this is the right choice at a given moment.

When avelumab may be especially relevant

It tends to come up in these situations:

• Merkel cell carcinoma that has spread beyond surgical or radiation control;

• locally advanced Merkel cell carcinoma not amenable to local treatment;

• bladder cancer that remained stable or responded during platinum chemotherapy;

• patients with Merkel cell carcinoma who have exhausted local options.

The bladder cancer indication has a specific requirement. Avelumab maintenance is only for patients whose disease held stable or improved on chemotherapy. If the cancer grew — this approach does not apply. A different strategy is needed. I always confirm what actually happened during chemotherapy before any maintenance conversation.

Merkel cell carcinoma is also associated with a virus in some cases. Both virus-positive and virus-negative tumours respond to avelumab, though early data suggested slightly different patterns between the groups. Virus status does not change eligibility.

What needs to be checked before starting treatment

Before avelumab is seriously considered, the oncologist will typically review:

• biopsy and pathology — confirmed histology is essential in Merkel cell carcinoma;

• disease staging and current extent;

• full prior treatment history and how the cancer responded;

• whether bladder cancer progressed on platinum — if yes, maintenance is not appropriate;

• kidney and liver function;

• thyroid status;

• autoimmune history;

• performance status.

Histological confirmation in Merkel cell carcinoma deserves special attention. This cancer can resemble other small round cell tumours on initial biopsy. Specific immunohistochemical markers are needed to distinguish it. I have seen treatment started on the wrong diagnosis. It is avoidable — but only if the pathology is confirmed properly first.

How treatment is carried out

Avelumab is administered intravenously once every two weeks. Premedication — an antihistamine and paracetamol — is given before every session. This is standard, not optional. Infusion-related reactions occur more frequently with this drug than with most other checkpoint inhibitors, and premedication meaningfully reduces that risk.

Monitoring during treatment includes:

• blood count and full chemistry panel;

• liver function tests;

• thyroid hormones at set intervals;

• kidney function;

• imaging to track treatment response;

• close observation during the first several sessions.

I say the same thing to every patient before the first infusion: if anything changes during the drip — warmth, chills, difficulty breathing — say so immediately. To whoever is in the room. Not at the end of the session. Not at home. Right then.

Possible side effects

Side effects that may appear:

• infusion reactions — chills, fever, flushing;

• fatigue;

• skin rash or itching;

• diarrhoea;

• thyroid dysfunction — either direction;

• lung inflammation;

• elevated liver enzymes;

• joint discomfort;

• nausea;

• rarely — cardiac or neurological involvement.

Infusion reactions are what makes avelumab distinct. Most are mild. Occasionally more significant. That is exactly why premedication is given before every session — not just after a reaction has already occurred. The first few infusions are when the risk is highest. After that, reactions typically become less frequent.

When to contact a doctor urgently

Do not wait if any of the following develop:

• any symptom during the infusion — speak up immediately to the nursing staff;

• breathlessness or chest tightness after leaving the clinic;

• severe or worsening diarrhoea;

• blood in the stool;

• yellowing of the skin or eyes;

• fever on a day without an infusion;

• growing confusion or weakness;

• a sudden significant drop in how you feel.

With immune-related side effects, acting early changes what is possible. Waiting rarely helps.

Why avelumab is not right for everyone

What affects whether this drug is appropriate:

• a cancer type outside the two approved indications;

• bladder cancer that progressed on platinum chemotherapy — maintenance does not apply;

• active severe autoimmune disease;

• prior organ transplant;

• overall health that makes tolerating treatment difficult;

• history of severe infusion reactions.

The chemotherapy response question in bladder cancer is not a formality. The maintenance approach only makes clinical sense for patients whose disease responded or held stable. Without that, there is no foundation for this strategy.

Can avelumab be combined with other treatments

In the approved indications, avelumab is used as monotherapy. Combinations are being studied but are not part of standard practice at this time.

In Merkel cell carcinoma, radiation sometimes plays a role in the overall treatment picture. Whether it runs alongside avelumab or is sequenced around it depends on the individual clinical situation.

What ‘no quick response’ means

In Merkel cell carcinoma, immune responses develop over time. Early scans can look stable or ambiguous before meaningful improvement becomes visible. Some patients show delayed responses — stable early imaging that later converts to a clear result. This is not failure.

In bladder cancer maintenance, the goal is not tumour shrinkage. It is keeping things stable. I explain this clearly before treatment starts — so that unchanged scans feel like success, not stagnation.

Oncology consultation for avelumab (Bavencio) in Israel

At Tel Aviv Medical Clinic in Israel, consultations are available on the use of avelumab (Bavencio) for Merkel cell carcinoma and bladder cancer. Merkel cell carcinoma is rare enough that specialist input is genuinely valuable — both to confirm the diagnosis is correct and to discuss what the treatment options actually are. Oncologists at the clinic follow ESMO and NCCN guidelines and are experienced in both indications.

In Tel Aviv Medical Clinic, you can discuss:

• whether the pathological diagnosis has been properly confirmed;

• whether avelumab fits your current clinical situation;

• maintenance therapy in bladder cancer — who qualifies and who does not;

• a second opinion on a proposed treatment plan;

• what options remain if avelumab has stopped being effective;

• how treatment in Israel compares to what is available internationally.

We do not prescribe remotely. We help patients understand their options — and what questions are worth raising at the next appointment.

Frequently Asked Questions — Dr. Stefanskoy

1. What is Merkel cell carcinoma and why is avelumab used for it?

Merkel cell carcinoma is a rare skin cancer arising from specific cells involved in sensory function. It tends to spread to lymph nodes and other sites earlier than most other skin cancers. Before immunotherapy became available in this space, systemic treatment options were limited and results did not last.

Clinical data showed avelumab produced responses that held up considerably longer than prior chemotherapy approaches had achieved. That changed the standard approach to advanced disease in this cancer. Later data confirmed the benefit even in patients who had not previously received systemic treatment.

2. What does maintenance therapy mean in bladder cancer?

It means the cancer responded to platinum-based chemotherapy — or at least held stable — and the goal now is to maintain that position for as long as possible. Avelumab is not treating active growing disease. It is preventing the next episode of progression.

Trial data showed that patients who received avelumab after responding to chemotherapy had longer survival than those who moved to observation. But the eligibility is strict. Patients whose cancer grew during chemotherapy are not candidates for this approach. That distinction is central to the decision.

3. Why do infusion reactions happen more often with avelumab?

The precise reason is not fully established. The drug’s molecular characteristics — including how it interacts with natural killer cells — are thought to contribute. What clinical experience showed clearly is that reactions during infusion occur more often with avelumab than with comparable checkpoint inhibitors.

That is the reason premedication is given before every session — not only after a reaction has occurred. And patients need to know: any symptom during the infusion means speaking up immediately. To the nursing staff. Not once the session is over.

4. Does virus status in Merkel cell carcinoma affect treatment?

No — not for eligibility. Avelumab is used in both virus-positive and virus-negative Merkel cell carcinoma. Early observations suggested slightly different response patterns between the groups, but both show benefit from treatment.

What determines eligibility is the confirmed histological diagnosis, the extent of disease and the treatment history. Virus status is documented but does not open or close any treatment pathways.

5. How long does treatment continue?

In Merkel cell carcinoma — until the disease progresses again or side effects make continuing impractical. For patients with deep or complete responses, when to stop is an open clinical question. There is no fixed stopping point in the standard protocol.

In bladder cancer maintenance — the same principle applies. Treatment continues as long as the disease remains controlled and the patient tolerates it. The clinical course determines the duration, not a calendar.

6. Are there alternatives if avelumab is not appropriate?

In Merkel cell carcinoma, another immune checkpoint drug has shown activity and is used in some settings, though it has less dedicated evidence specifically in this cancer. Chemotherapy remains available when immunotherapy is not suitable.

In bladder cancer, avelumab is currently the only agent in this specific post-chemotherapy maintenance role. For patients who are not eligible or who progress, next steps depend on what treatment has already been used.

7. What happens when avelumab stops working?

In Merkel cell carcinoma — chemotherapy is one path. Clinical trials are another. Given how rare this cancer is, I raise the question of trial access early — not as a last resort after standard options run out.

In bladder cancer — progression on maintenance moves treatment to the next available option, based on prior treatment history and the patient’s current condition. There is no single answer. It is worked out individually each time.

Important information

Avelumab (Bavencio) is considered only after a full clinical assessment — diagnosis, disease stage, treatment history, organ function and overall patient condition.

Do not start, stop or change treatment without consulting your treating physician.

For a consultation in Israel:

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