If you had to have a mesothelioma, is peritoneal mesothelioma the one you would choose? | Dr Dilanka De Silva

A 56-year-old woman. Extremely fit. Regular exercise. No recognised occupational asbestos exposure.

After returning from a trip to Europe, she began noticing abdominal swelling and bloating. During a training session, even lying flat to perform an abdominal exercise suddenly felt unusually difficult.

One investigation led to another.

Eventually, she was diagnosed with a very rare cancer: malignant peritoneal mesothelioma.

When people hear the word mesothelioma, they often immediately think of asbestos and cancer around the lungs.

But this cancer began in the peritoneum—the lining of the abdomen.

Asbestos remains an important risk factor for mesothelioma, but not every patient with peritoneal mesothelioma has a recognised exposure history.

The question we then faced was:

“Could surgery and HIPEC give me years of disease control—or is my cancer currently too extensive for such a major operation?”

Peritoneal mesothelioma treatment depends heavily on the answer to that question.

Some personal details have been adjusted to protect patient confidentiality.

Who is this article for?

This article may be helpful if you have:

• peritoneal mesothelioma;
• epithelioid mesothelioma involving the abdomen;
• been referred to discuss cytoreductive surgery and HIPEC;
• been told your disease is currently too extensive for surgery; or
• questions about chemotherapy versus immunotherapy.

The diamond answer

For carefully selected patients with peritoneal mesothelioma, cytoreductive surgery and HIPEC can be associated with survival measured in years.

But the most important question is not simply:

“Can I have HIPEC?”

It is:

“Can an experienced surgeon safely remove all or almost all visible cancer?”

If that appears achievable, major surgery—often combined with treatment inside the abdomen such as HIPEC—may form an important part of the treatment plan.

If the cancer is too extensive to remove safely, treatment throughout the body, such as chemotherapy or immunotherapy, may be more appropriate first. Surgery can sometimes be reconsidered later if the cancer responds, but this cannot be guaranteed.

Current expert guidance emphasises specialist multidisciplinary assessment because there is no single treatment sequence that is right for every patient.

What exactly are cytoreductive surgery and HIPEC?

They are two different parts of treatment.

Cytoreductive surgery means removing as much visible cancer as possible from inside the abdomen.

HIPEC, or hyperthermic intraperitoneal chemotherapy, involves circulating heated chemotherapy through the abdomen during the operation.

The aim is to treat microscopic cancer cells that may remain after the visible disease has been removed.

The important point is:

HIPEC is unlikely to compensate for an operation where a large amount of visible cancer has to be left behind.

That is why the possibility of complete or near-complete cancer removal is so important when deciding whether surgery is worthwhile.

Who is most likely to benefit?

Patients considered for major surgery generally need to be fit enough for a complex operation and have disease that a specialist team believes can be removed to a meaningful extent.

Factors that may favour surgery include:

• disease mainly confined to the abdomen;
• the epithelioid type, which generally tends to behave less aggressively than the biphasic and sarcomatoid types;
• limited involvement of the small bowel and its supporting tissues; and
• a realistic possibility of removing all or almost all visible cancer.

The amount of cancer matters, but where it is located can matter just as much.

This is why the decision should be made by a team experienced in peritoneal cancers rather than from a scan report alone.

What does the long-term evidence actually show?

This is where peritoneal mesothelioma can surprise people.

In the largest international surgical series, 405 patients with malignant peritoneal mesothelioma were treated using cytoreductive surgery and HIPEC at specialist centres.

Median survival was 53 months—about 4½ years.

At three years, approximately 60 in every 100 patients were alive.

At five years, approximately 47 in every 100 were alive.

Those numbers are encouraging, but they need an important qualification:

These were carefully selected patients who were suitable for major surgery. They are not the expected outcomes for every person diagnosed with peritoneal mesothelioma.

Another study involving 211 surgical patients reported:

• approximately 41 in every 100 alive at five years; and
• approximately 26 in every 100 alive at ten years.

So yes—some patients can live well beyond five years.

But we should not turn these retrospective surgical results into a promise for an individual patient.

Why does the amount of cancer removed matter so much?

Both major surgical series found that patients did better when surgeons were able to achieve complete or near-complete removal of visible disease.

That is why being physically fit is not enough.

A patient may be healthy enough to tolerate the operation, but the distribution of the cancer may still make meaningful surgery impossible.

I would not recommend a major operation simply because it can technically be performed. The surgical team needs to believe that removing almost all visible disease is realistically achievable.

What did I tell my patient?

My patient was exceptionally fit.

However, after discussion with an experienced surgeon, her current volume and distribution of disease were considered too extensive for meaningful cytoreductive surgery.

That does not mean there are no treatment options.

For her, I would favour carboplatin and pemetrexed, assess how the cancer responds and then reconsider the surgical question with the multidisciplinary team.

I cannot promise that chemotherapy will make an inoperable cancer operable.

But reassessing after systemic treatment is reasonable when there has been meaningful disease control.

What is the evidence for chemotherapy?

Because peritoneal mesothelioma is rare, the chemotherapy evidence is much smaller than for common cancers.

In an expanded-access study of 98 patients with peritoneal mesothelioma, approximately 1 in 4 evaluable patients had measurable tumour shrinkage, while around 7 in 10 achieved either tumour shrinkage or stable disease with pemetrexed-based treatment.

A later study of 109 patients also showed activity with pemetrexed combined with either cisplatin or carboplatin. Response rates differed between treatment groups, including approximately 24 in every 100 patients receiving carboplatin–pemetrexed.

These were not modern randomised trials, so I would use these figures to show that chemotherapy can work—not to predict exactly how one patient will respond.

What about immunotherapy?

This is an evolving area.

Nivolumab plus ipilimumab is well established in pleural mesothelioma, but the original large randomised trial was conducted in pleural rather than peritoneal disease.

More recent peritoneal-mesothelioma consensus guidance nevertheless includes both platinum–pemetrexed-based chemotherapy and nivolumab plus ipilimumab as possible first-line approaches for epithelioid disease. Clinical-trial participation should also be considered whenever possible.

Peritoneal-specific immunotherapy studies are encouraging but small.

Atezolizumab plus bevacizumab

A phase II study included only 20 patients whose cancer had already progressed after, or could not tolerate, platinum–pemetrexed chemotherapy.

• 8 of 20 patients—40%—had measurable tumour shrinkage.
• Median time before the cancer progressed was approximately 17.6 months.
• At one year, approximately 61 in 100 remained progression-free.
• Approximately 85 in 100 were alive at one year.

Those are encouraging results, but a 20-patient study cannot prove that this treatment is better than chemotherapy as first treatment.

Pembrolizumab

A separate retrospective study included 24 patients.

Among those who could be evaluated for response, approximately 21% had partial tumour shrinkage. Median progression-free survival was 4.9 months, and median overall survival from starting pembrolizumab was 20.9 months.

Again, this tells us that immunotherapy can be active. It does not tell us that it is automatically the best first treatment for every patient.

What does BAP1 loss mean?

My patient’s tumour showed loss of BAP1. BAP1 is a protein that normally helps prevent cells from growing abnormally. When BAP1 is lost in a mesothelial tumour, it can help pathologists support a diagnosis of malignant mesothelioma.

Pathologists may also use tests such as MTAP and CDKN2A when trying to distinguish malignant mesothelioma from other mesothelial conditions.

However, I would not tell a patient that BAP1 loss guarantees a better prognosis or predicts a particular treatment response. Studies have produced differing results, so it is not a reliable stand-alone survival marker.

There is another question:

“Could the BAP1 finding be inherited?”

Usually, loss of BAP1 within the tumour does not by itself prove an inherited BAP1 syndrome.

But international guidance says germline BAP1 testing may reasonably be considered in someone who develops mesothelioma before age 60 without recognised asbestos exposure. That makes genetic assessment particularly relevant in a patient like this.

What are the important risks of surgery and HIPEC?

This is major treatment.

In the large 2009 international surgical series:

• approximately 31 in every 100 patients experienced a serious grade 3 or 4 complication; and
• approximately 2 in every 100 died around the time of surgery.

These are historical multi-centre figures rather than an estimate of what would happen at a particular modern Australian centre.

The risks for an individual patient depend on the extent of surgery, their health, the centre’s experience and many other factors.

That is why I would ask the treating centre about its own complication and mortality rates, rather than relying only on historical studies.

The Australian perspective

In Australia, cytoreductive surgery for peritoneal mesothelioma is highly specialised and performed by a relatively small number of surgeons.

Cancer Council Australia similarly recommends specialist surgical assessment when peritonectomy or HIPEC is being considered. Chemotherapy, immunotherapy and surgery may all have roles depending on the individual situation.

For a rare cancer like this, I would also consider:

• specialist pathology review;
• discussion in an experienced multidisciplinary team;
• appropriate tumour and germline genetic testing; and
• clinical trials where available.

What would I usually consider?

For an individual patient, I would want clear answers to a few questions:

1. Is the cancer mainly confined to the abdomen?
2. Is it epithelioid, biphasic or sarcomatoid?
3. Can almost all visible cancer realistically be removed?
4. How extensively is the small bowel involved?
5. Should treatment begin with surgery or with systemic treatment?
6. If chemotherapy or immunotherapy is given first, should surgery be reconsidered after response?
7. Does the pathology—including BAP1—need specialist review?
8. Should germline genetic testing be considered?
9. Is there a suitable clinical trial?

The goal is not simply to choose the most aggressive treatment.

It is to choose the treatment sequence most likely to provide meaningful and durable disease control for that particular patient.

What surprised me?

The word mesothelioma often creates the assumption that survival must always be short.

That is not true for every patient with peritoneal mesothelioma.

Among highly selected patients who underwent major cytoreductive treatment, one international series reported a median survival of approximately 4½ years, with 47 in 100 alive at five years. Another series reported approximately 26 in 100 alive at ten years.

These are not promises.

But they explain why peritoneal mesothelioma deserves its own careful treatment discussion rather than simply being treated as pleural mesothelioma in a different location.

Key takeaways

• Peritoneal mesothelioma is different from the more familiar pleural form, and some patients have no recognised asbestos exposure.
• For carefully selected patients, cytoreductive surgery with HIPEC has been associated with survival measured in years—but the evidence largely comes from selected surgical series.
• If surgery is not currently feasible, chemotherapy or immunotherapy may be considered, with later surgical reassessment in selected patients.
• BAP1 loss can help support the diagnosis but does not automatically predict prognosis or mean the condition is inherited.

Key evidence

1. Brown LM, Wilkins SG, Bansal VV, et al. Consensus guideline for the management of peritoneal mesothelioma. Cancer. 2025;131(13):e35868. doi:10.1002/cncr.35868
2. Yan TD, Deraco M, Baratti D, et al. Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for malignant peritoneal mesothelioma: multi-institutional experience. J Clin Oncol. 2009;27(36):6237-6242. doi:10.1200/JCO.2009.23.9640
3. Alexander HR Jr, Bartlett DL, Pingpank JF, et al. Treatment factors associated with long-term survival after cytoreductive surgery and regional chemotherapy for patients with malignant peritoneal mesothelioma. Surgery. 2013;153(6):779-786. doi:10.1016/j.surg.2013.01.001
4. Carteni G, Manegold C, Garcia GM, et al. Malignant peritoneal mesothelioma-results from the International Expanded Access Program using pemetrexed alone or in combination with a platinum agent. Lung Cancer. 2009;64(2):211-218. doi:10.1016/j.lungcan.2008.08.013
5. Raghav K, Liu S, Overman MJ, et al. Efficacy, safety, and biomarker analysis of combined PD-L1 (atezolizumab) and VEGF (bevacizumab) blockade in advanced malignant peritoneal mesothelioma. Cancer Discov. 2021;11(11):2738-2747. doi:10.1158/2159-8290.CD-21-0331
6. Marmarelis ME, Wang X, Roshkovan L, et al. Clinical outcomes associated with pembrolizumab monotherapy among adults with diffuse malignant peritoneal mesothelioma. JAMA Netw Open. 2023;6(3):e232526. doi:10.1001/jamanetworkopen.2023.2526
7. Husain AN, Chapel DB, Attanoos R, et al. Guidelines for pathologic diagnosis of mesothelioma: 2023 update of the consensus statement from the International Mesothelioma Interest Group. Arch Pathol Lab Med. 2024;148(11):1251-1271. doi:10.5858/arpa.2023-0304-RA
8. Lalloo F, Kulkarni A, Chau C, et al. Clinical practice guidelines for the diagnosis and surveillance of BAP1 tumour predisposition syndrome. Eur J Hum Genet. 2023;31(11):1261-1269. doi:10.1038/s41431-023-01448-z

Frequently asked questions (FAQs)

1. Should everyone with peritoneal mesothelioma have HIPEC?

No. The key question is whether an experienced surgical team believes all or almost all visible disease can be removed safely.

2. Can chemotherapy make an inoperable cancer operable?

Sometimes the disease may shrink enough for surgery to be reconsidered, but this is not predictable and should not be promised.

3. Is immunotherapy better than chemotherapy?

We do not yet have a definitive peritoneal-specific randomised trial answering that question. Both may be reasonable options depending on histology, disease extent, previous treatment and the individual patient.

4. Does BAP1 loss mean I inherited the cancer?

No. BAP1 can be lost only within the tumour. A separate blood or saliva test is required to determine whether there is an inherited BAP1 variant.

5. Can patients live longer than five years?

Yes. In carefully selected surgical series, approximately 41%–47% were alive at five years, with one large series reporting approximately 26% alive at ten years. Those numbers mainly apply to patients selected for major cytoreductive treatment.

About Dr Dilanka De Silva

Dr Dilanka De Silva is a Melbourne-based Medical Oncologist and Cancer Genetics Physician with experience in precision oncology, rare cancers, hereditary cancer assessment and complex cancer second opinions.

He completed fellowship training at Memorial Sloan Kettering Cancer Center in New York and reviews Australian and international patients, including patients from Sri Lanka, the Maldives, Indonesia and the Philippines.

Dr Dilanka De Silva
MBBS, MRCP(UK), MRCP(UK SCE Oncology), FRACP, PhD
Medical Oncologist & Cancer Genetics Physician
Memorial Sloan Kettering Cancer Center Fellow (New York, USA)