Primary peritoneal cancer
Primary peritoneal cancer is a malignancy arising from the peritoneal lining itself, without an identifiable tumour in the ovaries or anywhere else. It is uncommon, it occurs almost exclusively in women, and it looks and behaves so much like advanced ovarian cancer that it is now classified and treated as part of the same disease group. Understanding why that is — and why it can occur in women who have had both ovaries removed — is the key to the whole condition.
How it develops
The explanation lies in embryology. During development, the coelomic epithelium lining the body cavity gives rise both to the peritoneum and to the germinal epithelium covering the ovary, and to the Müllerian ducts from which the fallopian tubes, uterus and upper vagina form. Peritoneum and ovarian surface therefore share a common origin and retain a shared capacity for malignant change — what is sometimes described as the "secondary Müllerian system".
This explains the two defining features of the condition: the peritoneum can give rise to a tumour histologically identical to ovarian cancer, and it can do so in a woman whose ovaries have been removed — including women who underwent risk-reducing oophorectomy for a BRCA mutation, in whom a small residual risk of primary peritoneal cancer persists.
Current understanding has shifted further. Molecular and pathological work over the last two decades indicates that many tumours previously labelled as primary peritoneal or ovarian high-grade serous carcinoma in fact originate in the fimbrial end of the fallopian tube, from a precursor lesion called serous tubal intraepithelial carcinoma (STIC). Cells shed from the tube seed the ovary and peritoneum, producing widespread disease with no obvious primary. This is why the whole group is now managed as a single entity — tubo-ovarian and peritoneal high-grade serous carcinoma — and why removal of the fallopian tubes has become an important preventive measure.
The characteristic molecular events are near-universal TP53 mutation and, in a substantial proportion, defective homologous recombination repair through BRCA1 or BRCA2 mutation or other mechanisms. This last point has direct therapeutic consequence: tumours that cannot repair DNA by homologous recombination are exquisitely sensitive to PARP inhibitors, which block the alternative repair pathway and kill the cell — the principle of synthetic lethality.
Diagnostic criteria
Formally, primary peritoneal cancer is diagnosed when the ovaries are normal or only minimally involved on their surface, the extent of disease in the peritoneum exceeds that on the ovarian surface, and the histology is serous. In practice, careful examination of the fallopian tubes frequently identifies the true origin.
Symptoms
Insidious and non-specific, which is why the disease is usually advanced at diagnosis.
- Abdominal distension and bloating — often the earliest symptom, and frequently attributed to irritable bowel syndrome or the menopause for months
- abdominal or pelvic pain
- early satiety and loss of appetite
- change in bowel or urinary habit — urinary frequency and urgency are common
- weight loss with a distended abdomen
- fatigue
- a pelvic or abdominal mass
- breathlessness from ascites or pleural effusion
Persistent bloating, early satiety, pelvic pain and urinary urgency in a woman over fifty, occurring on most days for more than a few weeks, should prompt investigation with CA 125 and ultrasound rather than symptomatic treatment. This symptom cluster is the basis of ovarian cancer awareness campaigns, and it applies identically here.
How the diagnosis is made
- CA 125 — usually markedly raised. It is not specific — endometriosis, fibroids, infection, liver disease and even menstruation raise it — but in a postmenopausal woman with these symptoms it is informative, and it is invaluable for monitoring treatment.
- Pelvic and abdominal ultrasound — assessing the ovaries, which are characteristically normal or minimally enlarged, and demonstrating ascites and omental disease.
- CT of chest, abdomen and pelvis — defining extent, ascites, omental caking, peritoneal nodules and pleural disease.
- Histology — from image-guided biopsy of omental or peritoneal disease, or at laparoscopy. Immunohistochemistry (PAX8, WT1, p53, CK7) confirms the Müllerian origin and distinguishes it from mesothelioma and from metastatic gastrointestinal cancer, which is the crucial differential.
- Laparoscopy — for tissue diagnosis and, importantly, to assess whether complete surgical removal is achievable.
- Genetic testing — germline and tumour BRCA testing and homologous recombination deficiency status should be performed in all patients, since they determine treatment and have major implications for female relatives.
Treatment
Treatment follows the protocols for advanced high-grade serous ovarian cancer and is led by a gynaecological oncology multidisciplinary team.
Surgery
The objective is complete cytoreduction — no visible residual disease. This is the single strongest modifiable determinant of survival, and the difference between complete cytoreduction and leaving even small-volume residual disease is substantial.
The operation typically includes total hysterectomy, bilateral salpingo-oophorectomy, omentectomy, peritoneal stripping, and resection of involved bowel, spleen or diaphragmatic peritoneum as required. It is extensive surgery and is best performed by surgeons who undertake it regularly, with general surgical and hepatobiliary support available.
- Primary debulking surgery — surgery first, then chemotherapy, where complete removal is judged achievable at the outset.
- Neoadjuvant chemotherapy with interval debulking — chemotherapy first to shrink the disease, then surgery, then further chemotherapy. Preferred where the disease is too extensive for complete primary removal, or where the patient is not fit for major surgery initially. Outcomes are comparable with less morbidity in that group.
Chemotherapy
Platinum-based chemotherapy with a taxane — carboplatin and paclitaxel — is the standard. These tumours are characteristically chemosensitive, which is an important and hopeful point: response rates are high even with extensive disease.
Maintenance treatment
This is where outcomes have improved most in recent years.
- PARP inhibitors — olaparib, niraparib and others, given as maintenance after response to chemotherapy. The benefit is very substantial in BRCA-mutated and homologous recombination-deficient tumours, and meaningful more broadly.
- Bevacizumab — an antiangiogenic antibody, used with chemotherapy and as maintenance.
HIPEC
Heated intraperitoneal chemotherapy given at the time of interval debulking surgery has shown a survival benefit in a randomised trial in this setting, and is used in some centres. Its place remains under discussion, and practice varies.
Recurrent disease
Treatment depends on the interval since platinum treatment. Platinum-sensitive recurrence is treated with further platinum-based chemotherapy, with secondary cytoreductive surgery in selected patients with limited, resectable recurrence and good performance status. Platinum-resistant disease is treated with single-agent chemotherapy, antiangiogenic agents and clinical trials.
Recovery
Extensive cytoreductive surgery involves a hospital stay of one to two weeks, often with critical care, and a recovery of two to three months. Chemotherapy is usually given as six cycles over about eighteen weeks, with the expected effects on blood counts, nerves and hair. Surgical menopause follows oophorectomy in premenopausal women and should be discussed, including the question of hormone replacement, which is not automatically contraindicated.
Follow-up and family
Clinical review, CA 125 and imaging as indicated. Genetic counselling and testing of relatives is a central part of care: identifying a BRCA mutation allows female relatives to consider surveillance, risk-reducing salpingo-oophorectomy and breast screening, and has implications for male relatives too. This is one of the situations where a diagnosis in one person materially alters the future health of a whole family.
When to seek an opinion
Persistent bloating, early satiety, pelvic or abdominal pain, or urinary urgency occurring on most days for more than three weeks, particularly in a woman over fifty, should be investigated. A woman who has had her ovaries removed can still develop this condition, and such symptoms should not be dismissed on that basis.
Common questions
How can I have ovarian-type cancer when my ovaries have been removed?
Because the lining of the abdomen and the surface of the ovary develop from the same tissue in the embryo and retain the same capacity to become cancerous. It is also now understood that many of these cancers actually begin in the fallopian tube and shed cells into the abdomen. So the disease can occur without ovaries being present.
Is this the same as ovarian cancer?
Effectively yes. It is the same type of cancer under the microscope, it behaves the same way, and it is treated with the same surgery and chemotherapy. It is now grouped with ovarian and fallopian tube cancer as a single disease, which is why you may hear all three terms used.
Why was my CA 125 normal (or raised for another reason)?
CA 125 is a useful test but not a perfect one. It can be raised by endometriosis, fibroids, infection, liver disease and other conditions, and it is occasionally normal despite cancer being present. It is most useful in combination with a scan, and it is particularly valuable for monitoring how treatment is working once a diagnosis is made.
Should I have surgery first or chemotherapy first?
It depends on whether all visible disease can realistically be removed at the outset, and on your fitness. Where it can, surgery first is preferred. Where the disease is very extensive, chemotherapy first shrinks it, making complete removal more achievable and the operation safer, with comparable results. This is an individual decision made by the team after reviewing your scans and often a laparoscopy.
What are PARP inhibitors?
Tablets that block one of the cell's DNA repair pathways. Cancer cells that already have a fault in the other main repair pathway — which is the case with BRCA mutations and some related faults — cannot then repair their DNA at all and die, while normal cells survive. They are given after chemotherapy to keep the disease under control, and they have made a substantial difference to outcomes.
Should my daughters be tested?
If you carry a BRCA mutation or a related inherited fault, yes — this is an important part of your care. Testing allows relatives who carry it to consider preventive measures, including surgery to remove the tubes and ovaries and additional breast screening. It affects male relatives too. Genetic counselling is offered as part of this.
Is it treatable?
Yes. These tumours respond well to chemotherapy even when extensive, which is one of the more hopeful aspects of the disease. Removing all visible disease surgically and following with chemotherapy and maintenance tablets gives many patients long periods of good health, and some are cured. The disease can recur and is then often treatable again.
Why were my symptoms put down to irritable bowel or the menopause?
Because the early symptoms — bloating, feeling full quickly, discomfort, needing to pass urine more often — are common and usually caused by something benign. What distinguishes them here is that they are persistent, occur on most days, and are new. Any woman with that pattern for more than three weeks should have a CA 125 and a scan.
Related conditions
Other conditions of the peritoneal disease covered on this site:
- Peritoneal metastases
- Pseudomyxoma peritonei
- Peritoneal mesothelioma
- Peritonitis
- Intra-abdominal abscess
- Adhesions and adhesive bowel obstruction
This page provides general information and does not replace an individual medical consultation. Primary peritoneal cancer is managed by a gynaecological oncology multidisciplinary team.