Peritoneal Surface Malignancy
Peritoneal surface malignancy covers disease involving the peritoneal lining, whether arising there primarily or spreading from another site. Management is concentrated at specialist centres because the surgical approach is highly specialised.
Disease categories
Major disease categories
- Primary peritoneal carcinoma
- Peritoneal mesothelioma
- Pseudomyxoma peritonei
- Peritoneal metastases from colorectal, gastric, ovarian or appendiceal primaries
Molecular
Molecular considerations
Molecular findings follow the tumour of origin. Primary peritoneal carcinoma is managed as high-grade serous disease, with BRCA and homologous recombination status relevant. Peritoneal mesothelioma carries BAP1 and NF2 alterations.
Markers commonly discussed in peritoneal surface malignancy
- BRCA1/2 and HRD (serous)
- BAP1 (mesothelioma)
- KRAS / GNAS (mucinous)
- MMR / MSI
- CEA
- CA 125
Not exhaustive, and not every marker is assessed in every patient. Which of these is relevant depends on the individual case and should be discussed with the treating team.
Testing
Genomic testing considerations
Profiling directed by the tumour of origin, which is the first question to settle.
Germline
Germline considerations
Germline testing is discussed where the disease is serous in type, given the overlap with ovarian cancer.
Molecular monitoring
ctDNA and liquid biopsy considerations
Peritoneal disease is often a low shedder into plasma, which limits ctDNA interpretation.
Single-cell & computation
Single-cell and algorithmic approaches
Where the primary site is unresolved or the entity is rare, computational methods carry proportionally more of the reasoning. Single-cell analysis characterises cellular composition where histology is ambiguous. Algorithm work includes tissue-of-origin classification from expression and methylation data, cross-disease evidence synthesis from small series, and retrieval methods built for literatures too small for conventional meta-analysis.
Decisions
Treatment decision questions
Questions worth raising with a treating team when a decision is being made:
- Has the tumour of origin been established?
- Is the peritoneal disease burden documented?
- Has assessment at a peritoneal surface malignancy centre been considered?
Resistance
Resistance and recurrence questions
- Has the histology been reviewed where behaviour is atypical?
Trials
Clinical trial considerations
Trials are concentrated at specialist centres; origin determines the relevant set.
When a precision oncology review may help
A review is most useful where the standard pathway has been exhausted or where the picture is more complicated than a protocol accounts for — rare presentations, treatment resistance, complex or apparently contradictory molecular findings, or a decision between several defensible options.
The output is a structured analysis and a set of questions for the treating team. It is not treatment, and it does not replace the treating oncologist.