Anal Cancer
Anal cancer is strongly associated with persistent human papillomavirus infection and is managed quite differently from colorectal cancer despite their anatomical proximity — a distinction that matters from the first consultation onward.
Disease categories
Major disease categories
- Anal squamous cell carcinoma
- Anal margin tumours
- Anal adenocarcinoma
- Anal melanoma
Molecular
Molecular considerations
HPV association is characteristic. PIK3CA alterations are described, and PD-L1 expression is assessed in advanced disease. Immunosuppression, including HIV status, is relevant to the clinical picture.
Markers commonly discussed in anal cancer
- HPV / p16
- PD-L1
- PIK3CA
- TMB
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
Molecular profiling is discussed in recurrent and metastatic disease rather than routinely at diagnosis.
Germline
Germline considerations
Not routinely indicated; considered where the presentation is unusual.
Molecular monitoring
ctDNA and liquid biopsy considerations
HPV circulating DNA is an area of research interest for surveillance in this disease.
Single-cell & computation
Single-cell and algorithmic approaches
In gastrointestinal and hepatobiliary disease, single-cell sequencing is used chiefly to characterise the tumour microenvironment and to resolve clonal structure in tumours that are heterogeneous between regions. Single-cell DNA analysis helps establish whether a RAS or driver alteration is clonal or subclonal, which bears directly on how much weight it should carry. Algorithm work here includes molecular residual disease detection from serial samples, mismatch repair classification from sequencing data, and pipelines that reconcile findings across multiple biopsy sites.
Decisions
Treatment decision questions
Questions worth raising with a treating team when a decision is being made:
- Has HPV status been documented?
- Is the histological subtype clear, particularly where melanoma or adenocarcinoma is possible?
- Has immunosuppression status been recorded?
Resistance
Resistance and recurrence questions
- Has the disease been re-characterised at recurrence?
- Has a second primary been considered?
Trials
Clinical trial considerations
HPV status and PD-L1 expression shape the relevant trial 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.