It is impossible to predict with certainty an individual’s response to treatment and therefore survival. However, factors associated with a poor prognosis include a positive resection margin (i.e. tumour involved at the resection margin), large cancers (>5cm), spread of the cancer into the muscle of the pelvic floor (levator ani muscle), and spread of cancer to lymph nodes.
These form the basis for the AJCC staging of anal cancer which is calculated as follows:
| T stage | Overall stage |
| T1 (< 2cm) | I |
| T2 (2cm-5cm) | IIa |
| T3 (>5cm) | IIb |
| T4 (vaginal invasion or spread to anal lymph nodes) | IIIa |
| T4 (invasion of other structures or spread to groin lymph nodes) | IIIB |
| M1 (distant metastases) | IV |
Prognostic factors
Most patients treated with chemo radiotherapy have an excellent prognosis. The most important and reliable prognostic factors are the size of the cancer (i.e. T stage) and the presence or absence of spread to lymph nodes (i.e. N stage). Distant spread to other organs (i.e. M stage) is associated with the poorest outcome.
5 Year survival based on the stage was obtained from a cohort of 19,995 patients with anal cancer in the US National cancer database, between 1985-2000 period.
The 5-year survival based on T and N stage would be:
| T1 (<2cm) | 90% |
| T2 (2-5cm) | 85% |
| T3 (>5cm) | 60% |
| T4 (invading other structures) | 45% |
| N0 (no nodal spread) | 75% |
| N+ (nodal spread) | 55% |
| M+ (distant metastases) | 20% |
5-year overall survival based on the AJCC staging was:
| Stage I | 70% |
| Stage II | 60% |
| Stage III | 40% |
| Stage IV | 20% |
