The only randomised controlled trial examining the effect
of aspirin in primary prevention of colon cancer did not show
any benefit after five years of aspirin use. A recent prospective
cohort study suggested, however, that five years may be
insufficient to show any benefit and that 10-20 years is needed
to show an effect.

The predominant side effect from using non-steroidal
anti-inflammatory drugs is the increased incidence of
gastrointestinal bleeds. On the current evidence, the mortality
risk from such bleeding would be outweighed by the reduction
in mortality from colon cancer. To maximise the benefit to risk
ratio, however, targeting individuals at high risk of colon cancer
may prove more fruitful.

Non-steroidal anti-inflammatory drugs could be used as
secondary prevention after surgical resection of colonic
tumours, but this approach has yet to be tested in a large
randomised controlled trial.

Many cancers can be destroyed by a tumour specific, cell
mediated immune response, usually by CD8 (cytotoxic)
lymphocytes. However, colorectal tumours are poorly
immunogenic and may evade immune destruction by various
mechanisms, such as tumour “tolerance.” To overcome these
problems, several immunostimulatory approaches have been
advocated to augment the innate immune response against
tumours.

Vaccination with autologous tumour cells
This approach uses cells derived from the patient’s tumour to
elicit a cell mediated immune response against the tumour. To
increase the efficacy of this response, tumour cells are
coadministered with an immunomodulatory adjuvant, such as
BCG. This approach has been tested in three randomised,
controlled trials in an adjuvant setting in colorectal cancer, after
resection of the tumour. No serious side effects were
encountered in any of the studies.