From BBC News:
Every time a cell divides, it has to remember which of its genes are switched on or off at the time. If that memory is impaired, this can disrupt the proper development of cells and trigger cancer. Scientists at Cancer Research UK and Cambridge’s Babraham Institute have shown certain enzymes can alter this genetic memory. Evidence of this interference was present in a large proportion of tumours – strongly implicating the enzymes in the development of cancer. Retaining the memory of which genes are switched on and which are switched off when a cell divides is called epigenetics. Often genes are switched off by a change to the structure of its component DNA – a process known as methylation. The researchers discovered that AID, an enzyme involved in the formation of the immune system, can also alter methylation in DNA. This could leave cells with inaccurate memories – and lead to cancer.