Canadian scientists have used highly-advanced new DNA sequencing technology to identify a single tiny genetic mutation that causes nearly all incidences of a rare and deadly type of ovarian cancer. The discovery may lead to new ways to diagnose and treat the cancer, and also raises the possibility that the new approach may be the key to advancing our understanding of the genetic causes of other rare cancers.

The research team, from the Ovarian Cancer Research (OvCaRe) Program at British Columbia (BC) Cancer Agency and Vancouver Coastal Health Research Institute, used so-called 'next generation' sequencing technology to decode the entire genetic sequence - which contains over 20,000 genes - of cells from four granulosa cell tumours. They found that cells from each tumour had the same mutation, which altered just one letter out of the three billion that make up the human genetic code. Dr Marco Marra, of the BC Cancer Agency said that 'this task would have been unfathomable in terms of both cost and complexity even two years ago'. In the past, scientists would only have been able to sequence the DNA from one gene at a time, so pinpointing such a tiny mutation would have been practically impossible.

The researchers then checked for the presence of the mutation in a further 89 adult-type granulosa cell tumours and found that it was present in 86 of them (97 per cent) compared to only ten to 20 per cent of other types of ovarian cancer. Most cancers are caused by a complex interaction of several genetic mutations, and so identifying a rare mutation that is the sole cause of a cancer type is extremely useful. Dr Dianne Miller, a cancer specialist at BC Cancer Agency and Vancouver General Hospital, said: 'This cancer is unique. For patients with this tumour type, it means they should all have the same response to the same treatment. And now that we have this pathway, we can look for existing cancer drugs that might work on this particular gene mutation to make the cancer disappear'.

Ovarian cancer affects around 7000 women in the UK each year and has high mortality rates as it is often diagnosed late when the cancer has spread to other parts of the body. Granulosa cell tumours account for only three to five per cent of ovarian cancers. Dr David Huntsman, who led the study, said: 'this discovery... clearly shows the power of the new generation of DNA sequencing technologies to impact clinical medicine...'.

Based upon our success in decoding granulosa cell tumours we are focusing on other rare tumours in what could be described as a guerrilla war on cancer.

We hope that these studies will not only help future patients with rare tumours but will also teach us about more common ones as well.'