"The problem is that the most lethal form seems to be the most difficult to detect," says the head of the institute's cancer program Professor Georgia Chenevix-Trench.
"It seems to rise very quickly and give you a very narrow window of opportunity to make the diagnosis before it spreads."
A woman's lifetime risk of developing breast or ovarian cancer is greatly increased if she inherits a harmful mutation in BRCA1 or BRCA2.
The six new variants or "typos" identified have a more subtle impact than the BRCA1 and BRCA2 mutations, says Prof Chenevix-Trench.
"Individually, each of these typos increases the risk of cancer by a very small amount.
"However, if a woman carries a large number of these typos her risk of developing ovarian cancer may be as high as that conferred by mutations in BRCA1 or 2."
Actress Angelina Jolie has had a double mastectomy because she carries the faulty gene BRCA1.
"This finding would be particularly relevant to people like Angelina Jolie because in time we should be able to give much more precise estimates of what their ovarian cancer is and that should help them decide when they want to have prophylactic surgery, if at all."
- AAP