According to doctors women who have close relatives suffering from breast cancer but who may not have the main genetic mutations linked to the illness may still have a higher than average risk of developing the disease.
Research revealed that although they may test negative for the BRCA1 and BRCA2 faults, they may be three times more likely to be diagnosed with breast cancer by the age of 50 than other women.
Professor Gareth Evans, of St Mary's Hospital in Manchester, England, said, "Despite the fact they have not inherited the BRCA 1 or BRCA2 faults, they have a risk of inheriting other genetic faults, many of the genes of which we have not identified."
"Their chances of developing breast cancer under 50 were three times that in the general population."
According to Evans although the raised risk is relatively small, a rise from 2 percent to 6.4 percent women in families with a history of breast cancer should be given extra screening for the disease at a younger age -- probably starting at 35 years old.
In developed countries genetic mutations are found to be responsible for about five percent of breast cancer cases. According to scientists although changes in the BRCA1 and BRCA2 genes are the leading known causes, there may be many more genes involved.
Evans said, "We now know there may be 40 or 50 genes that increase breast cancer risk." "We are only dealing with the two that are the tip of the iceberg but underneath there is a whole raft of other genetic faults that may only slightly increase your risk."
Genetic faults in 531 close relatives mainly sisters and daughters, of 277 women with breast, ovarian or both cancers were tested by Evans and his team.
The researchers found that half of the women had negative results for the BRCA1 and BRCA2 , in addition to the 28 who developed breast cancer and four who were diagnosed with ovarian cancer. Four different BRCA1 and BRCA2 phenocopies in women who tested negative for the mutations.
A phenocopy happens when a patient tests negative for the genetic fault but develops the condition to which it predisposes them. The findings of the research have been published in the Journal of Medical Genetics. According to the researchers the phenocopy is probably due to other alterations, or modifier genes, that mimic the changes produced by the specific genetic fault.
Evans said, "It is clear it is not the simple story of you either carry a high-risk gene or you don't. It is a spectrum of risks due to a whole host of genetic factors."
He added, "Even when you are in a high-risk family with BRCA1 and BRCA2, you still have to take into account these other genetic factors that may be in those families."
The International Agency for Research on Cancer (IARC) in Lyon, France has found that breast cancer is the most common cancer in women, with more than a million cases detected worldwide each year.