Risks identified by deCODE BreastCancer™
The deCODE BreastCancer™ test assesses the genetic risk of breast cancer by testing for genetic risk variants that are very common in the population, each of which contribute relatively little, but that when combined can have a significant effect.
The deCODE BreastCancer™ test determines whether the subject has inherited the risk or non-risk version at 7 different variable sites in the human genome. By comparing deCODE BreastCancer™ to the general risk of women in the population it can be seen whether the person tested has a risk greater or lower than average population risk. The risks at each of the 7 markers are multiplied together to define combined risks of from 0.4- to about 4.0-fold the relative general population risk. The deCODE BreastCancer™ test examines only genetic risk factors, so other factors such as age and hormonal factors need to also be taken into account. By combining the test results and risks associated with other known risk factors a more complete lifetime risk estimate can be generated.
Based on an individual’s genotypes for the markers, lifetime genetic risk of being diagnosed with breast cancer can be determined and related to the general risk of breast cancer in the population. The deCODE BreastCancer™ test reports the subject’s measured genetic risk of breast cancer relative to the average population and the lifetime risk of being diagnosed with breast cancer.
The relative genetic risk of breast cancer compared to the general population determined by the test can vary from 0.45 for subjects who no risk variants at the 7 markers, to 3.77 for subjects who have 2 risk variants (1 on each chromosome) at all markers.
About 42% of the female population has genotype combinations of the tested markers that confer an increased relative risk (>1) of breast cancer. Ten percent of women in the general population have genotypes that confer a more than 40% increase in the relative risk of breast cancer, about 5% would be considered high risk with a 1.66-fold or greater risk (corresponding to a lifetime risk of 20% or greater), and approximately 1% of women have, on average, a 3-fold risk (37% lifetime risk of breast cancer).
The risk distribution in the general population and the proportion of the population with decreased (<1) and increased (>1) risks according to the test are given in the figure below:
In basic terms, carrying a high-risk deCODE BreastCancer™ genetic profile does not necessarily mean that a woman will develop breast cancer, just as having a low-risk genetic profile does not eliminate the possibility of getting the disease. Rather, these genetic risk variants impact the likelihood that she will develop breast cancer. Nongenetic risk factors such as current age, age at menarche, age at first live birth, hormonal history and status, history of exposure of the chest wall to X-rays, and previous benign or malignant breast disease may also affect a woman’s risk of breast cancer. Genetic and nongenetic risk factors all need to be taken into account when judging the overall breast cancer risk of an individual.