Figure 4.

Under the multiplicative polygenic model and the logistic model for lifetime risk of breast cancer (Figure 2), the distribution of lifetime risk is shown as a function of the cumulative proportion of the population. For the great majority of women in the population (indicated by the solid blue line), their lifetime risk is low (for example, 70% have a lifetime risk below the population average of 11%) and less than 10% have a lifetime risk in excess of 40%. For randomly selected women with a genetic variant associated with, on average, a 2-fold increased risk (indicated by the dashed blue line), the median lifetime risk is about the average population risk and about one-quarter have a lifetime risk in excess of 40%. For women with a strong family history equivalent to a 3-fold increased risk (indicated by the solid red line), nearly 80% are above average population risk and nearly half have a lifetime risk in excess of 40%. For those with a strong family history who also have a genetic variant associated with, on average, a 2-fold increased risk (indicated by the dashed red line), 90% are above population average risk and over 70% have a lifetime risk in excess of 40%.