The estimation of cancer risk in individuals is of great interest for research teams. The kin-cohort
method is a method of choice for estimating hazards and penetrance of cancer, because of its capability to
illustrate the correlation between genotype and phenotype. In the estimation of cancer penetrance, many
models omit to take into account the fact that hazards are likely to increase, decrease, or remain constant
with respect to age variations. In order to estimate cancer penetrance by rectifying the said drawback of the
commonly used models , we utilized a modified piecewise exponential model using weibull distribution, i.e.
a piecewise Weibull model. We considered mutations in BRCA1 and BRCA2 genes, which are related to
ovarian and breast cancer. A set of data similar to true values was generated. We analyzed the data set
using both piecewise exponential and piecewise Weibull models. Our results showed that the Weibull
model was closer than the exponential model to the true values in terms of estimating the hazards and
penetrance and a significant difference between two models was recognized. For the persons who are at
risk of developing cancer, Due to the importance of the estimation of incidence probability, methods that
can generate most accurate estimations are preferable. Therefore, we recommend the piecewise Weibull
model as a proper model for the estimation of hazard and penetrance.