The effect of carrying such a mutation on survival after developing breast or ovarian cancer is less well understood. We investigate the relationship between BRCA1 and BRCA2 carrier status and survival after breast cancer. We obtained data from the Cancer and Steroid Hormone Study, a large population-based study including over four thousand breast cancer cases.
Patient data includes extensive information about breast and ovarian cancer in relatives.
In the absence of genetic testing, for each individual presence or absence of mutation at a breast cancer susceptibility gene is captured by a pair of latent categorical variables whose probability depends on the patient's family history of breast and ovarian cancer. Inference is accomplished using a Markov chain Monte Carlo algorithm to draw a sample from the posterior distribution of model parameters accounting for sampling error, uncertainty in the genotype of study participants and uncertainty in estimates of genetic parameters. A combined-gene analysis estimates the effect on survival after breast cancer for women carrying any such genetic mutation. The analysis indicates that this effect, if present, may be positive. An analysis assessing the separate effects of the two genes indicates that carriers of BRCA2 may have an improved prognosis.