Mutation Probabilities and Cancer Risks

When you go in for genetic counseling you are interviewed about your family history of cancer. You provide a list of all of your siblings, parents, parents siblings, and grandparents including ages, and cancer occurrences and age of death of any that have passed. Based on this information, you are given probabilities for your chance of a mutation in a gene. I was getting counseling on only BRCA1, BRCA2 (breast cancer/ovarian cancer related) and MLH1, MSH2, and MSH6 (colorectal cancer related) genes  so these mutation probabilities only address those genes. You also receive a risk assessment of your likelihood of developing those cancers, and other cancers that may have occurred in your family history within a five year period or during your lifetime. As you can see my risk of developing breast cancer is 6.1%. Well I guess that one was a little wrong because i have it 100%!

Below each mutation probability are the results based on the different software algorithms. For example three different software algorithms (there are others that were not used) were examined on this assessment for the BRCA1 gene – Couch, Shattuck-Eidens, and BRCAPRO. They are all different because they take into account different populations in their predictions. In other words, one only considers families with two or more cases of breast cancer, one will result in the same probability regardless of whether there is one case or four cases of breast cancer, and one only looks at first and second degree relatives regardless of incidences of breast cancer. Which one is more reliable? I think it might depend on the specific family history because of the way the populations are examined. I’m not sure but from my reading they all largely underestimate probabilities.

I really don’t know if I explained that very well but that was my understanding from talking with the counselor and from further research. I do have one year of Research, Evaluation, Measurement and Statistics from UGA under my belt so it makes sense to me in my brain but i’m not sure if it came out correctly in my explanation. Do your own research if you really care.

Mutation Probabilities

Couch .117
Shattuck-Eidens .042
Myriad .047
MMRpro .014
MMRpro .015
MMRpro .004
MLH1 or MSH2
MMRpro (+MSH6) .033
Weijnen .004
Pancreas Gene .004

Cancer Risks

Type of Cancer 5 Year Lifetime
Breast .003 .061
Ovarian .001 .017
Colorectal .002 .042
Endometrial .001 .033
Pancreas .0 .013
Melanoma .002 .019