Confused about BRCA, can someone please help me?

loveb

I'm a bit confused by the BRCA mutations and was hoping to be able to ask some questions here until I'm able to meet with a genetic counselor.

My Mom passed away last year from BC and two of her sisters have also battled BC. My Mom was tested for BRCA and both 1 and 2 came back with no mutation found. My cousin (my mom's sister's daughter) tested positive for BRCA1. I'm confused about a couple of things and was hoping someone may be able to help me understand.

1. Are there many false negatives to this test? Could my Mom have indeed been positive? I don't understand how all three sisters have breast cancer and I'm guessing my aunt (my Mom's sister) is BRCA1 positive or my cousin wouldn't have tested positive but my Mom still tested negative. I guess there is a chance my uncle was the carrier and passed it to my cousin but it just seems like there is obviously a family link on my Mom's side.

I did read a thread on this forum about false negatives but I'm not sure how common this may be.

2. If my Mom's test was accurate and she was indeed negative, is there still a chance I could test positive (assuming my dad is negative)?

3. I have not been tested and didn't think I needed to be since my Mom tested negative but do you think I should still explore testing?

Thank you very much for taking the time to read this. I most sincerely appreciate any guidance. 

GC1

These are all very good questions loveb.  Certainly a genetic counselor would be able to help you try to answer them.

Based on your family's history, it seems like there may be one of three situations.  Either:

1) There is a mutation in maternal family that your mother didn't have.  In that case, your mother would still be at the general population risk for breast cancer.  Her breast cancer would have been completely unrelated to the BRCA1 mutation in the family.

2) The mutation found in your cousin came from her father's family.  In that case, the breast cancers in your mother and aunts wouldn't be explained by the mutation found in your cousin.

3) The BRCA test comes in two steps.  Not everyone who has the test has the second part of the test.  It is possible that the mutation found in your cousin was found using the second test (called BART).  If your mother didn't have BART, then the mutation wouldn't be found and therefore her test would be negative.

So, in answer to your questions.  

Question 1 - False negatives are rare.  It is far more likely that your mother had a sporadic breast cancer (unrelated to a BRCA gene) even though others in the family had hereditary breast cancer (related to the BRCA mutation), especially if your mother was older when she developed her breast cancer.  

Question 2 - Assuming your dad is negative, this could occur if your cousin's mutation was one that was found using the BART test.  Otherwise, if your mother was negative, you would not be able to inherit a mutation she did not have.

Question 3 - This would depend on the type of testing your cousin had and your mother had.  If possible, bring copies of your mother's results and your cousin's results to your appointment with your genetic counselor.  They will be able to determine if testing should be considered.

I hope this helps! 

loveb

Thank you so much GC1. This was extremely helpful!

I most sincerly appreciate you taking the time to respond.

Latte

hi loveb,

was going to answer you, but gc1 covered  it really well. the one thing i would add is - even if you are BRCA negative, since you have a strong family history you should undergo regular screening to catch cancer early if you should get it. hope the genetics counsellor meeting goes well.