Twin sister has breast cancer

My identical twin sister (46y.o.) has recently been diagnosed with DCIS and invasive moderatly differentiated ductal carcinoma. Should I be genetically tested for it or should she? What are the odds that I too will get it? If I should be tested what exactly should I ask to be tested for? Thank you.

[CCF-RN,MSN-rf]

Dear Twin: When a young person develops breast cancer, there is concern that it may be due to a genetic mutation.  If it is decided to test for such a mutation, the sister WITH the cancer would be tested first.  If this comes back positive, then it would make sense to confirm it in the twin, although the assumption is that it would be positive as well.  Genetic mutations tend to correlate most with young age (35-40) and numbers of family members.  So, in your case, it may be recommended for your sister to be genetic tested.  This is a complex issue and it would be to her/your advantage to see a genetic counselor to discuss this in greater detail.  They are best equipped to calculate relative risk.