My mother was diagnosed with breast cancer at 54, grandmother had pancreatic cancer at 70 and great aunt had colon cancer at 65. No one else has cancer in my large family. Could I have the brca gene?

Very Low Risk. The risk of having a brca mutation can be estimated at: http://www.Myriadpro.Com/brca-risk-calculator/calc.Html. A woman with ashkenazi jewish heritage and this family history would have about an 8% chance of having a brca mutation. Without ashkenazi heritage the risk drops to 1.5%. The best way to know for sure would be to have your mother see a genetic counselor and consider having testing.
Not too likely but. If your mother's cancer was "triple negative" and if she's still alive (which i truly hope), she fulfills criteria for testing. Recently, pancreatic cancer was added to the criteria so if she can't or won't test, you should discuss this with your doc. Best to you.
Probably no. This test is most useful if there is more than one member of the family with breast cancer and or ovarian cancer. Furthermore this type of breast cancer ooccurs below the age of 45 years. So I do not think it would be useful for you to do this test......It is also quite expensive to do this test..