8mm complex cyst & 4mm lymph node in breast

I am a 45 year old with no personal history of cancer but my sister at age 60 was diagnosed with a very aggressive form of cancer. I had a digital mammo done and they saw the cyst and I went back and had another view and then an ultrasound. THe ultrasound did not show the same as the mammo in fact it didn't see it at all but it did see another area, so an MRI was ordered and on this there were actually 3 areas that showed up one being the 8mm complex cyst directly deep to the nipple in the 6 oclock position with no enhancement and there is a 4mm lymph in size and does show some enhancement. THe dr/radiologist said it was nothing I am feeling uneasy about this can someone explain to me what this means?
Should I have a biopsy or needle aspiration done as I have heard that is the only way you can truly tell if there are any cancer cells present.

Thank you

[Cleveland Clinic]

Dear stardust3:  Unfortunately, there is no perfect test to detect breast cancer (or rule it out).  Generally, the radiologist would take the findings of the mammogram, ultrasound and MRI as well as a clinical examination and determine the level of suspicion and whether further investigation should be undertaken.  MRI is generally too sensitive and leads to a lot of false positive results and unnecessary biopsies.  However, if you are concerned, you should discuss this again with your doctor to see if there is any cause to proceed with biopsy.