Understanding Conflicting Breast Biopsy Results: What to Do Next

Question
Hello.  I am 42 years old.  A lobulated mass was found on my first breast screening.  I was told that it was probably benign and to come back in 6 months.  I did that -the mass did not grow, but changed shape - looked even stranger even more lobulated. I decided to get a second opinion at a prestigious breast center.  They saw that it had some irregular borders and increased through transmission, and blood flow within the lesion, they wanted to do a biopsy.  Unfortunately, my insurance said no, and I had to go somewhere else.  Another institution core biopsied it, and it came back benign - a supposed fibroadenoma - Iwas surprised because it had some angular margins.  While giving me the US core biopsy, they found another lump - they did an FNA and the results came back with atypical ductal cells, loosely cohesive groups, prominent nucleoli, singly and mildly overlapping cells, macrophages.  So, they did a vacuum assisted biopsy for definitive results - this too was supposedly another fibroadenoma - however, because of the atypical cells they feel as though they need to surgically remove it to see what's really going on - my breast surgeon also wants to surgically remove the other lobulated mass - just to make sure (it was honestly strange looking to be benign).  So, can you please tell me why I am having so many conflicting results? Atypical cells on FNA and then benign on the US core biopsy of one lump, and then my films showing irregular/somewhat angular and lobulated borders on another mass with benign results from this core biopsy.  What could be the problem?  And, how often are benign core biopsy results wrong?

Answer
Both core and FNA biopsies are usually VERY reliable - in trained hands. But of course mishaps are not completely unknown. Here we are dealing with 2 different lesions too. I have no other explanation at present. I do agree that surgical biopsies of both lesions should be done in this situation!