Complex Cysts ??? More likely to be cancerous??

I had a Mammogram today and was told that I had a complex cyst behind my left nipple. They want to do a needle biopsy in two days.I have no family history and don't understand the difference between simple cyst and complex cysts??? Hoping someone can clue me in to difference.

Thanks

[Cleveland Clinic]

Dear weez1966:  A simple cyst is a fluid filled structure that is benign by definition.  A complex cyst is also fluid filled but there are septations (or walls) within the structure that are solid.  While most complex cysts are also benign, there can be concern about the nature of the solid components and whether they have formed around areas of concern.  In this case, a radiologist may recommend biopsy or excision.