Complex cysts in the breasts is one of the types apart from simple cysts. They are unevenly thick cysts which are filled with debris or even old blood clots unlike simple cysts that are filled with clear fluid. However, there is one thing that normally rings the alarm. Does complex cyst have a chance of leading to cancer? To answer this question, it is actually a very small chance of the connection it can have with breast cancer. This only means that the chances of a complex breast cyst being cancerous is actually low.