No. Simple breast cysts are benign and cannot become cancers.
No. Cysts are a common condition, especially in women 35-50. The biggest problem with cysts is that it is impossible to differentiate them from tumors by physical examination or mammography; ultrasound or needle aspiration is necessary. Very rarely, breast cancers grow so fast that the center of the tumor can become liquified and resemble a cyst; either of these techniques should determine this.