Complex cysts and ovarian cancer

Hello-  I am 37 years old and had an ultrasound yesterday and they found a cyst on my left ovary, the right ovary and uterus  were fine except for a few fibroids. Nothing was detected during my internal this was done because of some breakthrough bleeding. I do not take birth control now but did for about 10 years. The technician orginally thought it was completely fluid filled until she did a transvaginal ultrasound at which point she said the cyst had a 'solid' component. From what have read that means it is a complex cyst. When I asked about the possiblity of cancer I was told it is impossibe to rule out with just the ultrasound.  A follow-up with my physician is scheduled for next week.  No one in my family has had ovarian cancer.My questions are:

How come it looked fluid filled externally but not transvaginally?
What is the connection between complex cysts and ovarian cancer?
If the cyst is cancerous is that the same as ovarian cancer?
Since the other ovary and uterus looked OK; would that mean any cancer would be confined to the left ovary or is that not possible to tell form an ultrasound?

Any insight you can provide would be apprecaited; I am trying not to worry but when someone says, 'cancer' even if they say not likely or rare, it can be scary.

Thanks,
GretchM