A cystadenocarcinoma is a cyst that is malignant. Most radiologists will not decisively say that a cyst is 100% benign (or malignant) when they read a CT or ultrasound, because they can't tell for sure until they open you up and look (and then send the cyst to pathology.) Most times if you have a cyst they will have what's called a differential diagnosis that includes cystadenoma (benign cyst) AND cystadenocarcinoma (malignant cyst.) I, too had both on my CT report and mine was BENIGN! Yay! You doc will be able to tell you if there are certain characteristics of the cyst that are of concern, however. GOod luck!
From what I have been reading about ovarian cancer, it is a type of ovarian cancer. If you put ovarian cancer thru a search engine, you see the different type of OVCA and their cahracteristics. Only bx can say it si malignant, though.