Thank you for the query.
You need to know that it if this cyst would be malignant, it would kill you before reaching half of mentioned size. So if it has reached 18 cm, most likely this is benign lesion what is a good news for you. However you should follow as advised by your gyneacologist.
One more thing, breast and ovarian cancer
in family makes you very suspicious of BRCA1/BRCA2
. Therefore, you should consult oncologist
or genetics and perform BRCA1/BRCA2 mutation tests.
Hope this will help.