Cysts larger than 5cm and that are complex are worrisome for
ovarian cancer. But, the only way to know for sure is to have the mass removed and biopsied. Also, cysts or masses in postmenopausal women are more worrisome for cancer than ones in younger women. I have a neighbor friend who had an 8cm complex mass in her 60's and it was benign. Yet, I had a 6cm, complex mass in my 30's and it was malignant. Ovarian cancer is tricky because it is different for everyone.