Which is the commonest malignancy of ovary?

Serous cystadenoma and cystadenocarcinoma are amongst the most common of cystic ovarian neoplasm, accounting about 50% of all ovarian tumors, of these 60% are benign, 15% borderline and 25% are malignant. Of the all cystic tumors of the ovary 5 to 10% are dermoids. Dermoid cyst is usually unilocular, with smooth surface seldom attaining more than 15 cm in diameter. Granulosa cell tumours are fairly common and represents 10% of all solid ovarian tumours. Ref: Shaw's Textbook of Gynaecology, 13th Ed, Page 358-359.