This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Presentation (Carcinoma Ovary), Subject name: Gynaecology & Obstetrics
Which of the following is the most common malignant ovarian tumor? 
Select and explain. 
A. Serous cysadenocarcinoma, B. Mucinous tumor, C. Endometrioid tumor, D. Mesonephroid tumor
A: Serous cysadenocarcinoma
Answer: A: Serous cysadenocarcinoma 
Explanation: Ans. is 'a' i.e., Serous cystadenocarcinoma o Serous cysadenomas or cysadenocarcinomas form about 50% of all the ovarian tumors. Of these 60 - 70 % are benign, 15% borderline malignant, and 20 - 25% malignant. Thus serous cystadenocarcinomas form the most common malignant tumors of ovary.