Tumors of the ovary can either be benign (non-cancerous) or malignant (cancerous). There are certain tumors that are classified as atypical (uncertain or unspecified behavior) meaning that some behave in a benign manner, or some behave in a malignant manner. A majority of the ovarian tumors diagnosed via lab studies (biopsy) are benign.

The World Health Organization (WHO) is an authoritative body that compiles, prepares, and publishes histological and molecular classification of tumors, via their Blue Books, based on research inputs from experts worldwide. These reference books chiefly aid in global cancer research, provide gold standards for tumor diagnosis, and help in treating cancer patients.

According to the WHO Classification of Female Genital Tumors (2020), 5th Ed., Vol. 4, benign and malignant tumors of the ovary are classified in the following manner:

Tumors of the ovary:

Serous tumors

• Benign serous tumors
  • Serous cystadenoma, adenofibroma, and surface papilloma of the ovary
• Borderline serous tumors
  • Serous borderline tumor of the ovary
• Malignant serous tumors
  • Low-grade serous carcinoma of the ovary
  • High-grade serous carcinoma of the ovary

Mucinous tumors

• Benign mucinous tumors
  • Mucinous cystadenoma and adenofibroma: Benign Mucinous Cystadenoma of Ovary is a common benign ovarian tumor that generally affects women in their fourth decade
• Borderline mucinous tumors
  • Mucinous borderline tumor
• Malignant mucinous tumors
  • Mucinous carcinoma of the ovary

Endometrioid tumors

• Benign endometrioid tumors
  • Endometrioid cystadenoma and adenofibroma: Benign Endometrioid Cystadenoma of Ovary is a common benign ovarian tumor that generally affects middle aged women
• Borderline endometrioid tumors
  • Endometrioid borderline tumor: It is an ovarian tumor with low or borderline malignant potential. The tumor is seen in women of a wide age range
• Malignant endometrioid tumors
  • Endometrioid carcinoma of the ovary

Clear cell tumors

• Benign clear cell tumors
  • Clear cell cystadenoma and adenofibroma
• Borderline clear cell tumors
  • Clear cell borderline tumor
• Malignant clear cell tumors
  • Clear cell carcinoma of the ovary

Seromucinous tumors

• Benign seromucinous tumors
  • Seromucinous cystadenoma and adenofibroma
• Borderline seromucinous tumors
  • Seromucinous borderline tumor
• Malignant seromucinous tumors
  • Seromucinous carcinoma

Brenner tumors

• Benign Brenner tumors
  • Brenner tumor
• Borderline Brenner tumors
  • Borderline Brenner tumor
• Malignant Brenner tumors
  • Malignant Brenner tumor

Other carcinomas

• Mesonephric-like adenocarcinoma
• Undifferentiated and dedifferentiated carcinomas of the ovary
• Carcinosarcoma of the ovary
• Mixed carcinoma of the ovary

Mesenchymal tumors

• Endometrioid stromal sarcoma of the ovary
• Smooth muscle tumors of the ovary
• Ovarian myxoma
• Other ovarian mesenchymal tumors

Mixed epithelial and mesenchymal tumors

• Mixed malignant epithelial and mesenchymal tumors
  • Adenosarcoma of the ovary

Sex cord-stromal tumors

• Pure stromal tumors
  • Ovarian fibroma
  • Thecoma
  • Luteinized thecoma associated with sclerosing peritonitis
  • Sclerosing stromal tumor
  • Microcystic stromal tumor
  • Signet-ring stromal tumor
  • Leydig cell tumor
  • Steroid cell tumor
  • Ovarian fibrosarcoma
• Pure sex cord tumors
  • Adult granulosa cell tumor
  • Juvenile granulosa cell tumor
  • Sertoli cell tumor
  • Sex cord tumor with annular tubules
• Mixed sex cord-stromal tumors
  • Sertoli-Leydig cell tumor: It is a rare tumor arising from the sex cord cells present in the ovary. The tumor is typically seen in young adult women
  • Sex cord-stromal tumor NOS
  • Gynandroblastoma

Germ cell tumors

• Mature teratoma of the ovary: It is made up of cells that resemble adult tissue cells. Most teratoma tumors belong to the mature type. It is usually observed in young women and those in the child-bearing age
• Immature teratoma of the ovary: It is made up of cells that resemble an embryo, or a developing fertilized egg. These tumors are less commonly observed and tend to affect younger populations
• Dysgerminoma: It is a rare malignant tumor of the ovary that is generally seen in girls and young adult women
• Yolk sac tumor
• Embryonal carcinoma
• Non-gestational choriocarcinoma
• Mixed germ cell tumor of the ovary
• Monodermal teratomas and somatic-type tumors arising from a dermoid cyst
  • Struma ovarii: It is an infrequently observed mature teratoma that typically benign but may transform into a malignancy. The tumor is seen in women above 40
  • Ovarian carcinoid
  • Neuroectodermal-type tumors
  • Monodermal cystic teratoma
  • Somatic neoplasms arising from teratomas

• Germ cell-sex cord-stromal tumors
  • Gonadoblastoma
  • Mixed germ cell-sex cord-stromal tumor, unclassified

Miscellaneous tumors

• Rete cystadenoma, adenoma, and adenocarcinoma
• Wolffian tumor of the ovary
• Solid pseudopapillary tumor
• Small cell carcinoma of the ovary, hypercalcemic type
• Wilms tumor

Mesothelial tumors

Tumor-like lesions

• Follicle cyst
• Corpus luteum cyst
• Large solitary luteinized follicle cyst
• Hyperreactio luteinalis
• Pregnancy luteoma
• Stromal hyperplasia and hyperthecosis
• Fibromatosis and massive edema
• Leydig cell hyperplasia

Metastases

• Metastases to the ovary

Additional ovarian tumor articles (on DoveMed) that are not part of WHO Classification of Female Genital Tumors:

Angiomyolipoma of Ovary: It is an extremely uncommon extrarenal angiomyolipoma that is present in adult women. An angiomyolipoma is a benign tumor that is a mixture of blood vessels, smooth muscles, and fat.

Arrhenoblastoma of Ovary: It is a rare tumor of the ovary that mainly affects young adult women.

Benign Endometrioid Adenofibroma of Ovary: It is a benign ovarian tumor that generally affects young adult women. The cause of tumor formation is unknown.

Benign Endometrioid Cystadenofibroma of Ovary: It is a common benign ovarian tumor that generally affects middle-aged women. The cause of tumor formation is unknown.

Benign Mucinous Adenofibroma of Ovary: It is a common benign ovarian tumor that generally affects young adult women. The cause of tumor formation is unknown.

Benign Mucinous Cystadenofibroma of Ovary: It is a benign ovarian tumor that generally affects young adult women. The cause of tumor formation is unknown.

Benign Serous Cystadenofibroma of Ovary: It is a common benign ovarian tumor that generally affects middle-aged women. The cause of tumor formation is unknown.

Benign Teratoma of Ovary: It is a form of mature teratoma that is mostly observed in females below 30 years of age.

BRCA 1/2-Associated Hereditary Breast and Ovarian Cancer Syndrome: It is a malignant condition inherited in an autosomal dominant manner. Individuals with this condition have germline mutations in the BRCA1 and BRCA2 genes which increases the risk of developing breast and ovarian cancer.

Clear Cell Adenocarcinoma of Ovary: It is a rare malignant ovarian tumor that generally affects middle-aged women. The cause of tumor development is unknown.

Dermoid Cyst of Ovary: It is a type of mature cystic teratoma. It is the most common germ cell tumor involving the ovary. The cyst is often seen in young girls and young women.

Malignant Mesothelioma of Ovary: It is an extremely uncommon, malignant tumor of the ovary. The tumor is seen in a wide age group of women.

Malignant Teratoma of Ovary: It is a form of immature teratoma that is mostly observed in females below 20 years of age.

Monodermal Teratoma of Ovary: It is an uncommon form of teratoma that originates from a single germ cell layer. The tumor may be observed in girls and women.

Mucinous Adenocarcinoma of Ovary: It is a common malignant ovarian tumor that generally affects middle-aged women. The cause of tumor development is unknown.

Mucinous Cystadenocarcinoma Fibroma of Ovary: It is a malignant ovarian tumor that generally affects middle-aged women. The cause of tumor development is unknown.

Ovarian Mucinous Borderline Tumor of Endocervical Type: It is a rare ovarian tumor with low or borderline malignant potential. The tumor may be noted in young and middle-aged women.

Ovarian Mucinous Borderline Tumor of Intestinal Type: It is a rare ovarian tumor with low or borderline malignant potential. The tumor may be noted in young and middle-aged women.

Serous Papillary Cystadenoma of Ovary: It is a common benign ovarian tumor that generally affects middle aged women. The cause of tumor development is unknown.

Teratoma of Ovary: It is a rare type of ovarian tumor that arises from the germ cells. It is usually observed in adolescent and young women.