Ovarian tumours are relatively common and account for ~6% of female malignancies. This article focuses on the general classification of ovarian tumours. For specific tumour features, please refer to the relevant subarticles.

Pathology

Subtypes

Primary ovarian tumours

Surface epithelial-stromal ovarian tumours (60-70%):

• ovarian serous tumours
  • ovarian serous cystadenoma: ~60% of serous tumours  
  • ovarian borderline serous cystadenoma: ~15% of serous tumours
  • ovarian serous cystadenocarcinoma: ~25% of serous tumours; commonest malignant ovarian tumour
• ovarian mucinous tumours: ~20% of all ovarian tumours ¹¹
  • ovarian mucinous cystadenoma: ~80% of mucinous tumours
  • ovarian borderline mucinous cystadenoma: 10-15% of mucinous tumours
  • ovarian mucinous cystadenocarcinoma: 5-10% of mucinous tumours
• ovarian endometrioid tumour: 8-15% of all ovarian tumours
• clear cell ovarian carcinoma: ~5% of ovarian cancer
• Brenner tumour: ~2.5% of ovarian epithelial neoplasms
• squamous cell carcinoma of the ovary
• ovarian cystadenofibroma* / ovarian adenofibroma: can be serous, mucinous, endometrioid, clear cell or mixed
• ovarian cystadenocarcinofibroma: extremely rare
• ovarian fibrosarcoma
• undifferentiated carcinoma of the ovary: ~4% of all ovarian tumours

* sometimes classified as a separate category rather than under epithelial ⁷

Germ cell ovarian tumours (~20%):

• ovarian teratoma: the commonest primary benign tumour of the ovary
  • mature ovarian (cystic) teratoma
  • immature ovarian teratoma
  • specialised teratomas of the ovary
    • struma ovarii tumour
    • ovarian carcinoid tumours
• ovarian dysgerminoma
• ovarian yolk sac tumour: endodermal sinus tumour
• ovarian embryonal carcinoma
• ovarian choriocarcinoma: <1% of ovarian tumours
  • pure primary ovarian choriocarcinoma: extremely rare ²
• malignant mixed germ cell tumour of the ovary

Sex cord / stromal ovarian tumours (8-10%):

• ovarian fibrothecoma: ~5% of ovarian tumours
  • ovarian fibroma: ~4% of ovarian tumours
  • ovarian thecoma: ~1% of ovarian tumours
• sclerosing stromal tumour of the ovary: rare ⁹
• ovarian Sertoli-Leydig cell tumour - ovarian androblastoma: ~0.5% of ovarian tumours
• granulosa cell tumour of the ovary: commonest malignant sex cord tumour
  • juvenile granulosa cell tumour of the ovary
  • adult granulosa cell tumour of the ovary
• small cell carcinoma of the ovary ¹⁵

Mixed

These are uncommon:

• collision tumours of the ovary
• ovarian carcinosarcoma <1% 

Other

• ovarian lymphoma
  • primary ovarian lymphoma
  • secondary involvement of the ovary with lymphoma
• metastases to the ovary
  • Krukenberg tumour
  • other metastatic lesions to the ovary

Classification according to morphology

Predominantly cystic

• serous cystadenoma
• mucinous cystadenoma 
• mature cystic teratoma
• serous cystadenocarcinoma
• mucinous cystadenocarcinoma

Predominantly solid

• Brenner tumour
• thecoma
• fibroma
• endometroid granulosa cell tumours
• dysgerminoma
• endodermal sinus tumour (yolk sac tumour)
• metastatic

Serological tests

• CA-125 levels: elevated in most ovarian malignancies (~80% in general); some mucinous and germ cell tumours may not secrete this marker
• AFP levels: elevated particularly with immature ovarian teratomas (~50% of cases) and ovarian yolk sac tumours
• β HCG: in a small number of dysgerminomas
• human epididymis protein 4 (HE4): elevated in malignant ovarian diseases, being helpful to complement the Ca-125 in premenopausal women 

Risk factors

General risk factors include

• nulliparity
• early menopause 
• gonadal dysgenesis
• family history: contributes to 24% of cases of epithelial ovarian cancer¹⁴
  • BRCA1/BRCA2 mutations: particularly for serous types
  • Lynch syndrome-associated ovarian cancers most often have an endometrioid or serous type histology ¹⁴
• smoking: especially for mucinous adenocarcinoma
• previous history of breast, endometrial or colon cancer (Lynch II)
• certain ethnic groups

Protective factors

• oral contraceptives (OCP)
• breastfeeding (however this is controversial)

Risk assessment

• risk of malignancy index in ovarian tumours

Staging

The FIGO staging system is used for almost all of ovarian cancers: see ovarian cancer staging.