On gross pathological examination, they are solid, sharply circumscribed and pale yellow-tan in colour. 90% are unilateral (arising in one ovary, the other is unaffected). The tumours can vary in size from less than to . Borderline and malignant Brenner tumours are possible but each are rare.

Brenner tumors are an uncommon subtype of the surface epithelial-stromal tumor group of ovarian neoplasms. The majority are benign, but some can be malignant.

They are most frequently found incidentally on pelvic examination or at laparotomy. Brenner tumours very rarely can occur in other locations, including the testes.

They are exceptionally associated with hypercalcemia. On gross examination, dysgerminomas present with a smooth, bosselated (knobby) external surface, and is soft, fleshy and either cream-coloured, gray, pink or tan when cut. Microscopic examination typically reveals uniform cells that resemble primordial germ cells. Typically, the stroma contains lymphocytes and about 20% of patients have sarcoid-like granulomas.

Metastases are most often present in the lymph nodes.

A dysgerminoma is a type of germ cell tumor; it usually is malignant and usually occurs in the ovary.

A tumor of the identical histology but not occurring in the ovary may be described by an alternate name: seminoma in the testis or germinoma in the central nervous system or other parts of the body.

Dysgerminoma accounts for less than 1% of ovarian tumors overall. Dysgerminoma usually occurs in adolescence and early adult life; about 5% occur in pre-pubertal children. Dysgerminoma is extremely rare after age 50. Dysgerminoma occurs in both ovaries in 10% of patients and, in a further 10%, there is microscopic tumor in the other ovary.

Abnormal gonads (due to gonadal dysgenesis and androgen insensitivity syndrome) have a high risk of developing a dysgerminoma. Most dysgerminomas are associated with elevated serum lactic dehydrogenase (LDH), which is sometimes used as a tumor marker.

A germ cell tumor (GCT) is a neoplasm derived from germ cells. Germ cell tumors can be cancerous or non-cancerous tumors. Germ cells normally occur inside the gonads (ovary and testis). Germ cell tumors that originate outside the gonads may be birth defects resulting from errors during development of the embryo.

Mixed germ cell tumors occur in many forms. Among these, a common form is teratoma with endodermal sinus tumor.

Teratocarcinoma refers to a germ cell tumor that is a mixture of teratoma with embryonal carcinoma, or with choriocarcinoma, or with both. This kind of mixed germ cell tumor may be known simply as a teratoma with elements of embryonal carcinoma or choriocarcinoma, or simply by ignoring the teratoma component and referring only to its malignant component: embryonal carcinoma and/or choriocarcinoma. They can present in the anterior mediastinum.

Benign tumors of the ovary include ovarian cysts, such as borderline tumor cysts.

The tumour is subdivided into many different subtypes. The most typical is composed of tubules lined by Sertoli cells and interstitial clusters of Leydig cells.

Due to excess testosterone secreted by the tumour, one-third of female patients present with a recent history of progressive masculinization. Masculinization is preceded by anovulation, oligomenorrhoea, amenorrhoea and defeminization. Additional signs include acne and hirsutism, voice deepening, clitoromegaly, temporal hair recession, and an increase in musculature. Serum testosterone level is high.

Thecomas or theca cell tumors are benign ovarian neoplasms composed only of theca cells. Histogenetically they are classified as sex cord-stromal tumours.

They are typically estrogen-producing and they occur in older women (mean age 59; 84% after menopause). (They can, however, appear before menopause.)

60% of patients present with abnormal uterine bleeding, and 20% have endometrial carcinoma.

Fibroepithelial neoplasms (or tumors) are biphasic tumors. This means they consist of epithelial tissue, and stromal or mesenchymal tissue. They may be benign or malignant.

Examples include:

- Brenner tumor of the Ovary

- Fibroadenoma of the Breast

- Phyllodes tumor of the Breast

Epithelial-stromal tumors are classified on the basis of the epithelial cell type, the relative amounts of epithelium and stroma, the presence of processes, and the location of the epithelial elements. Microscopic pathological features determine whether a surface epithelial-stromal tumor is benign, borderline, or malignant (evidence of malignancy and stromal invasion). Borderline tumors are of uncertain malignant potential.

This group consists of serous, mucinous, endometrioid, clear cell, and brenner (transitional cell) tumors, though there are a few mixed, undifferentiated and unclassified types.

Granulosa cell tumours (or granulosa-theca cell tumours or folliculoma) are tumours that arise from granulosa cells. These tumours are part of the sex cord-gonadal stromal tumour or non-epithelial group of tumours. Although granulosa cells normally occur only in the ovary, granulosa cell tumours occur in both ovaries and testicles (see Ovarian cancer and Testicular cancer). These tumours should be considered malignant and treated in the same way as other malignant tumours of ovary. The ovarian disease has two forms, juvenile and adult, both characterized by indolent growth, and therefore has high recovery rates.

The staging system for these tumours is the same as for epithelial tumours and most present as stage I. The peak age at which they occur is 50–55 years, but they may occur at any age.

Juvenile granulosa cell tumour is a similar but distinct rare tumour. It too occurs in both the ovary and testis. In the testis it is extremely rare, and has not been reported to be malignant. Although this tumour usually occurs in children (hence its name), it has been reported in adults.

Ovarian tumors, or ovarian neoplasms, are tumors arising from the ovary. They can be benign or malignant (ovarian cancer).

Benign and borderline variants of this neoplasm are rare, and most cases are malignant.

These tumors may have a worse prognosis than serous tumors.

"Benign" serous tumours are unilocular (have one lobe); however if very large may be multilocular, contain clear fluid and have a smooth lining composed of columnar epithelial cells with cilia. On gross examination, the serous tumor may present as either a cystic lesion in which the papillary epithelium is contained within a few fibrous walled cysts, or the papillary projections may be away from the surface epithelium. Surgery is curative.

Estrogens are produced by "functioning" tumours, and the clinical presentation depends on the patient's age and sex.

- Female

- If the patient is postmenopausal, she usually presents with abnormal uterine bleeding, and in some cases hemoperitoneum.

- If the patient is of reproductive age, she would present with menometrorrhagia. However, in some cases she may stop ovulating altogether.

- If the patient has not undergone puberty, early onset of puberty may be seen.

- these tumors tend to have late recurrencies ( even after 30 years )

Dysgerminoma is the most common type of malignant germ cell ovarian cancer. Dysgerminoma usually occurs in adolescence and early adult life; about 5% occur in pre-pubertal children. Dysgerminoma is extremely rare after age 50. Dysgerminoma occurs in both ovaries in 10% of patients and, in a further 10%, there is microscopic tumor in the other ovary.

Seminoma is the second most common testicular cancer; the most common is mixed, which may contain seminoma.

Abnormal gonads (due to gonadal dysgenesis and androgen insensitivity syndrome) have a high risk of developing a dysgerminoma. Most dysgerminomas are associated with elevated serum lactic dehydrogenase (LDH), which is sometimes used as a tumor marker.

Metastases are most often present in the lymph nodes.

The term "germinoma" most often refers to a tumor in the brain that has a histology identical to two other tumors: dysgerminoma in the ovary and seminoma in the testis. Since 1994, MeSH has defined germinoma as "a malignant neoplasm of the germinal tissue of the gonads; mediastinum; or pineal region" and within its scope included both dysgerminoma and seminoma. Collectively, these are the seminomatous or germinomatous tumors.

Mucinous tumors are part of the surface epithelial-stromal tumor group of ovarian neoplasms, and account for approximately 36% of all ovarian tumors.

Approximately 75% are benign, 10% are borderline and 15% are malignant.

Rarely, the tumor is seen bilaterally; approximately 5% of primary mucinous tumors are bilateral.

"Benign" mucinous tumors are typically multilocular (have several lobes), and the cysts have a smooth lining of epithelium that resembles endocervical epithelial cells with small numbers of gastrointestinal-type epithelial cells.

"Borderline" and "malignant" mucinous tumors often have papillae and solid areas.

There may also be hemorrhage and necrosis.

It is well documented that malignancy may be only focally present in mucinous neoplasms of the ovary, so thorough sampling is imperative.

The major distinguishing features of mucinous tumors are that the tumors are filled with a mucus-like material, which gives them their name; this mucus is produced by mucus-secreting goblet cells very similar to the cells lining normal intestine.

These tumors may become very large, some have been weighed as large as 25 kilograms.

Cystadenocarcinomas (malignant tumors) contain a more solid growth pattern with the hallmarks of malignancy: cellular atypia and stratification, loss of the normal architecture of the tissue, and necrosis. The appearance can look similar to colonic cancer.

Clear stromal invasion is used to differentiate borderline tumors from malignant tumors.

Pseudomyxoma peritonei may present as a result of an ovarian mucinous tumor, however this is a rare cause of this condition, which is a rare condition. A more common cause of pseudomyxoma peritonei is a mucin-producing tumor of the appendix.

Since mucinous tumors arising from the ovary usually only involve one ovary, the presence of involvement in both ovaries with a mucinous tumor suggests that the tumor may have arisen in another location, and further study is warranted.

The risk of mucinous tumors is significantly associated with smoking: relative risk for current smokers 2.22 (2.22 times the risk for non-smokers) and 2.02 for past smokers. Risk is also associated with smoking duration: relative risk per 20 years was 1.44. See article by Tworoger SS in Cancer March 1, 2008 using data from the Nurses Health Study.

Serous tumours are part of the surface epithelial-stromal tumour group of ovarian neoplasms, which derive from Mullerian epithelium.

They are common neoplasms with a strong tendency to bilaterality, and they account for 50% of all ovarian tumours.

Sixty percent are benign (cystadenoma), 10% are borderline and 30% are malignant (cystadenocarcinoma).

Surface epithelial-stromal tumors are a class of ovarian neoplasms that may be benign or malignant. Neoplasms in this group are thought to be derived from the ovarian surface epithelium (modified peritoneum) or from endometrial or Fallopian tube (tubal) tissue. Tumors of this type are also called ovarian adenocarcinoma. This group of tumors accounts for 90% to 95% of all cases of ovarian cancer. Serum CA-125 is often elevated but is only 50% accurate so it is not a useful tumor marker to assess the progress of treatment.

Typically, they are cystic neoplasms with polypoid masses that protrude into the cyst. On microscopic pathological examination, they are composed of cells with clear cytoplasm (that contains glycogen) and "hob nail" cells (from which the glycogen has been secreted). The pattern may be glandular, papillary or solid.

There are few early warning signs that a patient has a DSRCT. Patients are often young and healthy as the tumors grow and spread uninhibited within the abdominal cavity. These are rare tumors and symptoms are often misdiagnosed by physicians. The abdominal masses can grow to enormous size before being noticed by the patient. The tumors can be felt as hard, round masses by palpating the abdomen.

First symptoms of the disease often include abdominal distention, abdominal mass, abdominal or back pain, gastrointestinal obstruction, lack of appetite, ascites, anemia, and/or cachexia.

Other reported symptoms include unknown lumps, thyroid conditions, hormonal conditions, blood clotting, kidney or urological problems, testicle, breast, uterine, vaginal, or ovarian masses.

The majority of Leydig cell tumors are found in males, usually at 5–10 years of age or in middle adulthood (30–60 years). Children typically present with precocious puberty. Due to excess testosterone secreted by the tumour, one-third of female patients present with a recent history of progressive masculinization. Masculinization is preceded by anovulation, oligomenorrhea, amenorrhea and "defeminization". Additional signs include acne and hirsutism, voice deepening, clitoromegaly, temporal hair recession, and an increase in musculature. Serum testosterone level is high.

In men testicular swelling is the most common presenting feature. Other symptoms depend on their age and the type of tumour. If it is secreting androgens the tumour is usually asymptomatic, but can cause precocious puberty in pre-pubertal boys. If the tumour secretes oestrogens it can cause feminisation in young boys. In adults, this causes a number of problems including gynaecomastia, erectile dysfunction, infertility, feminine hair distribution, gonadogenital atrophy, and a loss of libido.