Polyembryoma is a rare, very aggressive form of germ cell tumor usually found in the ovaries. Polyembryoma has features of both yolk sac tumour and undifferentiated teratoma/embryonal carcinoma, with a characteristic finding of embryoid bodies lying in a loose mesenchymal stroma.

It has been found in association with Klinefelter syndrome.

The ovarian fibroma, also fibroma, is a benign sex cord-stromal tumour.

Ovarian fibromas represent 4% of all ovarian neoplasms. They tend to occur mostly during perimenopause and postmenopause, the median age having been reported to be about 52 years, and they are rare in children. Lesions tend to be asymptomatic. If symptoms are present, the most common one is abdominal pain.

On gross pathology, they are firm and white or tan. On microscopic examination, there are intersecting bundles of spindle cells producing collagen.

There may be thecomatous areas (fibrothecoma). The presence of an ovarian fibroma can cause ovarian torsion in some cases.

Mucinous cystadenomas may be found in the:

- Ovary - ovarian mucinous cystadenoma

- Pancreas - pancreatic mucinous cystadenoma

- Peritoneum - peritoneal mucinous cystadenoma

- Liver - mucinous cystadenoma of the liver

- Vermiform appendix - appendiceal mucinous cystadenoma (see cystadenoma)

Teratomas maybe found in babies, children, and adults. Teratomas of embryonal origin are most often found in babies at birth, in young children, and, since the advent of ultrasound imaging, in fetuses.

The most commonly diagnosed fetal teratomas are sacrococcygeal teratoma (Altman types I, II, and III) and cervical (neck) teratoma. Because these teratomas project from the fetal body into the surrounding amniotic fluid, they can be seen during routine prenatal ultrasound exams. Teratomas within the fetal body are less easily seen with ultrasound; for these, MRI of the pregnant uterus is more informative.

Variants with edema can be associated with Meigs' syndrome. They may be a part of nevoid basal cell carcinoma syndrome (Gorlin syndrome).

A teratoma is a tumor made up of several different types of tissue, such as hair, muscle, or bone. They typically form in the ovaries, testicles, or tailbone and less commonly in other areas. Symptoms may be minimal if the tumor is small. A testicular teratoma may present as a painless lump. Complications may include ovarian torsion, testicular torsion, or hydrops fetalis.

They are a type of germ cell tumor (a tumor that begins in the cells that give rise to sperm or eggs). They are divided into two types mature and immature. Mature teratomas include dermoid cysts and are generally benign. Immature teratomas may be cancerous. Most ovarian teratomas are mature. In adults, testicular teratomas are generally cancerous. Definitive diagnosis is based on a tissue biopsy.

Treatment of tailbone, testicular, and ovarian teratomas is generally by surgery. Testicular and immature ovarian teratomas are also frequently treated with chemotherapy.

Teratomas occur in the tailbone in about 1 in 30,000 newborns making them the most common tumor in this age group. Females are affected more often than males. Ovarian teratomas represent about a quarter of ovarian tumors and are typically noticed during middle age. Testicular teratomas represent almost half of testicular cancers. They can occur in both children and adults. The term comes from the Greek words for "monster" and "tumor".

Papillary serous cystadenocarcinomas may exhibit psammoma bodies upon histopathology.

Ovarian serous cystadenoma, also (less precisely) known as serous cystadenoma, is the most common ovarian neoplasm, representing 20% of ovarian neoplasms, and is benign.Human Reproduction. University of Utah Medpath http://library.med.utah.edu/kw/human_reprod/seminars/seminar4B2.html.

It has a very superficial resemblance to the most common type of ovarian cancer (serous carcinoma of the ovary) under the microscope; however, (1) it is virtually impossible to mix-up with its malignant counterpart (serous carcinoma), and (2) does not share genetic traits of indeterminate serous tumours, also called "serous borderline tumours", that may transform into serous carcinoma.

Serous cystadenomas (of the ovary) are not related to serous cystadenomas of the pancreas, i.e. the presence of an ovarian "or" pancreatic one does "not" suggest an increased risk for the other one.

Papillary serous cystadenocarcinomas are the most common form of malignant ovarian cancer making up 26 percent of ovarian tumours in women aged over 20 in the United States.

As with most ovarian tumours, due to the lack of early signs of disease these tumours can be large when discovered and have often metastasized, often by spreading along the peritoneum.

Sex cord–gonadal stromal tumour (or sex cord–stromal tumour) is a group of tumors derived from the stromal component of the ovary and testis, which comprises the granulosa, thecal cells and fibrocytes. In contrast, the epithelial cells originate from the outer epithelial lining surrounding the gonad while the germ cell tumors arise from the precursor cells of the gametes, hence the name germ cell. In humans, this group accounts for 8% of ovarian cancers and under 5% of testicular cancers. Their diagnosis is histological: only a biopsy of the tumour can make an exact diagnosis. They are often suspected of being malignant prior to operation, being solid ovarian tumours that tend to occur most commonly in post menopausal women.

This group of tumours is significantly less common than testicular germ cell tumours in men, and slightly less common than ovarian germ cell tumours in women (see Ovarian cancer).

Mucinous cystadenoma is a benign cystic tumor lined by a mucinous epithelium. It is a type of cystic adenoma (cystadenoma).

Mucinous cystadenoma may arise in a number of locations; however, mucinous cystadenoma at different locations are not generally considered to be related to one another.

These tumours are of the following types, characterized by their abnormal production of otherwise apparently normal cells or tissues.

Although each of the cell and tissue types normally occurs in just one sex (male or female), within a tumour they can occur in the opposite sex. Consequently, depending on the specific histology produced, these tumours can cause virilization in women and feminization in men.

Despite their name, germ cell tumors occur both within and outside the ovary and testis.

- head

- inside the cranium — pineal and suprasellar locations are most commonly reported

- inside the mouth — a fairly common location for teratoma

- neck

- mediastinum — account for 1% to 5% of all germ cell neoplasms

- pelvis, particularly sacrococcygeal teratoma

- ovary

- testis

In females, germ cell tumors account for 30% of ovarian tumors, but only 1 to 3% of ovarian cancers in North America. In younger women germ cell tumors are more common, thus in patients under the age of 21, 60% of ovarian tumors are of the germ cell type, and up to one-third are malignant. In males, germ cell tumors of the testis occur typically after puberty and are malignant (testicular cancer). In neonates, infants, and children younger than 4 years, the majority of germ cell tumors are sacrococcygeal teratomas.

Males with Klinefelter syndrome have a 50 times greater risk of germ cell tumors (GSTs). In these persons, GSTs usually contain nonseminomatous elements, present at an earlier age, and seldom are gonadal in location.

An immature teratoma is a rare type of malignant (cancerous) germ cell tumor (type of tumor that begins in the cells that give rise to sperm or eggs).

Like a mature teratoma, it contains several different types of tissue such as hair, muscle, and bone. Unlike a mature teratoma, it contains primitive neuroepithelium.

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

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.

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.

Ovarian cancer is classified according to the histology of the tumor, obtained in a pathology report. Histology dictates many aspects of clinical treatment, management, and prognosis.

- Surface epithelial-stromal tumours, also known as ovarian epithelial tumors, are the most common type of ovarian cancer. It includes serous tumour, endometrioid tumor, and mucinous tumour. They can be benign (cystadenoma) or malignant (cystadenocarcinoma). Less common tumors are malignant Brenner tumor and transitional cell carcinoma of the ovary.

- Sex cord-stromal tumor, including estrogen-producing granulosa cell tumor and virilizing Sertoli-Leydig cell tumor or arrhenoblastoma, accounts for 8% of ovarian cancers.

- Germ cell tumor accounts for approximately 30% of ovarian tumors but only 5% of ovarian cancers, because most germ cell tumors are teratomas and most teratomas are benign. Germ cell tumors tend to occur in young women (20's-30's) and girls. Whilst overall the prognosis of germ cell tumors tend to be favourable, it can vary substantially with specific histology: for instance, the prognosis of the most common germ cell tumor (dysgerminomas) tends to be good, whilst the second most common (endodermal sinus tumor) tends to have a poor prognosis. In addition, the cancer markers used vary with tumor type: choriocarcinomas are monitored with beta-HCG; dysgerminomas with LDH; and endodermal sinus tumors with alpha-fetoprotein.

- Mixed tumors, containing elements of more than one of the above classes of tumor histology.

Serous cystadenomas are diagnosed by histomorphologic examination, by pathologists. Grossly, they are, usually, unilocular cysts that contain clear, straw-coloured fluid. Microscopically, the cyst lining consists of a simple epithelium with cilia that may be columnar or flat.

A struma ovarii (literally: goitre of the ovary) is a rare form of monodermal teratoma that contains mostly thyroid tissue, which may cause hyperthyroidism.

Despite its name, struma ovarii is not restricted to the ovary.

The vast majority of struma ovarii are benign tumors; however, malignant tumors of this type is found in a small percentage of cases.

Due to its classification, a dermoid cyst can occur wherever a teratoma can occur.

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.

Typical signs and symptoms of Wilms tumor include the following:

- a painless, palpable abdominal mass

- loss of appetite

- abdominal pain

- fever

- nausea and vomiting

- blood in the urine (in about 20% of cases)

- high blood pressure in some cases (especially if synchronous or metachronous bilateral kidney involvement)

A dermoid cyst is a teratoma of a cystic nature that contains an array of developmentally mature, solid tissues. It frequently consists of skin, hair follicles, and sweat glands, while other commonly found components include clumps of long hair, pockets of sebum, blood, fat, bone, nails, teeth, eyes, cartilage, and thyroid tissue.

As dermoid cysts grow slowly and contain mature tissue, this type of cystic teratoma is nearly always benign. In those rare cases wherein the dermoid cyst is malignant, a squamous cell carcinoma usually develops in adults, while infants and children usually present with an endodermal sinus tumor.

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