GCNIS is seen in the following settings:

- Almost all invasive germ cell tumours of the testis in adults

- Fifty percent of patients with GCNIS developed invasive germ cell tumours within five years of initial diagnosis.

- Five percent of contralateral testes in men with a history of prior testicular germ cell tumour.

- Less than five percent of cryptorchid testes.

- Less than one percent of patients with infertility.

The average age of diagnosis is between 15 and 35 years. This is about 5 to 10 years older than men with other germ cell tumors of the testes. In most cases, they produce masses that are readily felt on testicular self-examination; however, in up to 11 percent of cases, there may be no mass able to be felt, or there may be testicular atrophy. Testicular pain is reported in up to one fifth of cases. Low back pain may occur after metastasis to the retroperitoneum.

Some cases of seminoma can present as a primary tumour outside the testis, most commonly in the mediastinum. In the ovary, the tumor is called a dysgerminoma, and in non-gonadal sites, particularly the central nervous system, it is called a germinoma.

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.

Not all germ cell tumors (GCTs) arise from "intratubular germ cell neoplasia". The following testicular GCTs do not arise from ITGCN:

- Spermatocytic seminoma

- Pediatric Yolk sac tumors (endodermal sinus tumour). This is currently an area of controversy as some authors dispute the absence of ITGCN in these cases.

- Teratoma (rare exceptions)

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.

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).

Seminoma (also known as "pure seminoma" or "classical seminoma") is a germ cell tumor of the testicle or, more rarely, the mediastinum or other extra-gonadal locations. It is a malignant neoplasm and is one of the most treatable and curable cancers, with a survival rate above 95% if discovered in early stages.

Testicular seminoma originates in the germinal epithelium of the seminiferous tubules. About half of germ cell tumors of the testicles are seminomas. Treatment usually requires removal of one testicle. However, fertility usually isn't affected. All other sexual functions will remain intact.

In the ovary, embryonal carcinoma is quite rare, amounting to approximately three percent of ovarian germ cell tumours. The median age at diagnosis is 15 years. Symptoms and signs are varied, and may include sexual precocity and abnormal (increased, reduced or absent) uterine bleeding.

There may be elevations in serum human chorionic gonadotropin (hCG) and alpha fetoprotein (AFP) levels but it would be in association with other tumors, (e.g. yolk sac tumor) because they themselves do not produce the serum markers. At surgery, there is extension of the tumour beyond the ovary in forty percent of cases. They are generally large, unilateral tumours, with a median diameter of 17 centimetres. Long-term survival has improved following the advent of chemotherapy. The gross and histologic features of this tumour are similar to that seen in the testis.

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.

In the testis pure embryonal carcinoma is also uncommon, and accounts for approximately ten percent of testicular germ cell tumours. However, it is present as a component of almost ninety percent of mixed nonseminomatous germ cell tumours. The average age at diagnosis is 31 years, and typically presents as a testicular lump which may be painful. One fifth to two thirds of patients with tumours composed predominantly of embryonal carcinoma have metastases at diagnosis.

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

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.

Spermatocytic seminoma is a rare tumour, making up only one to two percent of all testicular germ cell tumours. Men presenting with this tumour are generally 50 to 60 years old, and its occurrence is rare in men under 30 years old. Most present with slow, painless testicular enlargement, which may involve both testes.

Although testicular cancer can be derived from any cell type found in the testicles, more than 95% of testicular cancers are germ cell tumors (GCTs). Most of the remaining 5% are sex cord-gonadal stromal tumours derived from Leydig cells or Sertoli cells. Correct diagnosis is necessary to ensure the most effective and appropriate treatment. To some extent, this can be done via blood tests for tumor markers, but definitive diagnosis requires examination of the histology of a specimen by a pathologist.

Most pathologists use the World Health Organization classification system for testicular tumors:

- Germ cell tumors

- "Precursor lesions"

- Intratubular germ cell neoplasia

- Unclassified type (carcinoma in situ)

- Specified types

- "Tumors of one histologic type (pure forms)"

- Seminoma

- Variant - Seminoma with syncytiotrophoblastic cells

- Spermatocytic seminoma

- Variant - spermatocytic seminoma with sarcoma

- Embryonal carcinoma

- Yolk sac tumor

- Trophoblastic tumors

- Choriocarcinoma

- Variant - monophasic choriocarcinoma

- Placental site trophoblastic tumour

- Cystic trophoblastic tumor

- Teratoma

- Variant - Dermoid cyst

- Variant - Epidermoid cyst

- Variant - Monodermal teratoma (Carcinoid, Primitive neuroectodermal tumor (PNET), Nephroblastoma-like tumor, others.

- Variant - Teratomic with somatic-type malignancy

- "Tumours of more than one histologic type (mixed forms)"

- Embryonal carcinoma and teratoma

- Teratoma and seminoma

- Choriocarcinoma and teratoma.embryonal carcinoma

- Others

- Sex cord/Gonadal stromal tumors

- Leydig cell tumor

- Sertoli cell tumor

- Lipid rich variant

- Scleriosing variant

- Large cell calcifying variant

- Intratubular sertoli cell neoplasia in Peutz-Jeghers syndrome

- Granulosa cell tumor

- Adult type

- Juvenile type

- Thecoma Fibroma Group

- Thecoma

- Fibroma

- Sex cord/gonadal stromal tumor - incompletely differentiated

- Sex cord/gonadal stromal tumor - mixed types

- Mixed Germ Cell and Sex Cord/Gonadal Stromal Tumors

- Gonadoblastoma

- Germ cell-sex cord/gonadal stromal tumor, unclassified

- Miscellaneous tumours of the testis

- Carcinoid

- Tumors of ovarian epithelial types

- Serous tumor of borderline malignancy

- Serous carcinoma

- Well differentiated endometrioid tumor

- Mucinous cystadenoma

- Mucinous cystadenocarcinoma

- Brenner tumor

- Nephroblastoma

- Paraganglioma

- Haematopoietic tumors

- Tumours of collecting ducts and rete

- Adenoma

- Carcinoma

- Tumors of the paratesticular structures

- Adenomatoid tumor

- Malignant and Benign Mesothelioma

- Adenocarcinoma of the epididymis

- Papillary cystadenoma of the epididymis

- Melanotic neuroectodermal tumor

- Desmoplastic small round cell tumor

- Mesenchymal tumors of the spermatic cord and testicular adnexae

- Lipoma

- Liposarcoma

- Rhabdomyosarcoma

- Aggressive angiomyxoma

- Angiomyofibroblastoma-like tumor (see Myxoma)

- Fibromatosis

- Fibroma

- Solitary fibrous tumor

- Others

- Secondary tumors of the testis

Early signs and symptoms of ovarian cancer may be absent or subtle. In most cases, symptoms exist for several months before being recognized and diagnosed. Symptoms can be misdiagnosed as irritable bowel syndrome. The early stages of ovarian cancer tend to be painless. Symptoms can vary based on the subtype. Low malignant potential (LMP) tumors, also known as borderline tumors, do not cause an increase in CA125 levels and are not identifiable with an ultrasound. The typical symptoms of an LMP tumor can include abdominal distension or pelvic pain. Particularly large masses tend to be benign or borderline.

The most typical symptoms of ovarian cancer include bloating, abdominal or pelvic pain or discomfort, back pain, irregular menstruation or postmenopausal vaginal bleeding, pain or bleeding after or during sexual intercourse, loss of appetite, fatigue, diarrhea, indigestion, heartburn, constipation, nausea, feeling full, and possibly urinary symptoms (including frequent urination and urgent urination).

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.

Unlike benign germ cell tumors of the mediastinum, malignant mediastinal tumors are usually symptomatic at the time of diagnosis. Most mediastinal malignant tumors are large and cause symptoms by compressing or invading adjacent structures, including the lungs, pleura, pericardium, and chest wall.

Seminomas grow relatively slowly and can become very large before causing symptoms. Tumors 20 to 30 cm in diameter can exist with minimal symptomatology.

One of the first signs of testicular cancer is often a lump or swelling in the testes. The U.S. Preventive Services Task Force (USPSTF) recommends against routine screening for testicular cancer in asymptomatic adolescent and adults including routine testicular self-exams. However, the American Cancer Society suggests that some men should examine their testicles monthly, especially if they have a family history of cancer, and the American Urological Association recommends monthly testicular self-examinations for all young men.

Symptoms may also include one or more of the following:

- a lump in one testis which may or may not be painful

- sharp pain or a dull ache in the lower abdomen or scrotum

- a feeling often described as "heaviness" in the scrotum

- breast enlargement (gynecomastia) from hormonal effects of β-hCG

- low back pain (lumbago) due to the cancer spreading to the lymph nodes along the back

It is not very common for testicular cancer to spread to other organs, apart from the lungs. If it has, however, the following symptoms may be present:

- shortness of breath (dyspnea), cough or coughing up blood (hemoptysis) from metastatic spread to the lungs

- a lump in the neck due to metastases to the lymph nodes

Testicular cancer, cryptorchidism, hypospadias, and poor semen quality make up the syndrome known as testicular dysgenesis syndrome.

Spermatocytic seminoma is a neoplasm of the testis ("i.e." a tumour of the testis), and classified as a germ cell tumour.

The name of the tumour comes from the similarity (under the microscope) between the small cells of the tumour and secondary spermatocytes.

Choriocarcinoma is a malignant, trophoblastic cancer, usually of the placenta. It is characterized by "early hematogenous spread" to the lungs. It belongs to the malignant end of the spectrum in gestational trophoblastic disease (GTD). It is also classified as a germ cell tumor and may arise in the testis or ovary.

The growing mass may cause pain if ovarian torsion develops. Symptoms can be caused by a mass pressing on the other abdominopelvic organs or from metastases. If these symptoms start to occur more often or more severely than usual, especially after no significant history of such symptoms, ovarian cancer is considered. Metastases may cause a Sister Mary Joseph nodule. Rarely, teratomas can cause growing teratoma syndrome or peritoneal gliomatosis. Some experience menometrorrhagia and abnormal vaginal bleeding after menopause in most cases. Other common symptoms include hirsutism, abdominal pain, virilization, and an adnexal mass.

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.

Mediastinal germ cell tumors are tumors that derive from germ cell rest remnants in the mediastinum. They most commonly occur in the gonad but occasionally elsewhere.

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.

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.