A prospective study of ovarian sex cord–stromal tumours in children and adolescents began enrolling participants in 2005.

Spermatocytic seminomas are not considered a subtype of seminoma and unlike other germ cell tumours do not arise from intratubular germ cell neoplasia.

The 1997 International Germ Cell Consensus Classification is a tool for estimating the risk of relapse after treatment of malignant germ cell tumor.

A small study of ovarian tumors in girls reports a correlation between cystic and benign tumors and, conversely, solid and malignant tumors. Because the cystic extent of a tumor can be estimated by ultrasound, MRI, or CT scan before surgery, this permits selection of the most appropriate surgical plan to minimize risk of spillage of a malignant tumor.

Access to appropriate treatment has a large effect on outcome. A 1993 study of outcomes in Scotland found that for 454 men with non-seminomatous (non-germinomatous) germ cell tumors diagnosed between 1975 and 1989, 5-year survival increased over time and with earlier diagnosis. Adjusting for these and other factors, survival was 60% higher for men treated in a cancer unit that treated the majority of these men, even though the unit treated more men with the worst prognosis.

Choriocarcinoma of the testicles has the worst prognosis of all germ cell cancers

A retrospective study of 83 women with sex cord–stromal tumours (73 with granulosa cell tumour and 10 with Sertoli-Leydig cell tumour), all diagnosed between 1975 and 2003, reported that survival was higher with age under 50, smaller tumour size, and absence of residual disease. The study found no effect of chemotherapy. A retrospective study of 67 children and adolescents reported some benefit of cisplatin-based chemotherapy.

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.

Since gestational choriocarcinoma (which arises from a hydatidiform mole) contains paternal DNA (and thus paternal antigens), it is exquisitely sensitive to chemotherapy. The cure rate, even for metastatic gestational choriocarcinoma, is around 90–95%.

At present, treatment with single-agent methotrexate is recommended for low-risk disease, while intense combination regimens including EMACO (etoposide, methotrexate, actinomycin D, cyclosphosphamide and vincristine (Oncovin) are recommended for intermediate or high-risk disease.

Hysterectomy (surgical removal of the uterus) can also be offered to patients > 40 years of age or those for whom sterilisation is not an obstacle. It may be required for those with severe infection and uncontrolled bleeding.

Choriocarcinoma arising in the testicle is rare, malignant and highly resistant to chemotherapy. The same is true of choriocarcinoma arising in the ovary. Testicular choriocarcinoma has the worst prognosis of all germ-cell cancers.

A major risk factor for the development of testis cancer is cryptorchidism (undescended testicles). It is generally believed that the presence of a tumor contributes to cryptorchidism; when cryptorchidism occurs in conjunction with a tumor then the tumor tends to be large. Other risk factors include inguinal hernias, Klinefelter syndrome, and mumps orchitis. Physical activity is associated with decreased risk and sedentary lifestyle is associated with increased risk. Early onset of male characteristics is associated with increased risk. These may reflect endogenous or environmental hormones.

Higher rates of testicular cancer in Western nations have been linked to the use of cannabis.

Some investigators suggest that this distribution arises as a consequence of abnormal migration of germ cells during embryogenesis. Others hypothesize a widespread distribution of germ cells to multiple sites during normal embryogenesis, with these cells conveying genetic information or providing regulatory functions at somatic sites.

Extragonadal germ cell tumors were thought initially to be isolated metastases from an undetected primary tumor in a gonad, but it is now known that many germ cell tumors are congenital and originate outside the gonads. The most notable of these is sacrococcygeal teratoma, the single most common tumor diagnosed in babies at birth.

Of all anterior mediastinal tumors, 15–20% are germ cell tumors of which approximately 50% are benign teratomas.

Choriocarcinoma of the placenta during pregnancy is preceded by:

- hydatidiform mole (50% of cases)

- spontaneous abortion (20% of cases)

- ectopic pregnancy (2% of cases)

- normal term pregnancy (20–30% of cases)

- hyperemesis gravidarum

Rarely, choriocarcinoma occurs in primary locations other than the placenta; very rarely, it occurs in testicles. Although trophoblastic components are common components of mixed germ cell tumors, pure choriocarcinoma of the adult testis is rare. Pure choriocarcinoma of the testis represents the most aggressive pathologic variant of germ cell tumors in adults, characteristically with early hematogenous and lymphatic metastatic spread. Because of early spread and inherent resistance to anticancer drugs, patients have poor prognosis. Elements of choriocarcinoma in a mixed testicular tumor have no prognostic importance.

Choriocarcinomas can also occur in the ovaries.

Spermatocytic seminoma is not considered a subtype of seminoma and, unlike seminoma and most other germ cell tumours, it does not arise from "intratubular germ cell neoplasia". It has not been described as arising in locations outside the testis, and does not occur in association with other germ cell tumours.

The new WHO classification, due to be published in 2016, will rename the condition spermatocytic tumour to avoid confusion with classical seminoma as the biology and treatment are different.

Most testicular germ cell tumors have too many chromosomes, and most often they are triploid to tetraploid. An isochromosome 12p (the short arm of chromosome 12 on both sides of the same centromere) is present in about 80% of the testicular cancers, and also the other cancers usually have extra material from this chromosome arm through other mechanisms of genomic amplification.

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.

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.

Dysgerminomas, like other seminomatous germ cell tumors, are very sensitive to both chemotherapy and radiotherapy. For this reason, with treatment patients' chances of long-term survival, even cure, is excellent.

Trophoblastic neoplasms are neoplasms which derive from trophoblastic tissue.

Examples include:

- choriocarcinoma

- hydatidiform mole

Embryonal carcinoma is a relatively uncommon type of germ cell tumour that occurs in the ovaries and testes.

The risk of a repeat GTD is approximately 1 in 100, compared with approximately 1 in 1000 risk in the general population. Especially women whose hCG levels remain significantly elevated are at risk of developing a repeat GTD.

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.

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".

Embryonal teratomas most commonly occur in the sacrococcygeal region: sacrococcygeal teratoma is the single most common tumor found in newly born humans.

Of teratomas on the skull sutures, approximately 50% are found in or adjacent to the orbit. Limbal dermoid is a choristoma, not a teratoma.

Teratoma qualifies as a rare disease, but is not extremely rare. Sacrococcygeal teratoma alone is diagnosed at birth in one out of 40,000 humans. Given the current human population and birth-rate, this equals five per day or 1800 per year. Add to that number sacrococcygeal teratomas diagnosed later in life, and teratomas in other locales, and the incidence approaches ten thousand new diagnoses of teratoma per year.

The World Health Organisation classification of testicular tumours subdivides ITGCN into (1) a more common, unspecified type (ITGCNU), and (2) other specific subtypes. The most common specific subtypes are intratubular embryonal carcinoma and intratubular seminoma.

Germ cell neoplasia in situ, abbreviated GCNIS, represents the precursor lesion for many types of testicular germ cell tumors. As the name suggests, it represents a neoplastic process of germ cells that is confined to the spermatogonial niche.

The term GCNIS was introduced with the 2016 edition of the WHO classification of urological tumours. It replaces the previous term intratubular germ cell neoplasia, abbreviated ITGCN or IGCN and also known as testicular intratubular germ cell neoplasia and intratubular germ cell neoplasia of the testis. GCNIS more accurate describes the lesion as it arises between the basement membrane and Sertoli cells (the cells that 'nurse' the developing germ cell). The common, unspecified variant of the entity was once considered to be a carcinoma in situ although the term "carcinoma "in situ"" is now largely historical as it is not an accurate description of the process.

Giant-cell lung cancers have long been considered to be exceptionally aggressive malignancies that grow very rapidly and have a very poor prognosis.

Many small series have suggested that the prognosis of lung tumors with giant cells is worse than that of most other forms of non-small-cell lung cancer (NSCLC), including squamous cell carcinoma, and spindle cell carcinoma.

The overall five-year survival rate in GCCL varies between studies but is generally considered to be very low. The (US) Armed Forces Institute of Pathology has reported a figure of 10%, and in a study examining over 150,000 lung cancer cases, a figure of 11.8% was given. However, in the latter report the 11.8% figure was based on data that included spindle cell carcinoma, a variant which is generally considered to have a less dismal prognosis than GCCL. Therefore, the likely survival of "pure" GCCL is probably lower than the stated figure.

In the large 1995 database review by Travis and colleagues, giant-cell carcinoma has the third-worst prognosis among 18 histological forms of lung cancer. (Only small-cell carcinoma and large-cell carcinoma had shorter average survival.)

Most GCCL have already grown and invaded locally and/or regionally, and/or have already metastasized distantly, and are inoperable, at the time of diagnosis.

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.

Adenomatoid tumor is a benign mesothelial tumor, which arises from the lining of organs. It generally presents in the genital tract, in regions such as the testis and epididymis. It is the second most common extratesticular scrotal mass, after lipoma, and accounts for 30% of these masses. It also has been found in the pancreas.

In the female, it has been found in the body of the uterus and the fallopian tube.