Sertoli cell tumors are known to occur in other species, including domestic ducks, dogs, and horses.

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.

This is a very rare tumor, since only about 1 in 35,000 to 40,000 people have VHL, of whom about 10% have endolymphatic sac tumors. Patients usually present in the 4th to 5th decades without an gender predilection. The tumor involves the endolymphatic sac, a portion of the intraosseous inner ear of the posterior petrous bone.

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.

Although often described as benign, a teratoma does have malignant potential. In a UK study of 351 infants and children diagnosed with "benign" teratoma reported 227 with MT, 124 with IT. Five years after surgery, event-free survival was 92.2% and 85.9%, respectively, and overall survival was 99% and 95.1%. A similar study in Italy reported on 183 infants and children diagnosed with teratoma. At 10 years after surgery, event free and overall survival were 90.4% and 98%, respectively.

Depending on which tissue(s) it contains, a teratoma may secrete a variety of chemicals with systemic effects. Some teratomas secrete the "pregnancy hormone" human chorionic gonadotropin (βhCG), which can be used in clinical practice to monitor the successful treatment or relapse in patients with a known HCG-secreting teratoma. This hormone is not recommended as a diagnostic marker, because most teratomas do not secrete it. Some teratomas secrete thyroxine, in some cases to such a degree that it can lead to clinical hyperthyroidism in the patient. Of special concern is the secretion of alpha-fetoprotein (AFP); under some circumstances AFP can be used as a diagnostic marker specific for the presence of yolk sac cells within the teratoma. These cells can develop into a frankly malignant tumor known as yolk sac tumor or endodermal sinus tumor.

Adequate follow-up requires close observation, involving repeated physical examination, scanning (ultrasound, MRI, or CT), and measurement of AFP and/or βhCG.

The exact cause of Sertoli-Leydig Cell Tumor is not known.

Research studies seem to indicate that certain genetic mutations (in the DICER1 gene) may play a role in many cases.

Testicular microlithiasis is an unusual condition diagnosed on testicular ultrasound. It is found in between 1.5 to 5% of normal males, and may be found in up to 20% of individuals with subfertility. It is an asymptomatic, non-progressive disease. The cause is unknown, but this condition has been associated with testicular cancer in a small group of individuals, cryptorchidism, mumps, infertility and intraepithelial germ cell neoplasia. Classic testicular microlithiasis is defined as five or more echogenic foci per view in either or both testes, and limited testicular microlithiasis defined as one or more echogenic foci that do not satisfy the criteria for classic testicular microlithiasis. In 80% of cases, both testicles are affected.

Testicular microlithiasis is not associated with risk of testicular cancer in asymptomatic individuals with no risk factors for testicular germ cell tumor. However, a large meta-analysis has shown that in individuals with associated risk factors for testicular germ cell tumor, the increase in risk of concurrent diagnosis of testicular germ cell tumor, or testicular carcinoma-in-situ upon biopsy is approximately eight to ten-fold.

There is extensive controversy over whether testicular microlithiasis in individuals with testicular germ cell tumor, or risk factors for such, should undergo testicular biopsy to exclude the presence of testicular carcinoma-in-situ, also known as intratubular germ cell neoplasia of unclassified type. Additionally, whether the presence of testicular microlithiasis should influence decision for adjuvant chemotherapy or surveillance in individuals with testicular germ cell tumor remains unclear. A recent review in Nature Reviews Urology has comprehensively evaluated these topics.

There is no cure or treatment for testicular microlithiasis, however, patients may be monitored via ultrasound to make sure that other conditions do not develop. Emphasis on testicular examination is the recommended follow up for asymptomatic men incidentally identified with testicular microlithiasis. For men with risk factors for testicular germ cell tumor such as subfertility however, individualized discussion with their urologists is necessary.

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 urogenital neoplasm is a tumor of the urogenital system.

Types include:

- Cancer of the breast and female genital organs: (Breast cancer, Vulvar cancer, Vaginal cancer, Cervical cancer, Uterine cancer, Endometrial cancer, Ovarian cancer)

- Cancer of the male genital organs (Carcinoma of the penis, Prostate cancer, Testicular cancer)

- Cancer of the urinary organs (Renal cell carcinoma, Bladder cancer)

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

Due to the difficulty in identifying the tumour using imaging techniques, an orchiectomy is often performed. The majority of sertoli cell tumours are benign, so this is sufficient. There is no documented benefit of chemotherapy or radiotherapy.

The usual treatment is surgery. The surgery usually is a fertility-sparing unilateral salpingo-oophorectomy. For malignant tumours, the surgery may be radical and usually is followed by adjuvant chemotherapy, sometimes by radiation therapy. In all cases, initial treatment is followed by surveillance. Because in many cases Sertoli–Leydig cell tumour does not produce elevated tumour markers, the focus of surveillance is on repeated physical examination and imaging. Given that many cases of Sertoli–Leydig cell tumor of the ovary are hereditary, referral to a clinical genetics service should be considered.

The prognosis is generally good as the tumour tends to grow slowly and usually is benign: 25% are malignant. For malignant tumours with undifferentiated histology, prognosis is poor.

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.

Wide excision is the treatment of choice, although attempting to preserve hearing. Based on the anatomic site, it is difficult to completely remove, and so while there is a good prognosis, recurrences or persistence may be seen. There is no metastatic potential. Patients who succumb to the disease, usually do so because of other tumors within the von Hippel-Lindau complex rather than from this tumor.

The usual chemotherapy regimen has limited efficacy in tumours of this type, although Imatinib has shown some promise. There is no current role for radiotherapy.

The usual treatment is surgery. The surgery for females usually is a fertility-sparing unilateral salpingo-oophorectomy. For malignant tumours, the surgery may be radical and usually is followed by adjuvant chemotherapy, sometimes by radiation therapy. In all cases, initial treatment is followed by surveillance. Because in many cases Leydig cell tumour does not produce elevated tumour markers, the focus of surveillance is on repeated physical examination and imaging.

In males, a radical inguinal orchiectomy is typically performed. However, testes-sparing surgery can be used to maintain fertility in children and young adults. This approach involves an inguinal or scrotal incision and ultrasound guidance if the tumour is non-palpable. This can be done because the tumour is typically unifocal, not associated with precancerous lesions, and is unlikely to recur.

The prognosis is generally good as the tumour tends to grow slowly and usually is benign: 10% are malignant. For malignant tumours with undifferentiated histology, prognosis is poor.

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.

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.

Generally, there is a good prognosis for low-grade tumors, and a poor prognosis for high-grade tumors.

Most cases of polyorchidism are asymptomatic, and are discovered incidentally, in the course of treating another condition. In the majority of cases, the supernumerary testicle is found in the scrotum.

However, polyorchidism can occur in conjunction with cryptorchidism, where the supernumerary testicle is undescended or found elsewhere in the body. These cases are associated with a significant increase in the incidence of testicular cancer: 0.004% for the general population vs 5.7% for a supernumerary testicle not found in the scrotum.

Polyorchidism can also occur in conjunction with infertility, inguinal hernia, testicular torsion, epididymitis, hydrocele testis and varicocele. However, it is not clear whether polyorchidism causes or aggravates these conditions, or whether the existence of these conditions leads sufferers to seek medical attention and thus become diagnosed with a previously undetected supernumerary testicle.

Most treatments involve some combination of surgery and chemotherapy. Treatment with cisplatin, etoposide, and bleomycin has been described.

Before modern chemotherapy, this type of neoplasm was highly lethal, but the prognosis has significantly improved since.

When endodermal sinus tumors are treated promptly with surgery and chemotherapy, fatal outcomes are exceedingly rare.

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.

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.

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.