GCNIS is generally treated by radiation therapy and/or orchiectomy. Chemotherapy used for metastatic germ cell tumours may also eradicate GCNIS.

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.

Women with benign germ cell tumors such as mature teratomas (dermoid cysts) are cured by ovarian cystectomy or oophorectomy. In general, all patients with malignant germ cell tumors will have the same staging surgery that is done for epithelial ovarian cancer. If the patient is in her reproductive years, an alternative is unilateral salpingoophorectomy, while the uterus, the ovary, and the fallopian tube on the opposite side can be left behind. This isn't an option when the cancer is in both ovaries. If the patient has finished having children, the surgery involves complete staging including salpingoophorectomy on both sides as well as hysterectomy.

Most patients with germ cell cancer will need to be treated with combination chemotherapy for at least 3 cycles. The chemotherapy regimen most commonly used in germ cell tumors is called PEB (or BEP), and consists of bleomycin, etoposide, a platinum-based antineoplastic (cisplatin).

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.

The three basic types of treatment are surgery, radiation therapy, and chemotherapy.

Surgery is performed by urologists; radiation therapy is administered by radiation oncologists; and chemotherapy is the work of medical oncologists. In most patients with testicular cancer, the disease is cured readily with minimal long-term morbidity. While treatment success depends on the stage, the average survival rate after five years is around 95%, and stage 1 cancers cases, if monitored properly, have essentially a 100% survival rate.

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

Radiation may be used to treat stage II seminoma cancers, or as adjuvant (preventative) therapy in the case of stage I seminomas, to minimize the likelihood that tiny, non-detectable tumors exist and will spread (in the inguinal and para-aortic lymph nodes). Radiation is ineffective against and is therefore never used as a primary therapy for nonseminoma.

Unlike classical seminoma, spermatocytic seminomas rarely metastasise, so radical orchidectomy alone is sufficient treatment, and retroperitoneal lymph node dissection and adjuvant chemotherapy or radiotherapy are generally not required.

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

Pure mediastinal seminomas are curable in the large majority of patients, even when metastatic at the time of diagnosis. These tumors are highly sensitive to radiation therapy and to combination chemotherapy. However, the cardiotoxicity of mediastinal radiation is substantial and the standard treatment of mediastinal seminomas is with chemotherapy using bleomycin, etoposide and cisplatin for either three or four 21-day treatment cycles depending on the location of any metastatic disease.

Patients with small tumors (usually asymptomatic) that appear resectable usually undergo thoracotomy and attempted complete resection followed by chemotherapy.

The treatment for mediastinal nonseminomatous germ cell tumors should follow guidelines for poor-prognosis testicular cancer. Initial treatment with four courses of bleomycin, etoposide, and cisplatin, followed by surgical resection of any residual disease, is considered standard therapy.

Germinomas, like several other types of germ cell tumor, are sensitive to both chemotherapy and radiotherapy. For this reason, treatment with these methods can offer excellent chances of longterm survival, even cure.

Although chemotherapy can shrink germinomas, it is not generally recommended alone unless there are contraindications to radiation. In a study in the early 1990s, carboplatinum, etoposide and bleomycin were given to 45 germinoma patients, and about half the patients relapsed. Most of these relapsed patients were then recovered with radiation or additional chemotherapy.

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.

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.

For malignant teratomas, usually, surgery is followed by chemotherapy.

Teratomas that are in surgically inaccessible locations, or are very complex, or are likely to be malignant (due to late discovery and/or treatment) sometimes are treated first with chemotherapy.

Treatment is always necessary.

The treatment for hydatidiform mole consists of the evacuation of pregnancy. Evacuation will lead to the relief of symptoms, and also prevent later complications. Suction curettage is the preferred method of evacuation. Hysterectomy is an alternative if no further pregnancies are wished for by the female patient. Hydatidiform mole also has successfully been treated with systemic (intravenous) methotrexate.

The treatment for invasive mole or choriocarcinoma generally is the same. Both are usually treated with chemotherapy. Methotrexate and dactinomycin are among the chemotherapy drugs used in GTD. Only a few women with GTD suffer from poor prognosis metastatic gestational trophoblastic disease. Their treatment usually includes chemotherapy. Radiotherapy can also be given to places where the cancer has spread, e.g. the brain.

Women who undergo chemotherapy are advised not to conceive for one year after completion of treatment. These women also are likely to have an earlier menopause. It has been estimated by the Royal College of Obstetricians and Gynaecologists that the age at menopause for women who receive single agent chemotherapy is advanced by 1 year, and by 3 years for women who receive multi agent chemotherapy.

Intratesticular masses that appear suspicious on an ultrasound should be treated with an inguinal orchiectomy. The pathology of the removed testicle and spermatic cord indicate the presence of the seminoma and assist in the staging. Tumors with both seminoma and nonseminoma elements or that occur with the presence of AFP should be treated as nonseminomas. Abdominal CT or MRI scans as well as chest imaging are done to detect for metastasis. The analysis of tumor markers also helps in staging.

The preferred treatment for most forms of stage 1 seminoma is active surveillance. Stage 1 seminoma is characterized by the absence of clinical evidence of metastasis. Active surveillance consists of periodic history and physical examinations, tumor marker analysis, and radiographic imaging. Around 85-95% of these cases will require no further treatment. Modern radiotherapy techniques as well as one or two cycles of single-agent carboplatin have been shown to reduce the risk of relapse, but carry the potential of causing delayed side effects. Regardless of treatment strategy, stage 1 seminoma has nearly a 100% cure rate.

Stage 2 seminoma is indicated by the presence of retroperitoneal metastasis. Cases require radiotherapy or, in advanced cases, combination chemotherapy. Large residual masses found after chemotherapy may require surgical resection. Second-line treatment is the same as for nonseminomas.

Stage 3 seminoma is characterized by the presence of metastasis outside the retroperitoneum—the lungs in "good risk" cases or elsewhere in "intermediate risk" cases. This is treated with combination chemotherapy. Second-line treatment follows nonseminoma protocols.

The treatment of choice is complete surgical removal ("i.e.," complete resection). Teratomas are normally well-encapsulated and non-invasive of surrounding tissues, hence they are relatively easy to resect from surrounding tissues. Exceptions include teratomas in the brain, and very large, complex teratomas that have pushed into and become interlaced with adjacent muscles and other structures.

Prevention of recurrence does not require "en bloc" resection of surrounding tissues.

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.

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 uterine curettage is generally done under the effect of anesthesia, preferably spinal anesthesia in hemodynamically stable patients. The advantages of spinal anesthesia over general anesthesia include ease of technique, favorable effects on the pulmonary system, safety in patients with hyperthyroidism and non-tocolytic pharmacological properties. Additionally, by maintaining patient’s consciousness one can diagnose the complications like uterine perforation, cardiopulmonary distress and thyroid storm at an earlier stage than when the patient is sedated or is under general anesthesia.

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

Hydatidiform moles should be treated by evacuating the uterus by uterine suction or by surgical curettage as soon as possible after diagnosis, in order to avoid the risks of choriocarcinoma. Patients are followed up until their serum human chorionic gonadotrophin (hCG) level has fallen to an undetectable level. Invasive or metastatic moles (cancer) may require chemotherapy and often respond well to methotrexate. As they contain paternal antigens, the response to treatment is nearly 100%. Patients are advised not to conceive for half a year after hCG levels have normalized. The chances of having another molar pregnancy are approximately 1%.

Management is more complicated when the mole occurs together with one or more normal fetuses.

The term «persistent trophoblastic disease» (PTD) is used when after treatment of a molar pregnancy, some molar tissue is left behind and again starts growing into a tumour. Although PTD can spread within the body like a malignant cancer, the overall cure rate is nearly 100%.

In the vast majority of patients, treatment of PTD consist of chemotherapy. Only about 10% of patients with PTD can be treated successfully with a second curettage.

Because polyorchidism is very uncommon, there is no standard treatment for the condition. Prior to advances in ultrasound technology, it was common practice to remove the supernumerary testicle. Several cases have been described where routine follow-up examinations conducted over a period of years showed that the supernumerary testicle was stable.

A meta-analysis in 2009 suggested removing non-scrotal supernumerary testicles because of the increased risk of cancer, and regular follow-up in the remaining cases to ensure that the supernumerary testicle remains stable.

Treatment and survival is determined, to a great extent, by whether or not a cancer remains localized or spreads to other locations in the body. If the cancer metastasizes to other tissues or organs it usually dramatically increases a patient's likelihood of death. Some cancers—such as some forms of leukemia, a cancer of the blood, or malignancies in the brain—can kill without spreading at all.

Once a cancer has metastasized it may still be treated with radiosurgery, chemotherapy, radiation therapy, biological therapy, hormone therapy, surgery, or a combination of these interventions ("multimodal therapy"). The choice of treatment depends on a large number of factors, including the type of primary cancer, the size and location of the metastases, the patient's age and general health, and the types of treatments used previously. In patients diagnosed with CUP it is often still possible to treat the disease even when the primary tumor cannot be located.

Current treatments are rarely able to cure metastatic cancer though some tumors, such as testicular cancer and thyroid cancer, are usually curable.

Palliative care, care aimed at improving the quality of life of people with major illness, has been recommended as part of management programs for metastasis.