Although metastasis is widely accepted to be the result of the tumor cells migration, there is a hypothesis saying that some metastases are the result of inflammatory processes by abnormal immune cells. The existence of metastatic cancers in the absence of primary tumors also suggests that metastasis is not always caused by malignant cells that leave primary tumors.

Treatment for brain metastases is primarily palliative, with the goals of therapy being reduction of symptoms and prolongation of life. However, in some patients, particularly younger, healthier patients, aggressive therapy consisting of open craniotomy with maximal excision, chemotherapy, and radiosurgical intervention (Gamma Knife therapy) may be attempted.

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.

Symptomatic care should be given to all patients with brain metastases, as they often cause severe, debilitating symptoms. Treatment consists mainly of:

- Corticosteroids – Corticosteroid therapy is essential for all patients with brain metastases, as it prevents development of cerebral edema, as well as treating other neurological symptoms such as headaches, cognitive dysfunction, and emesis. Dexamethasone is the corticosteroid of choice. Although neurological symptoms may improve within 24 to 72 hours of starting corticosteroids, cerebral edema may not improve for up to a week. In addition, patients may experience adverse side effects from these drugs, such as myopathy and opportunistic infections, which can be alleviated by decreasing the dose.

- Anticonvulsants – Anticonvulsants should be used for patients with brain metastases who experience seizures, as there is a risk of status epilepticus and death. Newer generation anticonvulsants including Lamotrigine and Topiramate are recommended due to their relatively limited side effects. It is not recommended to prophylactically give anti-seizure medications when a seizure has not yet been experienced by a patient with brain metastasis.

Most people with cancer of unknown primary origin have widely disseminated and incurable disease, although a few can be cured through treatment. With treatment, typical survival with CUP ranges from 6 to 16 months. Survival rates are lower in cases with visceral metastatic disease, ranging from 6 to 9 months. Survival rates are higher when the cancer is more limited to lymph nodes, pleura, or peritoneal metastasis, which ranges from 14 to 16 months. Long-term prognosis is somewhat better if a particular source of cancer is strongly suggested by clinical evidence.

The most successful treatment for angiosarcoma is amputation of the affected limb if possible. Chemotherapy may be administered if there is metastatic disease. If there is no evidence of metastasis beyond the lymphedematous limb, adjuvant chemotherapy may be given anyway due to the possibility of micrometastatic disease. Evidence supporting the effectiveness of chemotherapy is, in many cases, unclear due to a wide variety of prognostic factors and small sample size. However, there is some evidence to suggest that drugs such as paclitaxel, doxorubicin, ifosfamide, and gemcitabine exhibit antitumor activity.

CUP sometimes runs in families. It has been associated with familial lung, kidney, and colorectal cancers, which suggests that these sites may often be the origin of unidentifiable CUP cancers.

Some patients with metastatic breast cancer opt to try alternative therapies such as vitamin therapy, homeopathic treatments, a macrobiotic diet, chiropractic or acupuncture. There is no evidence that any of these therapies are effective; they may be harmful, either because patients pass up effective conventional therapies such as chemotherapy or anti-estrogen therapy in favor of alternative treatments, or because the treatments themselves are harmful (as in the case of apricot-pit therapy—which exposes the patient to cyanide—or in chiropractic, which can be dangerous to patients with cancer metastatic to the spinal bones or spinal cord. A macrobiotic diet is neither effective nor safe as it could hypothetically induce weight loss due to severe dietary restriction. There is limited evidence that acupuncture might relive pain in cancer patients, but data so far is insufficient to recommend its use outside of clinical trials.

There is free peer support and an online platform to interact with others going through various therapies, including Abraxane.

Treatment of metastatic breast cancer is currently an active area of research. Several medications are in development or in phase I/II trials. Typically new medications and treatments are first tested in metastatic cancer before trials in primary cancer are attempted.

Another area of research is finding combination treatments which provide higher efficacy with reduced toxicity and side effects.

Experimental medications:

- sorafenib a combined Tyrosine protein kinases inhibitor.

Complete radical surgical resection is the treatment of choice for EMECL, and in most cases, results in long-term survival or cure.

Micrometastasis is a form of metastasis (the spread of a cancer from its original location to other sites in the body) in which the newly formed tumors are too minuscule to be detected.

Adjuvant chemotherapy and adjuvant radiotherapy are directed at killing any micrometastases, thus preventing relapse (regrowth of the cancer) and the (likely) death of the patient. Early detection of micrometastases could identify the patients who are most (and least) likely to benefit from adjuvant therapy.

Treatment consists of surgical excision (the extent of which ranges from tumor excision to limb amputation, depending on the tumor) and in almost all cases radiation. Radiation eliminates the need for limb amputation and there is level I evidence to show that it leads to equivalent rates of survival (Rosenberg et al. NCI Canada). Radiation may be delivered either pre-op or post-op depending on surgeon and multidisciplinary tumor board's recommendations. Radiation can be omitted for low grade, Stage I excised tumors with >1 cm margin (NCCN). Chemotherapy remains controversial in MFH.

The usual site of metastatic disease is the lungs, and metastases should be resected if possible. Unresectable or inoperable lung metastasis may be treated with stereotactic body radiation therapy (SBRT) with excellent local control. However, neither surgery nor SBRT will prevent emergence of additional metastasis elsewhere in the lung. Therefore, role of chemotherapy needs to be further explored to address systemic metastasis.

Prognosis depends on the primary tumor grade (appearance under the microscope as judged by a pathologist), size, resectability (whether it can be completely removed surgically), and presence of metastases. The five-year survival is 80%.

The specific treatment will depend on the tumor's type, location, size, and whether the cancer has spread to other organs. Surgical removal of the tumor remains the standard treatment of choice, but additional forms of therapy such as radiation therapy, chemotherapy, or immunotherapy exist.

When detected early, skin cancer in cats and dogs can often be treated successfully. In many cases, a biopsy can remove the whole tumor, as long as the healthy tissues removed from just outside the tumor area do not contain any cancer cells.

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.

Mammary tumors are the third most common neoplasia in cats, following lymphoid and skin cancers. The incidence of mammary tumors in cats is reduced by 91 percent in cats spayed prior to six months of age and by 86 percent in cats spayed prior to one year, according to one study. Siamese cats and Japanese breeds seem to have increased risk, and obesity also appears to be a factor in tumor development. Malignant tumors make up 80 to 96 percent of mammary tumors in cats, almost all adenocarcinomas. Male cats may also develop mammary adenocarcinoma, albeit rarely, and the clinical course is similar to female cats. As in dogs, tumor size is an important prognostic factor, although for tumors less than three centimeters the individual size is less predictive. According to one study, cats with tumors less than three cm had an average survival time of 21 months, and cats with tumors greater than three cm had an average survival of 12 months. About 10 percent of cat mammary tumors have estrogen receptors, so spaying at the time of surgery has little effect on recurrence or survival time. Metastasis tends to be to the lungs and lymph nodes, and rarely to bone. Diagnosis and treatment is similar to the dog. There is a better prognosis with bilateral radical surgery (removing the both mammary chains) than with more conservative surgery. Doxorubicin has shown some promise in treatment.

Giant-cell tumor (GCT) of the pelvis is uncommon, accounting for only 1.5 to 6% of cases of GCT. In pelvis ilium is the most common site of involvement; ischium and pubis are less frequently involved. It typically presents in adults between age of 20 to 50 with localized swelling and pain. Females are slightly more affected than males.

Average size of the tumor in this region is 9.5 cm.

There are different modalities of treatment of pelvic GCT. Radiotherapy has high rate of recurrence (44%) and risk of soft tissue sarcomas (12%). Thus treatment should be essentially surgical which includes surgical excision. Excision can be extralesional which achieves 90% local tumor control but poor functional outcome or it can be intralesional which has 90% local recurrence rate with good functional outcome.

Massive GCT of pelvis, which is static, not amenable to excision and presenting with mechanical symptoms, can be managed by de-bulking the portion of tumor responsible for mechanical symptoms. And patients need to be followed for local invasion or metastasis.

Dr. Sidney Farber, founder of Dana-Farber Cancer Institute, and his colleagues achieved the first remissions in Wilms tumor in the 1950s. By employing the antibiotic actinomycin D in addition to surgery and radiation therapy, they boosted cure rates from 40 to 89 percent.

Since Krukenberg tumors are secondary (metastatic), management might logically be driven by identifying and treating the primary cancer. The optimal treatment of Krukenberg tumors is unclear. The role of surgical resection has not been adequately addressed but if metastasis is limited to the ovaries, surgery may improve survival. The role of chemotherapy and/or radiotherapy is uncertain but may sometimes be beneficial.

The primary treatment is surgical. FIGO-cancer staging is done at the time of surgery which consists of peritoneal cytology, total hysterectomy, bilateral salpingo-oophorectomy, pelvic/para-aortic lymphadenectomy, and omentectomy. The tumor is aggressive and spreads quickly into the myometrium and the lymphatic system. Thus even in presumed early stages, lymphadenectomy and omentectomy should be included in the surgical approach. If the tumor has spread surgery is cytoreductive followed by radiation therapy and/or chemotherapy.

In a study to determine if adjuvant therapy should be used in patients with stage I UPSC who had undergone surgery, no increased survival was seen when radiation therapy was added versus observation, while the postsurgical treatment with chemotherapy may be beneficial but more data are needed.

A study of the usefulness of platinum-based chemotherapy as an adjuvant after surgery of stage I patients showed that patients with stage 1A who had no residual disease in the hysterectomy specimen had no recurrence regardless if chemotherapy was used or not, however, patients with stage 1A disease with residual disease in the hysterectomy specimen had no recurrence with platinum-based therapy, but those who had no such chemotherapy showed recurrence in 43%. Similarly, patients with stage 1B disease with chemotherapy had no recurrence, while those without chemotherapy had a high degree (77%) of recurrence.

Most mammary tumors in rats are benign fibroadenomas, which are also the most common tumor in the rat. Less than 10 percent are adenocarcinomas. They occur in male and female rats. The tumors can be large and occur anywhere on the trunk. There is a good prognosis with surgery. Spayed rats have a decreased risk of developing mammary tumors.

Treatment depends upon the site and the extent of the disease. Clear cell sarcoma is usually treated with surgery in the first place in order to remove the tumor. The surgical procedure is then followed by radiation and sometimes chemotherapy. Few cases of clear cell sarcoma respond to chemotherapy. Several types of targeted therapy that may be of benefit to clear cell sarcoma patients are currently under investigation.

Induction chemotherapy is the treatment adapted for shrinking the tonsil tumor. It is given prior to other treatments, hence, the term induction. After the therapy is completed, the patient is asked to rest and is evaluated over a period of time. Then the patient is given chemo-radiation therapy (a combination of chemotherapy and radiation) to completely destroy the tumor cells.

The treatment for tonsil carcinoma includes the following methods:

Treatment is primarily surgical, with chemotherapy and radiation therapy sometimes used.

The NCCN guideline recommends CCPDMA or Mohs surgery for the best cure rate of DFSP. Mohs surgery can be extremely effective. It will remove the tumor and all related pathological cells without a wide-area excision that may overlook sarcoma cells that have penetrated muscle tissue.

The standard of care for patients with DFSP is surgery. Usually, complete surgical resection with margins of 2 to 4 cm (recommended) is performed. The addition of adjuvant radiotherapy (irradiation) improves local control in patients with close or positive margins during the surgery. A special surgical technique, the "Mohs micrographic surgery" (MMS), can be employed in patients with DFSP. MMS is technically possible if the DFSP is in an anatomically confined area. A high probability of cure of DFSP can be attained with MMS as long as the final margins are negative. Patients who have a recurrent DFSP can have further surgery, but the probability of adverse effects of surgery and/or metastasis is increased in these patients. The Mohs surgery is highly successful.

Imatinib is approved for treatment. As is true for all medicinal drugs that have a name that ends in "ib," imatinib is a small molecular pathway inhibitor; imatinib inhibits tyrosine kinase. It may be able to induce tumor regression in patients with recurrent DFSP, unresectable DFSP or metastatic DFSP. There is clinical evidence that imatinib, which inhibits PDGF-receptors, may be effective for tumors positive for the t(17;22) translocation.