Radiotherapy is commonly used to treat Merkel-cell cancers. The radiotherapy fields used are usually very large so as to cover sufficient areas of skin. This is necessary because of MCC's aggressive local and regional metastatic behavior.

Adjuvant radiotherapy has been shown to be effective in reducing the rates of recurrence and in increasing the survival of patients with MCC. Patients who present with no distant metastases and a negative sentinel lymph node biopsy have a very good prognosis when treated with both surgery and radiotherapy (approximately 90% survival rate at five years).

Metastatic MCC may respond to treatment with chemotherapy and/or radiation, but current multimodal therapies are usually not curative. Intensive treatment can be effective in shrinking the tumor and improving operability when tumors are too large to be removed or located in a place where removal would be difficult or dangerous, or in palliation of signs and symptoms caused by metastatic 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.

Epithelioid sarcoma (especially advanced stage, recurrent, or metastasized disease) has been shown to be resistant to traditional cancer therapies, necessitating further exploration of novel treatment methods and techniques. Because of the relatively poor response of epithelioid sarcoma to traditional cancer treatments (surgery, chemotherapy, and radiation), new treatment strategies are being looked to.

The U.S. Food and Drug Administration granted in March 2017 an accelerated approval to the checkpoint-inhibitor avelumab for the treatment of adults and pediatric patients 12 years and older with metastatic Merkel cell carcinoma (MCC). This is the first FDA-approved treatment for metastatic MCC. Avelumab targets the PD-1/PD-L1 pathway (proteins found on the body’s immune cells and some cancer cells). By blocking these interactions, avelumab may help the body’s immune system attack cancer cells.

Various chemotherapy agents, including temozolomide, dacarbazine (also termed DTIC), immunotherapy (with interleukin-2 (IL-2) or interferon (IFN)), as well as local perfusion, are used by different centers. The overall success in metastatic melanoma is quite limited.

IL-2 (Proleukin) was the first new therapy approved (1990 Europe, 1992 USA) for the treatment of metastatic melanoma in 20 years. Studies have demonstrated that IL-2 offers the possibility of a complete and long-lasting remission in this disease, although only in a small percentage of patients. Intralesional IL-2 for in-transit metastases has a high complete response rate ranging from 40 to 100%.

By 2005 a number of new agents and novel approaches were under evaluation and showed promise.

In 2009 Clinical trial participation was considered the standard of care for metastatic melanoma.

Therapies for metastatic melanoma include biologic immunotherapy agents ipilimumab, pembrolizumab, and nivolumab; BRAF inhibitors, such as vemurafenib and dabrafenib; and a MEK inhibitor trametinib.

Ongoing research is looking at treatment by adoptive cell transfer. For this purpose, application of prestimulated or modified T cells or dendritic cells is possible.

At the American Society of Clinical Oncology Conference in June 2010, the Bristol-Myers Squibb pharmaceutical company reported the clinical findings of their drug ipilimumab. The study found an increase in median survival from 6.4 to 10 months in patients with advanced melanomas treated with the monoclonal ipilimumab, versus an experimental vaccine. It also found a one-year survival rate of 25% in the control group using the vaccine, 44% in the vaccine and ipilimumab group, and 46% in the group treated with ipilimumab alone. However, some have raised concerns about this study for its use of the unconventional control arm, rather than comparing the drug against a placebo or standard treatment. The criticism was that although Ipilimumab performed better than the vaccine, the vaccine has not been tested before and may be causing toxicity, making the drug appear better by comparison.

Ipilimumab was approved by the FDA in March 2011 to treat patients with late-stage melanoma that has spread or cannot be removed by surgery.

In June 2011, a clinical trial of ipilimumab plus dacarbazine combined this immune system booster with the standard chemotherapy drug that targets cell division. It showed an increase in median survival for these late stage patients to 11 months instead of the 9 months normally seen. Researchers were also hopeful that perhaps 10–20% of patients could live a long time. Some serious side-effects of revving up the immune system were seen in some patients. A course of treatment costs $120,000. The drug's brandname is Yervoy.

Therapies for metastatic melanoma include the biologic immunotherapy agents ipilimumab, pembrolizumab, and nivolumab; BRAF inhibitors, such as vemurafenib and dabrafenib; and a MEK inhibitor trametinib.

Cimetidine works by slowing tumor growth; it is a histamine blocker that maintains the body’s immune response which aids in the killing of tumor cells. Cimetidine has not been proven to efficiently resolve tumors completely.

Cisplatin is a chemotherapy drug that is injected into the tumor itself; this drug is commonly used along with surgical removal. That being said, this drug has been shown to resolve tumors with or without surgical removal for at least 2 years.

Surgical resection of the tumor with wide margins remains the preferred method of treatment, and has shown the most success against the disease. Recently, limb-sparing surgery has been explored with moderate success.

In cases of advanced, recurrent, or metastasized disease, or if the tumor is inoperable, chemotherapy and radiation are the standard of care, although the overall success rates with these remains low.

The best treatment of lentigo maligna is not clear as it has not been well studied.

Standard excision is still being done by most surgeons. Unfortunately, the recurrence rate is high (up to 50%). This is due to the ill defined visible surgical margin, and the facial location of the lesions (often forcing the surgeon to use a narrow surgical margin). The use of dermatoscopy can significantly improve the surgeon's ability to identify the surgical margin. The narrow surgical margin used (smaller than the standard of care of 5 mm), combined with the limitation of the standard bread loafing technique of fixed tissue histology - result in a high "false negative" error rate, and frequent recurrences. Margin controlled (peripheral margins) is necessary to eliminate the false negative errors. If breadloafing is utilized, distances from sections should approach 0.1 mm to assure that the method approaches complete margin control.

Where the lesion is on the face and either large or 5mm margins are possible, a skin flap or skin graft may be indicated/required. Grafts have their own risks of failure and poor cosmetic outcomes. Flaps can require extensive incision resulting in long scars and may be better done by plastic surgeons (and possibly better again by those with extensive LM or "suspicious of early malignant melanoma" experience.

Mohs surgery has been done with cure rate reported to be 77%. The "double scalpel" peripheral margin controlled excision method approximates the Mohs method in margin control, but requires a pathologist intimately familiar with the complexity of managing the vertical margin on the thin peripheral sections and staining methods.

Some melanocytic nevi, and melanoma-in-situ (lentigo maligna) have resolved with an experimental treatment, imiquimod (Aldara) topical cream, an immune enhancing agent. In view of the very poor cure rate with standard excision, some surgeons combine the two methods: surgical excision of the lesion, then three months treatment of the area with imiquimod cream.

Studies seem to conflict about the level of certainty associated with using imiquimod.

Another treatment to be considered where standard margins cannot be achieved or cosmetics are a major consideration is ultra-soft x-ray/grenz-ray radiation.

In the very elderly or those with otherwise limited life expectancy, the impact of major day surgery for excision with 5mm margins and large skin flap could be worse than doing nothing or the possibility of failed treatments with imiquimod or Grenz ray.

Total resection of the tumour, followed by radiation therapy is the standard treatment modality. Medulloepithelioma of the ciliary body may necessitate enucleation of the eye. Radiation therapy alone may prolong survival. Aggressive chemotherapy with autologous bone marrow transplant is used for metastatic medulloepitheliomas.

Appropriate sun-protective clothing, use of broad-spectrum (UVA/UVB) sunscreen with at least SPF 50, and avoidance of intense sun exposure may prevent skin cancer.

Most squamous cell carcinomas are removed with surgery. A few selected cases are treated with topical medication. Surgical excision with a free margin of healthy tissue is a frequent treatment modality. Radiotherapy, given as external beam radiotherapy or as brachytherapy (internal radiotherapy), can also be used to treat squamous cell carcinomas.

Mohs surgery is frequently utilized; considered the treatment of choice for squamous cell carcinoma of the skin, physicians have also utilized the method for the treatment of squamous cell carcinoma of the mouth, throat, and neck. An equivalent method of the CCPDMA standards can be utilized by a pathologist in the absence of a Mohs-trained physician. Radiation therapy is often used afterward in high risk cancer or patient types.

Electrodessication and curettage or EDC can be done on selected squamous cell carcinoma of the skin. In areas where SCC's are known to be non-aggressive, and where the patient is not immunosuppressed, EDC can be performed with good to adequate cure rate.

High-risk squamous cell carcinoma, as defined by those occurring around the eye, ear, or nose, is of large size, is poorly differentiated, and grows rapidly, requires more aggressive, multidisciplinary management.

Nodal spread:

1. Surgical block dissection if palpable nodes or in cases of Marjolin's ulcers but the benefit of prophylactic block lymph node dissection with Marjolin's ulcers is not proven.

2. Radiotherapy

3. Adjuvant therapy may be considered in those with high-risk SCC even in the absence of evidence for local mestastasis. Imiquimod (Aldara) has been used with success for squamous cell carcinoma "in situ" of the skin and the penis, but the morbidity and discomfort of the treatment is severe. An advantage is the cosmetic result: after treatment, the skin resembles normal skin without the usual scarring and morbidity associated with standard excision. Imiquimod is not FDA-approved for any squamous cell carcinoma.

In general, squamous cell carcinomas have a high risk of local recurrence, and up to 50% do recur. Frequent skin exams with a dermatologist is recommended after treatment.

The treatment protocol for uveal melanoma has been directed by many clinical studies, the most important being The Collaborative Ocular Melanoma Study (COMS). The treatment varies depending upon many factors, chief among them, the size of the tumor and results from testing of biopsied material from the tumor. Primary treatment can involve removal of the affected eye (enucleation); however, this is now reserved for cases of extreme tumor burden or other secondary problems. Advances in radiation therapies have significantly decreased the number of patients treated by enucleation in developed countries. The most common radiation treatment is plaque brachytherapy, in which a small disc-shaped shield (plaque) encasing radioactive seeds (most often Iodine-125, though Ruthenium-106 and Palladium-103 are also used) is attached to the outside surface of the eye, overlying the tumor. The plaque is left in place for a few days and then removed. The risk of metastasis after plaque radiotherapy is the same as that of enucleation, suggesting that micrometastatic spread occurs prior to treatment of the primary tumor. Other modalities of treatment include transpupillary thermotherapy, external beam proton therapy, resection of the tumor, Gamma Knife stereotactic radiosurgery or a combination of different modalities. Different surgical resection techniques can include trans-scleral partial choroidectomy, and transretinal endoresection.

Treatment of small melanomas is often not necessary, but large tumors can cause discomfort and are usually surgically removed. Cisplatin and cryotherapy can be used to treat small tumors less than 3 centimeters, but tumors may reoccur. Cimetidine, a histamine stimulator, can cause tumors to regress in some horses, but may take up to 3 months to produce results and multiple treatments may be needed throughout the horse's life. There are few viable treatment options for horses with metastatic melanoma. However, gene therapy injections utilizing interleukin-12 and 18-encoding DNA plasmids have shown promise in slowing the progression of tumors in patients with metastatic melanoma.

Treatment is dependent on type of cancer, location of the cancer, age of the person, and whether the cancer is primary or a recurrence. Treatment is also determined by the specific type of cancer. For a small basal-cell cancer in a young person, the treatment with the best cure rate (Mohs surgery or CCPDMA) might be indicated. In the case of an elderly frail man with multiple complicating medical problems, a difficult to excise basal-cell cancer of the nose might warrant radiation therapy (slightly lower cure rate) or no treatment at all. Topical chemotherapy might be indicated for large superficial basal-cell carcinoma for good cosmetic outcome, whereas it might be inadequate for invasive nodular basal-cell carcinoma or invasive squamous-cell carcinoma.. In general, melanoma is poorly responsive to radiation or chemotherapy.

For low-risk disease, radiation therapy (external beam radiotherapy or brachytherapy), topical chemotherapy (imiquimod or 5-fluorouracil) and cryotherapy (freezing the cancer off) can provide adequate control of the disease; all of them, however, may have lower overall cure rates than certain type of surgery. Other modalities of treatment such as photodynamic therapy, topical chemotherapy, electrodesiccation and curettage can be found in the discussions of basal-cell carcinoma and squamous-cell carcinoma.

Mohs' micrographic surgery (Mohs surgery) is a technique used to remove the cancer with the least amount of surrounding tissue and the edges are checked immediately to see if tumor is found. This provides the opportunity to remove the least amount of tissue and provide the best cosmetically favorable results. This is especially important for areas where excess skin is limited, such as the face. Cure rates are equivalent to wide excision. Special training is required to perform this technique. An alternative method is CCPDMA and can be performed by a pathologist not familiar with Mohs surgery.

In the case of disease that has spread (metastasized), further surgical procedures or chemotherapy may be required.

Treatments for metastatic melanoma include biologic immunotherapy agents ipilimumab, pembrolizumab, and nivolumab; BRAF inhibitors, such as vemurafenib and dabrafenib; and a MEK inhibitor trametinib.

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.

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.

Excision of the entire lesion, with adequate margin, will remove the lesion, allow full tissue diagnosis, and leave a planned surgical wound which can usually be repaired with a good cosmetic result. However, removing the entire lesion (especially on the face) may present difficult problems of plastic reconstruction. (On the nose and face, Mohs surgery may allow for good margin control with minimal tissue removal, but many insurance companies require the definitive diagnosis of a malignancy "before" they are prepared to pay the extra costs of Mohs surgery.) Especially in more cosmetically-sensitive areas, and where the clinical diagnosis is reasonably certain, alternatives to surgery may include no treatment (awaiting spontaneous resolution).

On the trunk, arms, and legs, electrodesiccation and curettage often suffice to control keratoacanthomas until they regress. Other modalities of treatment include cryosurgery and radiotherapy; intralesional injection of methotrexate or of 5-fluorouracil have also been used.

Recurrence after electrodesiccation and curettage can occur; it can usually be identified and treated promptly with either further curettage or surgical excision.

2004 research showed that CCSK patients exhibit an improved relapse-free survival from a longer course of therapy when using vincristine, doxorubicin, and dactinomycin, but their long-term survival is unchanged compared with patients receiving 6 months of therapy.

Currently, there is no consensus regarding type or frequency of scans following diagnosis and treatment of the primary eye tumor. Of the 50% of patients who develop metastatic disease, more than 90% of patients will develop liver metastases. As such, the majority of surveillance techniques are focused on the liver. These include abdominal magnetic resonance imaging (MRI), abdominal ultrasound and liver function tests. The scientific community is currently working to develop guidelines, but until then, each patient must take into consideration their individual clinical situation and discuss appropriate surveillance with their doctors.

Some ophthalmologists have also found promise with the use of intravitreal avastin injections in patients suffering from radiation-induced retinopathy, a side effect of plaque brachytherapy treatment, as well as imaging surveillance with SD-OCT.

Chemotherapy is the only treatment for mesothelioma that has been proven to improve survival in randomised and controlled trials. The landmark study published in 2003 by Vogelzang and colleagues compared cisplatin chemotherapy alone with a combination of cisplatin and pemetrexed (brand name Alimta) chemotherapy in patients who had not received chemotherapy for malignant pleural mesothelioma previously and were not candidates for more aggressive "curative" surgery. This trial was the first to report a survival advantage from chemotherapy in malignant pleural mesothelioma, showing a statistically significant improvement in median survival from 10 months in the patients treated with cisplatin alone to 13.3 months in the group of patients treated with cisplatin in the combination with pemetrexed and who also received supplementation with folate and vitamin B. Vitamin supplementation was given to most patients in the trial and pemetrexed related side effects were significantly less in patients receiving pemetrexed when they also received daily oral folate 500mcg and intramuscular vitamin B 1000mcg every 9 weeks compared with patients receiving pemetrexed without vitamin supplementation. The objective response rate increased from 20% in the cisplatin group to 46% in the combination pemetrexed group. Some side effects such as nausea and vomiting, stomatitis, and diarrhoea were more common in the combination pemetrexed group but only affected a minority of patients and overall the combination of pemetrexed and cisplatin was well tolerated when patients received vitamin supplementation; both quality of life and lung function tests improved in the combination pemetrexed group. In February 2004, the United States Food and Drug Administration approved pemetrexed for treatment of malignant pleural mesothelioma. However, there are still unanswered questions about the optimal use of chemotherapy, including when to start treatment, and the optimal number of cycles to give. Cisplatin and pemetrexed together give patients a median survival of 12.1 months.

Cisplatin in combination with raltitrexed has shown an improvement in survival similar to that reported for pemetrexed in combination with cisplatin, but raltitrexed is no longer commercially available for this indication. For patients unable to tolerate pemetrexed, cisplatin in combination with gemcitabine or vinorelbine is an alternative, or vinorelbine on its own, although a survival benefit has not been shown for these drugs. For patients in whom cisplatin cannot be used, carboplatin can be substituted but non-randomised data have shown lower response rates and high rates of haematological toxicity for carboplatin-based combinations, albeit with similar survival figures to patients receiving cisplatin.

In January 2009, the United States FDA approved using conventional therapies such as surgery in combination with radiation and or chemotherapy on stage I or II Mesothelioma after research conducted by a nationwide study by Duke University concluded an almost 50 point increase in remission rates.

In pericardial mesothelioma, chemotherapy - typically adriamycin and/or cisplatin - is primarily used to shrink the tumor and is not curative.

Simple surgical excision is considered curative. Rare recurrences have been reported.

Medulloepithelioma carries a dismal prognosis with a median survival of 5 months.