Desmoplastic melanoma is a rare form of melanoma, a skin cancer that arises from pigment cells (melanocytes). Desmoplastic melanoma often involves nerve fibres, when it is called neurotropic melanoma.
What is desmoplastic melanoma?
Desmoplastic melanoma is a form of melanoma in which the malignant cells are surrounded by fibrous tissue.
Desmoplastic melanoma is an invasive form of melanoma, i.e. there are melanoma cells proliferating within the dermis or deeper tissues of the skin. It sometimes arises within a lentigo maligna, a type of melanoma in situ.
Who gets desmoplastic melanoma?
Desmoplastic melanoma accounts for about 1% of melanoma in Australia and New Zealand. It usually occurs in white skinned individuals.
Desmoplastic melanoma is more common in males (65%) than females. Most are elderly.
The main risk factors for desmoplastic melanoma are:
- Increasing age
- Previous invasive melanoma or melanoma in situ
- Fair skin that burns easily
- Sun damaged skin
What does desmoplastic melanoma look like?
Desmoplastic melanoma is most common on exposed areas of the head and neck (>50%).
The lesion presents as a slowly-enlarging area of thickened skin, sometimes described as scar-like. It is often skin coloured but may be pigmented. It may resemble a hypertrophic or keloid scar (but with no history of injury at the site), an unusual mole, dermatofibroma or neurofibroma. It becomes more distinctive in time, often growing over months to years before it is recognised. The characteristics of desmoplastic melanoma include:
Desmoplastic melanoma presents as a slowly growing lump within the skin.
- Larger size – >6 mm and often 1-2 centimetres in diameter at diagnosis
- Rounded or irregular
- Variable pigmentation – most often skin-coloured or pink nodule
- Firm scar-like nodule with a smooth or irregular surface
Deep invasive melanoma often has the following features:
- Thickening of part of the lesion
- Increasing number of colours, especially blue or black
- Ulceration or bleeding
- Itching or stinging
Desmoplastic melanomas usually lack the ABCD melanoma warning signs. (Asymmetry, Border irregularity, Colour variation, large Diameter).
What is the cause of desmoplastic melanoma?
Desmoplastic melanoma is due to the development of malignant pigment cells (melanocytes) within dermis. These cells may arise within another type of melanoma or in previously normal-appearing skin. What triggers the melanocytes to become malignant is unknown, but it is likely to be a series of changes to DNA.
What tests should be done?
It is essential to diagnose desmoplastic melanoma accurately. Clinical diagnosis is aided by dermoscopy and skin biopsy (usually excision biopsy). Those with melanoma that is more than 1 mm thick may be advised to have lymph node biopsy, imaging studies and blood tests.
Dermoscopy, or the use of a dermatoscope, by a dermatologist or other doctor trained in its use can be helpful in distinguishing desmoplastic melanoma from other skin lesions, such as:
The most frequently observed dermoscopic features of desmoplastic melanoma are:
- Features of melanocytic lesion in 50% (pigmented globules or network)
- Asymmetrical structure and colours
- Regression features: scar-like areas, grey dots
- Multiple colours
- Atypical or polymorphous vascular pattern
If the skin lesion is suspicious of desmoplastic melanoma, it should be urgently cut out (excision biopsy).
The pathological diagnosis of melanoma can be very difficult. Desmoplastic melanomas have little or no spread of malignant cells within the epidermis; the melanoma cells are atypical spindle cells separated by a fibrous stroma and are found within the dermis or subcutaneous fat. Nerve infiltration or neurotropism is found in about half of desmoplastic melanomas. Extra tests using immunohistochemical stains such as S100 may be necessary.
The pathologist's report should include a macroscopic description of the specimen and melanoma (the naked eye view), and a microscopic description.
- Diagnosis of primary melanoma
- Breslow thickness to the nearest 0.1 mm
- Clark level of invasion
- Margins of excision i.e. the normal tissue around the tumour
- Mitotic rate – a measure of how fast the cells are proliferating
- Whether or not there is ulceration
The report may also include comments about the cell type and its growth pattern, invasion of blood vessels or nerves, inflammatory response, regression and whether there is an associated naevus (original mole) of other form of melanoma.
Desmoplastic melanoma may be reported to be 'pure' or 'mixed', depending on the extent of 'desmoplasia' i.e. fibrosis around the melanoma cells.
What is Breslow thickness?
The Breslow thickness is reported for invasive melanomas. It is measured vertically in millimetres from the top of the granular layer (or base of superficial ulceration) to the deepest point of tumour involvement. In most melanomas, it is a strong predictor of outcome; the thicker the melanoma, the more likely it is to metastasise (spread). However, Breslow thickness has been found to be less predictive of metastasis in desmoplastic melanoma than in other types of melanoma.
What is the Clark level of invasion?
The Clark level indicates the anatomic plane of invasion. The deeper the Clark level, the greater the risk of metastasis (secondary spread). It is not considered useful in predicting outcome in desmoplastic melanoma.
What is the treatment for desmoplastic melanoma?
The initial treatment of a desmoplastic melanoma is to cut it out; the lesion should be completely excised with a 1 to 2 cm margin of normal tissue.
Melanoma staging means finding out if the melanoma has spread from its original site in the skin. Most melanoma specialists refer to the American Joint Committee on Cancer (AJCC) cutaneous melanoma staging guidelines (2009). In essence, the stages are:
|Stage 0||In situ melanoma|
|Stage 1||Thin melanoma <2 mm in thickness|
|Stage 2||Thick melanoma > 2 mm in thickness|
|Stage 3||Melanoma spread to involve local lymph nodes|
|Stage 4||Distant metastases have been detected|
Should the lymph nodes be removed?
If the local lymph nodes are enlarged due to metastatic melanoma, they should be completely removed. This requires a surgical procedure, usually under general anaesthetic. If they are not enlarged, they may be tested to see if there is any microscopic spread of melanoma. The test is known as a sentinel node biopsy.
In New Zealand, many surgeons recommend sentinel node biopsy for melanomas thicker than 1 mm, especially in younger persons. However, although the biopsy may help in staging the cancer, it does not offer any survival advantage. The necessity for sentinel node biopsy is controversial at present and its role in desmoplastic melanoma is uncertain.
Lymph nodes containing metastatic melanoma often increase in size quickly. An involved node is usually non-tender and firm to hard in consistency. If this occurs between planned follow-up visits, let your doctor know promptly.
If the melanoma is widespread, other forms of treatment may be necessary, but are not always successful in eradicating the cancer. Immunotherapy, biologics such as ipilimumab, and the BRAF inhibitors dabrafenib and vemurafenib are showing promise.
What happens at follow-up?
The main purpose of follow-up is to detect recurrences early but it also offers an opportunity to diagnose a new primary melanoma at the first possible opportunity. A second invasive melanoma occurs in 5-10% patients; an unrelated melanoma in situ affects in more than 20% of melanoma patients.
The Australian and New Zealand Guidelines for the Management of Melanoma (2008) make the following recommendations for follow-up for patients with invasive melanoma.
- Self skin examination
- Regular routine skin checks by patient's preferred health professional
- Follow-up intervals are preferably six-monthly for five years for patients with stage 1 disease, three-monthly or four-monthly for five years for patients with stage 2 or 3 disease, and yearly thereafter for all patients.
- Individual patient’s needs should be considered before appropriate follow-up is offered
- Provide education and support to help patient adjust to their illness
The follow-up appointments may be undertaken by the patient's general practitioner or specialist or they may be shared.
Follow-up appointments may include:
- A check of the scar where the primary melanoma was removed: desmoplastic melanoma can recur at the original site (local recurrence)
- A feel for the regional lymph nodes
- A general skin examination
- A full physical examination
In those with more advanced primary disease, follow-up may include:
- Blood tests, including LDH
- Imaging: ultrasound, X-ray, CT, MRI and/or PET scan.
Tests are not typically worthwhile for stage 1/2 melanoma patients unless there are signs or symptoms of disease recurrence or metastasis. And no tests are thought necessary for healthy patients who have remained well for 5 years or longer after removal of their melanoma, whatever stage.
What is the outlook?
The risk of spread and ultimate death from invasive melanoma depends on several factors, but the main one is the measured thickness of the melanoma at the time it was surgically removed. Desmoplastic melanomas may have a slightly better prognosis compared to other subtypes of the same thickness.
A study of 1129 desmoplastic melanoma patients in the United States (1992-2007) reported a 5-year specific survival rate of 85% and 10-year survival of 80%. Older age, anatomic site of the head and neck and tumour thickness >2 mm, ulceration, lymph node involvement and non-receipt of surgery were associated with lower survival. A second study of 1,735 desmoplastic melanoma patients, also in the United States (1988-2006), reported overall survival at 5 years to be 65% and that wide local excision was associated with increased survival. Traditional prognostic factors such as Breslow thickness, nodal positivity, and ulceration did not predict survival in this group of patients.