Desmoplastic melanoma

Melanoma is a rare but dangerous form of skin cancer that develops in melanocytes, the pigment-producing cells that give skin its color. Desmoplastic melanoma (DM) is an extremely rare form of the disease.

What is desmoplastic melanoma?

Desmoplastic melanoma is a type of spindle cell melanoma that's more common in male patients than females.

A disease that’s often difficult to identify, desmoplastic melanoma usually lacks pigmentation, commonly resembling benign growths or less dangerous skin cancers (such as basal or squamous cell carcinomas).

According to the American Cancer Society, about 1 percent of all skin cancers are melanomas, and of these melanomas, reviewers in the Journal of the American Academy of Dermatology note that less than 4 percent are desmoplastic melanomas, or tumors characterized by cancerous cells and fibrous tissue with large amounts of collagen.

Types of desmoplastic melanoma

Desmoplastic melanomas may arise on their own or from existing melanomas (most often the lentigo maligna type), and fall into one of the subtypes listed below, as categorized in the Journal of the American Academy of Dermatology:

• Pure DM (pDM): More than 90 percent desmoplastic
• Mixed DM (mDM): Less than 90 percent desmoplastic

The pure subtype is less aggressive than the mixed subtype and not as likely to spread to the lymph nodes.

What causes desmoplastic melanoma?

The main cause of this type of melanoma, as with other skin cancer types, is exposure to natural or artificial ultraviolet (UV) rays.

Desmoplastic melanomas most often develop on the head and neck or other areas that have received heavy sun exposure over a person’s lifetime. Because DM is so uncommon, it hasn’t been heavily studied. However, genetic mutations caused by exposure to UV rays are the main cause of desmoplastic melanoma.

Desmoplastic melanoma risk factors

In addition to UV light exposure, the following factors also are associated with an increased risk for developing desmoplastic melanoma:

• Gender, with men more likely than women to develop DM
• Age, particularly older patients in their 60s to 80s
• Chronic UV exposure
• Skin that’s fair or burns easily
• Previous melanoma

Desmoplastic melanoma symptoms

Desmoplastic melanoma (DM) may initially look like a scar, with patches of skin that appear thickened and are either pink or the same tone as the rest of the patient's skin.

Though DM is most often located on the head or neck, it may also be found on:

• Arms
• Legs
• Chest
• Back

Desmoplastic melanomas may be difficult to differentiate from noncancerous growths because they’re often amelanotic, meaning they lack pigmentation.

Possible symptoms include:

• Scar-like appearance with a varying surface texture
• Borders that may be either regular or irregular
• Lesions that may be flat, raised or resemble thickened skin
• Size of more than 6 millimeters (mm), typically with a diameter of 1-2 centimeters (cm); usually desmoplastic melanomas aren’t diagnosed until they’ve progressed to a larger size
• Pink or skin-tone color (though lesions may have darker spots and coloration)

Desmoplastic melanomas are tricky to identify because they don’t neatly follow the ABCDEs, or typical characteristics of melanomas:

• Asymmetrical
• Uneven borders
• Color that is black, brown or tan
• Dark with a diameter greater than 1/4 inch
• Evolving

Because early detection is difficult, and because the disease is so rare, desmoplastic melanoma is most often diagnosed in its more advanced stages.

How is desmoplastic melanoma diagnosed?

To diagnose desmoplastic melanoma, the doctor gathers the patient’s full medical history, both personal and familial. Touching the area is an important part of diagnosis, too, because a distinct feature of most DM lesions is hardening of the area.

A dermoscopy may be done, in which the skin is examined with a device called a dermoscope (handheld visual aid). In addition, the patient may undergo a biopsy of the entire lesion (called an excision).

A pathology report with the biopsy results typically is sent to the doctor. The pathology report may include:

• Subtype of the melanoma, pure or mixed
• Breslow thickness, a vertical measurement of the origin of the lesion to its deepest point
• Clark Level of Invasion, which measures the depth of the lesion

Additional imaging and blood tests may be performed as well.

Desmoplastic melanoma treatment

First-line treatment of desmoplastic melanoma consists of surgical excision, completely removing the lesion along with a margin of tissue around it. The amount of healthy tissue removed is individualized and based on the depth and thickness of the patient’s melanoma.

For lesions that are more advanced (usually greater than 4 mm), radiation therapy may also be recommended.

Checkpoint inhibitors (immunotherapy drugs that boost the immune system to fight against cancer cells) may also be used to treat desmoplastic melanomas, but research is ongoing, according to the National Cancer Institute. Clinical trials for the checkpoint inhibitor Keytruda^® (pembrolizumab) have offered promising results.

Desmoplastic melanoma survival rate

When compared with the survival rates of all melanomas, desmoplastic melanoma survival rates tend to be slightly higher.

The five-year relative survival rate represents the percentage of people still alive five years after a cancer diagnosis compared with people who don’t have that type of cancer. According to a 2017 study in ePlasty, the five-year survival rate for desmoplastic melanoma is 75 percent, and five-year disease-free survival is 62 percent.

While the survival rates of desmoplastic melanoma are promising overall, there’s still a lot about this type of melanoma—and others—that researchers don’t know yet.