Unlike basal cell carcinoma, the three rare skin cancers highlighted here are quite uncommon. They are important to know about, however, because they may be mistaken for more other benign conditions, such as a bug bite or, if on the eyelid, a stye. This can lead to a delay in diagnosis that could impact the prognosis.
Sebaceous carcinoma is a very rare type of tumor. It has an estimated incidence rate of 0.32 (male) and 0.16 (female) per 100,000 person-years in the United States. It is an aggressive malignant tumor that arises from a sebaceous (oil) gland in the skin.
This tumor is known as “the great masquerader” as it is often mistaken for a benign growth such as a chalazion or stye or a different kind of malignant tumor. This masquerading often leads to a delay in diagnosis.
Two groups of sebaceous carcinomas
Sebaceous carcinomas can be separated into two groups: ocular and extraocular.
1. Ocular tumors
Ocular tumors develop around the eyes, most commonly from meibomian glands on the eyelid. Tumors occur 2 to 3 times more frequently on the upper eyelid compared to the lower eyelid.
They often begin as a skin lump or thickening of the skin around the eye. As they grow, sebaceous carcinomas may bleed.
Ocular sebaceous carcinoma is an aggressive tumor. It may reoccur locally as well as spread to other parts of the body. Early diagnosis is essential as these rare tumors have a significant mortality rate of about 22%.
2. Extraocular tumors
Extraocular sebaceous carcinomas account for 20% of these tumors. They most commonly occur on the head and neck regions including the scalp and face. Rarely these tumors can be diagnosed on the trunk, extremities or genital areas where they may appear as a yellow bump on the skin.
The exact cause of sebaceous carcinoma is unknown
The exact cause of sebaceous carcinoma is unknown. They occur more commonly in the elderly. However, they can also occur in younger patients, especially those who have had radiation to the face.
Women are affected more than men. And there is a higher incidence among Asians.
The primary treatment is surgical
Surgical removal is the primary method of treatment to prevent local or systemic spread. Lymph node evaluation is often necessary to determine whether there has been metastatic spread of the tumor. In rare cases where orbital disease is unresectable, complete removal of the eye orbit contents, exenteration, is necessary.
Cryotherapy, topical chemotherapy and radiation therapy are also used as adjunctive therapy and for patients who decline surgical excision or exenteration. Multiple therapy modalities have been shown to improve survival rates and physical outcome.
A poor prognosis is associated with involvement of both the upper and lower lid, poor differentiation on histopathology, symptoms lasting longer than 6 months, tumor size exceeding 10 mm, and vascular, lymphatic and orbital invasion.
Merkel Cell Carcinoma
Merkel Cell Carcinoma (MCC) is also known as neuroendocrine carcinoma of the skin. It is a very rare aggressive type of skin cancer that is the result of uncontrollable growth of a Merkel cell.
Normal Merkel cells are located at the base of the epidermis. They are most commonly associated with underlying sensory nerve endings and function predominately as touch receptors in the skin.
Merkel cell carcinomas often appear as a pink-red or bluish-red firm, dome-shaped nodules. These painless lumps may be mistaken for a bug bite or another more common type of skin lesion, the basal cell carcinoma.
The American Cancer Society reports that approximately 2,000 new cases of Merkel Cell Carcinoma are diagnosed annually in the United States.
Merkel cell carcinoma can grow very quickly and commonly spreads to other parts of the body
Cause of Merkel Cell Carcinoma
Although the exact cause of Merkel cell carcinoma is unknown, researchers have recently discovered a virus, the Merkel cell polyomavirus (MCV), that resides harmlessly on the skin in most people. It is found in the cancer cells of about 8 out of 10 people with MCC. But because MCV is so common and MCC is so rare, it is not clear what role this virus plays in the development of MCC.
-Exposure to ultraviolet light from either sunshine or tanning beds is a known risk factor for most skin cancers and MCC is no exception. MCCs are much more likely to develop on sun-exposed skin, such as the face, neck, and arms.
-Light skin color: the incidence of MCC is much higher in those with light skin compared to darker complected individuals.
-Age: although MCC can occur at any age, the majority of individuals diagnosed with MCC are over 70 years of age.
Weakened immune system: Individuals with weakened immunity are at increased risk of developing MCC. Patients with leukemia, lymphoma, HIV infection or those being treated with immunosuppressive chemotherapy or other drugs to prevent transplant rejection may be at increased risk.
Once a Merkel cell carcinoma is diagnosed, and studies are performed to determine if the tumor has spread treatment options might include:
-Surgery is the most common treatment for Merkel Cell Carcinoma. The tumor is removed in addition to a margin of normal skin surrounding the tumor to assure the complete removal of the cancer. Often times, regional lymph nodes in the area of the tumor are removed at the same time to assess whether the tumor has spread. Spread to lymph nodes is found in approximately one-half of patients.
-Radiation Therapy. Following surgery, localized radiation therapy at the tumor site is commonly used to destroy remaining cancer cells. Radiation therapy is also used in patients when surgery is not an option due to ill health, certain tumor locations or if the tumor has reoccurred after initial treatment.
-Chemotherapy. Following surgery, chemotherapy may be initiated especially when Merkel cell carcinoma has spread to lymph nodes, distant parts of the body, or has reoccurred after initial therapy.
When diagnosed and treated early, Merkel cell carcinoma can be treated and even cured.
Unlike the most common skin cancers that arise from cells in the epidermis, dermatofibrosarcoma protuberans (DFSP) is a rare skin cancer that develops from the dermis, the middle layer of the skin.
DFSP tends to grow very slowly. It rarely spreads to other parts of the body and so has a high rate of survival. DFSP tumors, however, can grow deep into the surrounding fat and soft tissues including the muscle and bone.
Dermatofibrosarcoma protuberans can develop anywhere on the body but is most common on the arms, legs, or torso.
Initially, DFSP appears as a bruise or scar. However, as it grows, a lump of skin commonly develops on the skin surface (protuberans). Although these tumors are initially painless and without symptoms, as they grow they may become tender, crack or bleed.
Once the lumps appear, DFSP tends to grow more quickly. DFSP may appear reddish brown, pink, or violet. In children, DFSP may be mistaken for a simple birthmark.
DFSP occurs in people of all ages but it is most frequently diagnosed in individuals between 20 and 50 years of age. The tumor can sometimes begin on skin that has been injured by a previous burn or surgery. However, the exact cause of DFSP is unknown.
Treatment of DFSP
-Excision (surgery). The majority of patients with DFSP are treated with surgery. The DFSP tumor and a margin of healthy skin are excised to assure complete removal of the cancerous growth.
-Mohs Micrographic Surgery. Large tumors that may grow in irregular shape are often treated with Mohs Micrographic Surgery, a specialized type of surgery that involves removing and assessing layers of the tumor until only cancer-free tissue remains.
-Radiation therapy. Radiation therapy is used to destroy cancer cells when surgery is not an option or with DFSP reoccurrences after surgery.
-Targeted Drug therapy. The FDA has approved targeted drug therapy with drugs that attack certain cancer cells. Imatinib (Gleevac) can target certain DFSP cells that make an excess of a particular protein. This drug therapy may be warranted in the following circumstances:
- when DFSP reoccurs after surgery
- if the tumor has spread to other areas of the body
- when surgery is not an option
-Reconstructive surgery. Because DFSP can grow deep into the skin, some patients may require reconstructive surgery to repair the wound caused by the surgical removal of the cancerous tumor.
Because DFSP rarely spreads to other parts of the body, patients most often live for many years after treatment. Close lifelong follow up with dermatologists and medical professionals is warranted for all patients who have been treated for DFSP.
The bottom line on rare skin cancers
Although rare, sebaceous carcinoma, Merkel cell carcinoma, and dermatofibroma sarcoma protuberans (DFSP) are important to know about. This is because they may be mistaken for other more benign conditions, delaying their diagnosis and impacting their prognosis.
If you develop any suspicious lumps or bumps on your skin, including your eyelid, be sure to see a dermatologist for a definitive diagnosis.
Other articles on skin cancer by Fayne Frey, M.D.:
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Originally published 1/27/19, it has been reviewed by the author. Two new references were added to the sections on surgical treatments of sebaceous carcinoma and DFSP).