What to know about Merkel cell carcinoma, the rare skin cancer that led to the death of Jimmy Buffett

"Margaritaville" singer Jimmy Buffett died on Sept. 1 after a four-year battle with a rare skin cancer.

Buffet's website revealed he had been diagnosed with Merkel cell carcinoma, but had been able to perform until recently, when his health began to decline.

Here's what you need to know about MCC, including signs and symptoms, what causes it and how it's treated.

What is MCC?

Merkel cell carcinoma is much less common than the main types of skin cancer, such as basal cell carcinoma, squamous cell carcinoma and melanoma.

MCC is very rare -- about 40 times rarer than melanoma -- with an estimated 3,000 cases every year in the U.S., according to the Skin Cancer Foundation (SCF).

MCC is a neuroendocrine cancer, meaning it is a cancer of the cells that are connected to nerves, which likely play a role in touch sensation.

It is a rare, aggressive form of cancer that has a high risk of recurring and spreading within two to three years of being initially diagnosed, the SCF says.

What are the symptoms?

The first symptom of MCC is typically a fast-growing, painless tumor on part of the skin that is sun-exposed, according to the National Cancer Institute.

The nodules are usually shiny or pearly and may appear skin-colored in shades of red, blue or purple. However, they may appear dome-shaped or raised, firm or itchy, the Cleveland Clinic says.

A health care provider, such as a dermatologist, may perform a full-body skin exam to look for any abnormal spots as well as an exam of the lymph nodes because the cancer can spread quickly.

If the provider suspects MCC, they may perform a biopsy, which includes removing skin cells so they can be examined for signs of cancer.

What are the stages of MCC?

After a diagnosis is made, a patient's lymph nodes are often checked because of how quickly MCC can spread to this region, according to the SCF.

The next step is staging to identify how far along the cancer is. For this, the medical team will use the TNM system.

"T" stands for size of the original tumor, "N" for whether it has spread to the lymph nodes and "M" for metastasis, or spread.

Stage 0 indicates MCC cells have been found but not beyond the top layer of skin, the SCF says. Stages 1 and 2 involve smaller and larger tumors, respectively. In stage 2, the tumors may have spread to connective tissue, muscles or bones.

In stage 3, the tumors have spread to the lymph nodes or a lymph vessel between the original tumor and the nodes. In stage 4, the tumors have spread to the lymph nodes, organ or other parts of the body.

How is MCC treated?

Although MCC is rare, it is treatable when found in an early stage.

Depending on the stage of the disease and the patient's health, treatment involves surgically removing any tumors and potentially chemotherapy, radiation or immunotherapy.

If the cancer has spread to the lymph nodes, a patient may undergo a lymph node dissection, which is a surgical procedure in which some or all of the lymph nodes are removed.

How can I prevent MCC?

Males, those older than age 70, those with weakened immune systems and people with light-colored skin are more likely to develop MCC, according to the American Cancer Society.

Although these risk factors cannot be controlled, there are some steps that can be taken to lower the odds of MCC diagnosis.

This includes undergoing annual skin checks with a dermatologist, performing skin checks at home, lowering exposure to ultraviolet rays either from the sun or tanning beds and to practice sun safety when outdoors, such as covering the skin, wearing sunscreen and using hats or sunglasses.

ABC News' Dr. Mark Abdelmalek contributed to this report.