The kind of cancer that apparently killed 47-year-old musician Adam Yauch is very rare, and its likely causes remain mysterious.

Yauch, who helped make the Beastie Boys band a household name in the mid 1980s, revealed three years ago that he had been diagnosed with salivary parotid gland cancer. Richard Smith, director of the Head and Neck Cancer Program at Montefiore Einstein Center for Cancer Care in Bronx, N.Y., says salivary gland cancers come in “a great variety,” affecting different specific glands within the salivary gland system and carrying differing degrees of lethality.

“Some are very benign and don’t act like cancer at all,” Smith explains, “while some are very aggressive and fatal.”

Head and neck cancers are among the least common cancers, Smith says, and those affecting salivary glands are even less common. The American Cancer Society Web site says salivary gland cancers account for fewer than 1 percent of cancers in the U.S., with 2 diagnoses per 100,000 people per year.

Smith says these cancers are more typically found in people in their 60s, though he has treated patients in their teens and early twenties who have aggressive forms of the disease. He notes that men often discover parotid gland cancers when they are shaving and feel a “mass or lump” located behind their jaw and just in front of and below their ear.  The parotid gland is the one that swells when you have the mumps, Smith says.

Salivary gland cancers often remain asymptomatic, Smith says, “unless they get big enough to press on a nerve and cause numbness or weakness.”

Treatment generally begins with surgical removal of the tumor and any lymph nodes to which the cancer may have traveled. People with aggressive forms may also receive radiation treatment, but chemotherapy is not used to combat this cancer, Smith says.

The risk factors for these cancers are not clear, Smith says. It does not appear, for instance, that smoking or alcohol consumption, which have been linked to other forms of cancer, increase the risk for salivary gland cancer. Getting this diagnosis, Smith says, is “just bad luck.”