Parotid Cancer

Clinicians are always worried about missing what we call "the zebra" among the horses. Parotid cancer would be one of those zebras. It's rare and it's symptoms can be misleading. The parotid gland is the largest of the major salivary glands located on either side of the face, or rather both sides of the face, just in front of the ears and over the jaw. They produce a thin, watery saliva that aids in digestion by offering us the enzyme, amylase, digesting starches. The parotid glands produce about a quarter of our total saliva as well, particularly during meals. Important to appreciate is that the facial nerve passes right through the gland on either side.

When we have the mumps, as I did in third grade, our parotid gland becomes painfully swollen due to a viral infection. Our parotid glands aren't normally palpable, but when infected they are quite swollen so that we look as if we have "chipmunk cheeks." The mumps virus is contagious through our saliva, either by sneezing, coughing, or sharing utensils. Parotid swelling is a classic sign of the virus, with swelling lasting for several days.

Salivary Gland Malignancies are Relatively Rare

Parotid gland cancer is rare, usually slow-growing malignancy in the salivary gland near the ear, with 80% of tumors being benign. More cases are noticed in areas of higher ultraviolet radiation (Ho et al., 2011). Certainly cancer can happen in anyone, at any age, but parotid cancer is more common in men, and more often found after the age of 55 years, most commonly at 64 years of age.

Salivary gland tumors account for about 5% of all neoplasms of the head and neck, three-quarters occurring in the parotid glands (Ho et al., 2011). Only about 20% are malignant. The five-year relative survival rate for salivary gland cancer depends on the stage of the cancer.

Symptoms include a persistent, often painless lump on the face or neck, even the ear, or this area may be numb. Sometimes there is facial weakness because of its relationship to the facial nerve. These lumps are typically removed, called a parotidectomy, combined with radiation. Malignant tumors can be quite painful and cause difficulty with swallowing or even difficulty in opening the mouth.

Long-term pleomorphic adenomas, a benign tumor, can turn malignant. This risk increases over time, so about 1.5% are malignant at 5 years, but by 15 years, 9.5% are malignant. Sometimes squamous cell carcinoma spreads, or even melanoma from the head or face, to the lymph nodes and then ends up in the parotid gland. These glands can also be damaged from radiation treatment to the head or neck.

Dentists are often the specialists identifying these tumors, although they can be found in the convenience or urgent care as well, because individual's may perceive that they have an ear infection. The primary care provider will order an MRI or CT scan to further evaluate, sometimes a PET scan. This helps us understand the tumor size and its spread, if any. This will then be followed with a biopsy, via fine-needle aspiration, to determine if the tumor is benign or malignant. If the cancer has spread beyond the neck, then chemotherapy would be recommended.

The outlook of parotid cancer depends heavily on the stage and histological type of the cancer. Low-grade tumors found in early stage, and removed completely, have a high likelihood of good outcome. When they are high-grade though, they are more aggressive so do have a higher risk of recurrence. From stage I to IV, the rates of survival for salivary gland cancer are 96%, 77%, 73%, and 37%, respectively (Ho et al., 2011).

One of the reported side effects of radiation as treatment for parotid gland cancer is hearing loss (Ho et al., 2011). Studies are underway to determine what intensity provides relief of malignancy, but spares the cochlear sensory-neural hearing loss.

Etiology Has Not Been Thoroughly Studied

Factors related to why are still a bit unclear, but as one could imagine, exposures to tobacco smoke and alcohol intake have not been found consistently associated with its development (Ho et al., 2011). The well-established risk is exposure to ionizing radiation based on studies focusing on survivors of the atomic bomb. Linear dose-dependent relationships have also been observed. Medical radiation or ultraviolet light therapeutic treatments to the head and neck and exposures to full-mouth dental X-rays have also been linked to increased risk. This seems to be a bit more risky for those who are fair-skinned, already more sensitive to the effects of UV light. Additionally, nitroso compounds have also induced parotid gland tumors in laboratory mice, which are found in rubbers so these industrial workers are at risk.

References

Ho, K., Lin, H., Ann, D. K., Chu, P. G. & Yen, Y. (2011). An overview of the rare parotid gland cancer. Head Neck Oncol, 3(40).