Acinic Cell Carcinoma
Acinic cell carcinoma is an uncommon, low grade malignant tumor of the salivary glands. It dates back to 1892, when it was first described by Nasse, arising in the parotid salivary gland. Overall, salivary gland cancer comprises between 0.3%-0.9% of all cancer in the United States. Acinic cell cancer accounts for approximately 5% of all such malignant salivary tumors, and, is the third most common salivary gland tumor.
Ninety percent of the tumors arise in the parotid gland and 3% have been reported to occur bilaterally. The remainder arise in the submandibular and minor salivary glands. Very rarely, it may occur in the pancreas and the lung. The lung lesions are most commonly, metastasis from a head and neck source.
Table 1
Salivary gland cancer 0.3%-0.9% of all cancers in the United States
Acinic cell carcinoma 5% of malignant salivary gland tumors
Third most common salivary gland tumor
99% ACC arise in parotid gland – 3% occur bilaterally
Rarely occurs in pancreas and lung
What are salivary glands?
There are several different paired salivary glands found in the head and neck region. The major salivary glands are: (1) the parotid glands, which are located in front of the ears, (2) the submandibular glands, located under the jawline, and (3) the sublingual glands, located on the floor of the mouth along the submandibular gland ducts. The minor salivary glands are microscopic collections of salivary tissue; they are diffuse in the mouth and are primarily located in the lips, tongue, palate (or roof of mouth), cheek, nose, sinuses and larynx (or voice box). All saliva glands produce saliva (or spit), which is a lubrication fluid that moistens the mouth and begins food digestion. In addition, saliva also contains antibodies that help protect against tooth decay and prevent infection in the mouth and throat.
Salivary glands are made up of several different cells types. Tumors or cancers can grow from any of these cells in the gland. Usually, the tumors are named according to which of these cells they most look like under the microscope. The acinic tumor cells are similar to the acinar serous cells in the secretory unit in the gland, thus, the name acinic cell carcinoma. These serous cells are found predominately in the parotid gland. This accounts for the high occurrence in this gland compared to the other salivary glands.
Insert diagram of secretory unit.
Clinical Presentation
Acinic cell carcinoma affects women more commonly than men. It may occur at any age, although, the peak occurrence is seen in the mid 40’s to 50’s age group. ACC may present with any of the following symptoms:
* A swelling or mass in the face, neck or mouth that slowly enlarges over a long period of time.
* A difference between the size or shape of the left and right sides of your face
* If the tumor invades the facial nerve, there may be numbness in a part of the face or weakness on one side of the face. It may or may not involve pain. Less than one third of patients report pain with the swelling or masses.
* These tumors may easily go undiagnosed due to the slow growth, low grade and absence of pain. It has been reported to metastasize (spread to another body part) to the lymph nodes in approximately 16% of patients. The most common areas of metastases are the lungs and bone.
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Evaluation and Diagnosis
If you experience any of the symptoms noted above you should be referred to an Otolaryngologist who specializes in head and neck cancer. An otolaryngologist will take a detailed history and perform a head and neck exam. Once you are examined, the doctor may order a MRI, CT or PET CT scan to determine extent of disease in the gland and spread to other areas in the body. A sample of tissue may be taken from the mass by fine needle aspiration. A fine needle aspiration will obtain cells from the tumor to be examined by a pathologist. The pathologist will determine the cell type and make a tissue diagnosis.
Staging and Treatment
After the physical exam, x-rays and biopsy are completed the tumor will be staged. Staging is the process of finding out if and how far the cancer has spread and is based on tumor size, spread to lymph nodes and spread to distant organs (metastasis). There are four separate groups (I, II, III, and IV) Stages I and II are smaller tumors that have not spread and generally have a better prognosis.
Stages III and IV represent more advanced tumors that have metastasized. This is very important because the treatment will depend on the stage of the tumor. ACC treatment may include surgery, radiation therapy, chemotherapy or a combination of 2 of these methods.
The Parotid Gland and Parotidectomy
ACC most frequently arises in the parotid gland. These glands are the largest of the paired salivary glands and are located on each side of face in front of the ear/jaw. The facial nerve arises in the brain and exits the skull just in front of the ear canal and enters into the gland. The nerve splits into branches and travels throughout the whole gland dividing the gland into the superficial and deep lobes. The superficial lobe lies on the surface of the facial nerve. This nerve controls the muscles of facial expression; forehead wrinkling, eyebrow raising, eyelid squinting/blinking, lip puckering and smiling.
The treatment of choice for Stage I and II is complete surgical excision with a negative margin (a half inch rim of normal tissue around the tumor). A parotidectomy is the removal of the parotid gland. Depending on the size and location of the tumor a superficial or deep parotidectomy will be preformed. An incision is made in front of the ear, travels down and around the earlobe, then extends under the mandible. In this procedure the head and neck surgeon must identify the intricate branches of the facial nerve. A nerve monitor is used to check for nerve function. A superficial parotidectomy with nerve sparing is preformed when the tumor is superficial. If the tumor is deeper, the nerves branches are teased away from the tumor and left intact. Rarely, the nerve is invaded and must be sacrificed. A neck dissection is necessary for those patients with Stage III and IV cancer. This involves removing the lymph nodes (bean sized tissue of immune cells that help fight infections and cancer) in the anterior aspect of the neck.
Radiation therapy is the treatment indicated in high grade advanced tumors (Stages III and IV) and when there are positive surgical margins. Radiation therapy uses high energy rays to kill or shrink cancer cells to prevent further metastasis. Chemotherapy, which uses drugs to kill cancer cells, is not used very often to treat ACC but can be used when there are distant metastasis, to help control pain, or in combination with radiation.