Acinic cell carcinoma overview

# Overview
Acinic cell carcinoma (ACC) is a low-grade malignant salivary neoplasm that constitutes approximately 17% of primary salivary gland malignancies. In the head and neck region, the parotid gland is the predominant site of origin. This tumor is usually a low-grade, highly differentiated carcinoma. Women are usually more frequently diagnosed than men.  There are many risk factors, including cigarette smoking, genetic predisposition, radioactive substances, viral infections, rubber manufacturing, plumbing equipment and some types of woodworking, as well as asbestos mining and exposure to nickel compounds. Patients typically present with a slowly enlarging mass in the parotid region, nausea, vomiting and digestion problems. Treatments include complete surgical resection, chemotherapy, and radiation therapy. Acinic cell carcinoma was considered as a benign neoplasm until 1953. All acinic cell carcinomas were classified as neoplasms in the WHO's international classification of disease for oncology by 1972. In a second edition, all acinic cell carcinomas considered as adenocarcinoma by 1990. Batsakis et al, described acinic cell carcinoma as a derivative from progenitor reserve cells of terminal tubules and intercalated ducts of salivary tissue for the first time. Acinic cell carcinoma, a salivary gland tumor, mainly develop in parotid gland (81000 out of 100000), less common, it occurs in the submandibular gland and minor salivary glands of palate. It belongs to the family of adenocarcinoma which share similarities with: Adenoid cystic, Muco-epidermoid, low-grade adenocarcinoma and some breast cancers. The development of acinic cell carcinomas is the result of multiple genetic mutations that suggest association of tumor suppression genes such as: Chromosome 5q, chromosome 6p, chromosome 17p, deletions of chromosome 6q, loss of chromosome Y, Trisomy 21. Molecular studies suggest that retinoblastoma pathway also can be involved with acinic cell carcinomas. Acinic cell carcinoma is a head and neck tumor happening in the salivary glands. If a patient was observed with related signs, the tumor must be classified as a benign or invasive by the capsule being intact. Differential diagnosis of a malignant tumor in salivary gland is made after the incision and by histology features which will provide a good chemotherapy regimen for so called patients. In western countries, salivary gland carcinomas account for 4000 out of 100000 of all head and neck carcinomas, and approximately 80% of those occurring in parotid gland. one out of six parotid gland cancer is acinic cell carcinomas. Distribution of acinic cell carcinoma between age groups seems to be quiet even, with a median age of 52 years, but it occurs mostly at a younger age. Children are rarely affected with salivary gland carcinoma, but if they are, it is most likely to be acinic cell carcinoma. Acinic cell carcinoma is predominantly seen in in whites (85000 out of 100000 cases) and less in African nations(8000 out of 100000 cases) here is a higher incidence among female with the ratio ranging from 1.43:1 to 1.57:1. There is very little approved information about acinic cell carcinoma risk factors but familial predisposition and previous radiation exposure may play an important role. Screening is not recommended for acinic cell carcinoma. Once diagnosis confirmed, ultrasonography, nuclear scans, CT scan and MRI can usually conduct for assessing the size of the tumor, location, and the nature of the tumor. Parotid gland, is the most common site for acinic cell carcinoma affection. Typically, acinic cell carcinoma is a slow growing mass, lacking other symptoms. Pain or fixation to surroundings is a sign of poor prognosis. Nodal metastasis of acinic cell carcinoma is extremely rare. Another rare complication is cranial nerve VII dysfunction. A small minority of of acinic cell carcinoma occurs in sinonasal area or larynx, there is a big controversy about bilateral acinic cell carcinoma, it is still unknown if it invades bilateral glands or just a unilateral tumor. Common sites for non-salivary acinic cell carcinoma is lacrimal gland, pancreas, and breast. Acinic cell carcinoma in pancreas are so called as acinar cell carcinoma. The prognostic factors are age, pain, gender, race, previous inadequate treatment, extent of disease and invasion of the skull base. Physical examination of neck may reveal a firm swelling and tenderness. Clinical stage, particularly tumor size, may be the critical factor to determine the outcome of salivary gland cancer and may be more important than histologic grade. TNM system is the system of choice for studying acinic cell carcinoma. Acinic cell carcinoma is usually anatomically accessible tumor and patient do not show far metastasis at the time of diagnosis, the treatment of choice is surgery with resection of all free margins. Since acinic cell carcinoma could be neglected, a high rate of recurrence after first resection have been reported. Low grade acinic cell carcinoma will be cured with surgery alone, but the site of origin indicates extension of resection. Superficial parotidectomy often effects complete removal of acinic cell carcinoma, but conservative parotidectomy is indicated if the deep lobe is involved. Initial approach would be more aggressive if the tumor is locally advanced acinic cell carcinoma, the facial nerve cannot be preserved, it must be resected and reconstructed with an autograft from greater auricular or sural nerve. Elective neck dissection is not recommended in acinic cell carcinoma, because of low risk of regional lymph node metastasis. However studies have revealed additional neck dissection decrease the rate of recurrence.

# Historical Perspective
Acinic cell carcinoma was discovered as a benign neoplasm until 1953.
All acinic cell carcinomas were classified as neoplasms in the WHO's international classification of disease for oncology by 1972. In a second edition, all acinic cell neoplasms considered as adenocarcinoma by 1990. Batsakis et al, described acinic cell carcinoma as a derivative from progenitor reserve cells of terminal tubules and intercalated ducts of salivary tissue for the first time.

# Pathophysiology
Acinic cell carcinoma, a salivary gland tumor, mainly develop in parotid gland (81000 out of 100000), less common. Acinic cell carcinoma occurs in the submandibular gland and minor salivary glands of palate. Acinic cell carcinoma belongs to the family of adenocarcinoma with similarities like: Adenoid cystic, Muco-epidermoid, low-grade adenocarcinoma, some breast cancers. The development of acinic cell carcinoma is the result of multiple genetic mutations that suggest association of tumor suppression genes such as: chromosome 5q, chromosome 6p, chromosome 17p, deletions of chromosome 6q, loss of chromosome Y, Trisomy 21, molecular studies suggest that retinoblastoma pathway also can be involved with acinic cell carcinoma.

# Differential diagnosis
Acinic cell carcinoma is a head and neck tumor happening in the salivary glands. If a patient was observed with related signs, the tumor must be classified as a benign or invasive by the capsule being intact. Differential diagnosis of a malignant tumor in the salivary gland is made after the incision and by histology features which will provide a good chemotherapy regimen for so-called patients.

# Epidemiology and demographics
In western countries, salivary gland carcinomas account for 4000 out of 100000 of all head and neck carcinomas, and approximately 80% of those occurring in parotid gland. One out of six parotid gland cancer is acinic cell carcinoma. Distribution of acinic cell carcinoma between age groups seems to be quiet even, with a median age of 52 years, but it occurs mostly at a younger age. Children are rarely affected with salivary gland carcinoma, but if they are it is most likely to be acinic cell carcinoma. Acinic cell carcinoma is predominantly seen in whites (85000 out of 100000 cases) and less in African nations(8000 out of 100000 cases)here is a higher incidence among female with the ratio ranging from 1.43:1 to 1.57:1.

# Risk factors
There is very little approved information about acinic cell carcinoma risk factors but familial predisposition and previous radiation exposure may play an important role.

# Screening
There is insufficient evidence to recommend routine screening for acinic cell carcinoma. Once diagnosis confirmed, ultrasonography, nuclear scans, CT scan and MRI can usually conduct for assessing the size of the tumor, location, and the nature of the tumor.

# Natural history, prognosis and complications
Parotid gland, is the most common site for acinic cell carcinoma affection. typically, acinic cell carcinoma is a slow-growing mass, lacking other symptoms. pain or fixation to surroundings is a sign of poor prognosis. nodal metastasis of acinic cell carcinoma is extremely rare. another rare complication is cranial nerve VII dysfunction. a small minority of acinic cell carcinoma occurs in sinonasal area or larynx. there is a big controversy about bilateral acinic cell carcinoma, it is still unknown if it invades bilateral glands or just a unilateral tumor. common sites for non-salivary acinic cell carcinoma is lacrimal gland, pancreas, and breast. Acinic cell carcinoma in the pancreas are so-called acinar cell carcinoma. the prognostic factors are age, pain, gender, race, previous inadequate treatment, the extent of disease, invasion of the skull base.

# Physical Examination
Physical examination of neck may reveal a firm swelling and tenderness.

# Staging
Clinical stage, particularly tumor size, maybe the critical factor to determine the outcome of salivary gland cancer and maybe more important than a histologic grade. TNM system is the system of choice for studying acinic cell carcinoma.

# Treatment
Acinic cell carcinoma is usually anatomically accessible tumor and patient do not show far metastasis at the time of diagnosis, the treatment of choice is surgery with resection of all free margins. Since acinic cell carcinoma could be neglected, a high rate of recurrence after first resection have been reported. low grade acinic cell carcinoma will be cured with surgery alone, but the site of origin indicates extension of resection. Superficial parotidectomy often effects complete removal of acinic cell carcinoma, but conservative parotidectomy is indicated if the deep lobe is involved. Initial approach would be more aggressive if the tumor is locally advanced acinic cell carcinoma, the facial nerve cannot be preserved, it must be resected and reconstructed with an autograft from greater auricular or sural nerve. Elective neck dissection is not recommended in acinic cell carcinoma, because of low risk of regional lymph node metastasis. However studies have revealed additional neck dissection decrease the rate of recurrence.

# Follow-up after treatment
Complications of surgical treatment for parotid neoplasms include facial nerve dysfunction and frey syndrome, also known as gustatory flushing or auriculotemporal syndrome. Frey syndrome has been successfully treated with injections of botulinum toxin A.