bubble_chart Overview

Acinic cell carcinoma, also known as serous cell adenocarcinoma, was not recognized as a type of salivary gland tumor before the 1950s. It was first systematically described and named by Foote and Frazell in 1953. Buxton confirmed its malignant nature, and the WHO designated it as acinic cell tumor, although its clinical manifestations often include recurrence and metastasis. Currently, it is mostly considered a low-grade malignant tumor. The tumor cells closely resemble the serous cells of the acini, leading to the belief that acinic cell carcinoma originates from acinar cells. However, the presence of intercalated duct cells in the lesions, along with transitions from intercalated duct cells to acinar cells, suggests that acinic cell carcinoma may arise from the intercalated duct epithelium.

bubble_chart Pathological Changes

(1) Gross Morphology The tumor is generally solitary, encapsulated, but the capsule is incomplete, and most have clear boundaries with surrounding tissues. It appears nodular or lobulated, with a firm texture. The cut surface is slightly convex, solid, grayish-white, with brownish-red spots, brittle, and lacks the moist and mucoid appearance of benign mixed tumors. Occasionally, cystic changes are observed, with the cysts containing brownish-red fluid.

(2) Microscopic Examination The tumor has a thin capsule, but tumor cell infiltration is often seen within the capsule. The tumor cells are arranged in solid clusters, forming structures resembling normal acini, trabeculae, tubules, or follicles, but without ducts or duct-like structures. Lobular or sheet-like structures may also be seen, with a small amount of stroma containing blood vessels and lymphoid tissue. Sometimes, solid or papillary cystic follicles are observed within the tumor. The tumor cells are round or polygonal, with small, eccentric nuclei, inconspicuous nucleoli, and abundant cytoplasm containing basophilic granules similar to the zymogen granules in normal acinar cells. However, some cells lack granules, and vacuoles may be seen within the cells. Some cells exhibit clear cytoplasm, and the presence of cells with distinct cytoplasm or vacuolated cells should be noted to differentiate from papillary cystadenoma, metastatic renal clear cell carcinoma, and mucoepidermoid carcinoma.

(3) Biological Characteristics Acinic cell carcinoma grows slowly and has a long clinical course, but it exhibits local infiltration and may recur and metastasize. Despite the uniformity and high differentiation of the tumor cells, it should not be considered benign and should always be regarded as low-grade malignant.

bubble_chart Clinical Manifestations

Acinic cell carcinoma is a relatively rare salivary gland tumor, accounting for 1-3% of all salivary gland tumors, 1-4% of major salivary gland tumors, and 5.1-12% of malignant salivary gland tumors. According to Garder's report, it constitutes 7-15% of malignant tumors in major salivary glands. The most common site of occurrence is the parotid gland, almost exclusively so. However, cases have also been reported in the submandibular gland, sublingual gland, and minor salivary glands. This tumor can occur from adolescence to old age, but is most frequently seen in individuals aged 40-60, with a higher incidence in females than males.

Clinically, acinic cell carcinoma resembles a mixed tumor, often presenting as a painless mass, occasionally with pain and symptoms of facial nerve involvement. The disease course is relatively long, ranging from several months to several decades. The tumor is typically round, solid, may have nodules, and is of medium or slightly firm consistency. A few cases exhibit cystic changes, are mobile, and not adherent to the skin. In advanced stages, metastasis can occur, with cervical lymph node metastasis being the most common.

bubble_chart Diagnosis

Due to the lack of characteristic clinical manifestations, even with specialized examinations such as sialography, CT, B-mode ultrasound, and radioactive isotope scanning, it is difficult to make an accurate preoperative diagnosis. A definitive diagnosis usually requires pathological examination.

bubble_chart Treatment Measures

The primary treatment is surgical resection. Due to the thin and often incomplete capsule of acinic cell carcinoma, and the frequent presence of small tumor nodules outside the capsule, wide excision is recommended. This includes subtotal resection with a margin of normal parotid tissue or total parotidectomy with preservation of the facial nerve, which is more appropriate. Whether to perform neck lymph node dissection should be determined based on clinical and histological types, and selective neck lymph node dissection is generally required.

Postoperative adjuvant therapy is usually unnecessary unless the lesion is extensive and there is suspicion of residual tumor, in which case radiotherapy may be considered. Since this tumor may metastasize distantly, some advocate for postoperative chemotherapy.

bubble_chart Prognosis

The recurrence rate of acinic cell carcinoma after surgery is 20-55%, with lymph node metastasis occurring in 3-11% of cases and distant metastasis in 10-12%. Although it has a tendency for metastasis and local infiltration, among salivary gland tumors, acinic cell carcinoma is relatively low in malignancy and generally has a favorable prognosis. The 5-year cure rate is consistently above 88%. Eneroth et al. reported 5-year and 15-year survival rates of 90% and 68%, respectively, while Spiro et al. reported 5-year, 10-year, and 15-year cure rates of 76%, 63%, and 55%, respectively, with a local recurrence rate of 33%. In China, Zhang Xiaoshan et al. reported 5-year, 10-year, and 15-year survival rates of 95.83%, 83.35%, and 60%, respectively, with a recurrence rate of 37.14%. The causes of tumor recurrence are multifaceted. For patients undergoing conservative tumor resection or enucleation, the local recurrence rate was 66.7%, with 22.2% of patients dying from tumor recurrence. In contrast, those who underwent total parotidectomy had a local recurrence rate of 9.5%.