Acinar cell carcinoma: Description, Causes and Risk Factors:
An adenocarcinoma arising from secreting cells of a racemose gland, particularly the salivary glands.
Racemose gland: A gland that has the appearance of a bunch of grapes if viewed as a three-dimensional reconstruction; e.g., a compound acinous or alveolar gland.
Acinar cell carcinoma is a rare aggressive tumor
that occurs predominantly in adults with a mean age of 62 years, but also represents about 15% of pancreatic neoplasms in children. A few patients develop a syndrome characterized by subcutaneous fat necrosis and polyarthralgia caused by excessive lipase in the serum secreted by this type of tumors. Because of their large size and relatively sharply circumscribed round to ovoid shape, acinar cell carcinoma can usually be distinguished from ductal carcinomas radiologically. Grossly cystic lesions are termed acinar cells carcinoma can usually be distinguished from ductal carcinoma radiologically.
Malignant acinar cells are deceptively bland and can resemble benign acinar cells. Conversely, normal acinar cells may be mistaken for acinar cell carcinoma. Unlike the malignant counterpart, normal acinar cells are organized into cohesive grape-like cluster on FNA (fine-needle aspiration) and don't display the high nuclear to cytoplasmic ratio or macronucleoli that are often noted in acinar cell carcinoma. In acinar cell carcinoma the relatively cohesive, organoid arrangement of benign acinar cells is replaced by cellular sheets and/or numerous single cells are stripped tumor nuclei. Tumor cells of acinar cells carcinoma are polygonal cells with round nuclei, coarse chromatin, prominent nucleoli and granular cytoplasm that may spill into the background. The absence of striking cytoplasmic granularity and large, prominent nucleoli are not rare, however, a situation that typically leads to diagnostic difficulty with other solid cellular neoplasms particularly Endocrine tumor.
Besides their characteristic histological features, acinar cell carcinomas are defined on the basis of their immunohistochemical staining for pancreatic enzymes, notably trypsin. There are few case reports on neoplasms with pancreatic acinar cell differentiation that occurred outside the pancreas, particularly in the gastrointestinal tract. Some of these cases were found in or next to heterotopic or metaplastic pancreatic tissue that was considered a possible source of the tumor. The occurrence of an acinar cell carcinoma as a primary liver neoplasm has been, so far, only once reported.
Symptoms are often non-specific and include weight loss
. A classical presentation includes subcutaneous nodules (due to fat necrosis) and arthralgias.
Diagnosis may include,
Cellular smears, solid cellular smear pattern.
- Loosely cohesive clusters and vague acini.
- Single cells, including stripped naked nuclei.
- Granular background of zymogen granules from stripped cytoplasm.
The primary neoplasm in the differential diagnosis of acinar cell carcinoma include the other parenchymal rich, stromal poor tumors of the pancreas-endocrine neoplasms, pancreatoblastoma and solid pseudopapillary neoplasm. All of these tumors can produce a very similar solid cellular, discohesive smear pattern of monomorphic polygonal cells. Pancreatoblastoma may be impossible to distinguish from acinar cell carcinoma based on cytology alone as acinar cell differentiation is the dominant-line of differentiation in this trilineage tumor and squamous corpuscles are impossible to appreciate on smears. Their distinction relies on individual cellular features and immunohistochemical stains. The primary ancillary tests include those that highlight the exocrine nature of the cells, PAS/dPAS histochemical stains and trypsin, chymotrypsin and lipase immunohistochemical stains.
Since normal pancreatic acinar cells secrete pancreatic enzymes, the most useful histochemical and/or immunohistochemical stains for acinar cell carcinoma are for the pancreatic enzymes, such as trypsin, chymotrypsin, amylase, elastase, and lipase. When the neoplastic cells exhibit nuclear polarity, these stains usually demonstrate positivity in the apical portions of the cells, while the stains are more focal and usually restricted to single cells in tumors with solid patterns. Tumor cells that are positive for synaptophysin and chromogranin A can be found in 30-50% of cases. Usually they occur in tumors with a solid pattern, where they are scattered throughout the tissue. Although only a small number of cases with synaptophysin immunohistochemistry have been reported, the diffuse positive staining for synaptophysin appears to be uncommon for acinar cell carcinoma and is a potential pitfall, thus emphasizing the need to perform the stains to demonstrate positivity for at least one pancreatic enzyme.
Acinar cell carcinomas are aggressive tumors and most patients die from their cancer within a mean of 18 months after diagnosis and a 5 year survival of 5.9%; however, the overall survival is better than pancreatic ductal adenocarcinoma. Younger patients (less than 60 years old) and patients with tumors less than 10 cm tend to have longer survival than patients over 60 years or with larger tumors. Patients who present with symptoms of elevated lipase do much worse (mean survival 8.8 months). Resection is the treatment of choice, with or without chemoradiation therapy, and metastases may be present at the time of diagnoses.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.