Acinar cell neoplasms arise from the acinar cells of the pancreas. Normal acinar cells are the primary cells of the exocrine pancreas and are responsible for secreting various enzymes. These tumors are distinct from the more common adenocarcinomas of the pancreatic ducts.
Because the tumors arise from normal acinar cells, the tumor cells also may secrete pancreatic enzymes, most commonly lipase. This is a rare cancer, accounting for only 1% of all pancreatic tumors, or approximately 400 cases per year in the U.S.
Risk Factors
There are few known risk factors for the development of acinar cell neoplasms. As with all pancreatic cancers, the risk increases with age, with an average age at diagnosis in the sixties. Smoking is the other important pancreatic cancer risk factor, but because acinar cell tumors are so rare, this association cannot be firmly established.
Signs and Symptoms
The most common initial presenting symptoms with these pancreatic neoplasms are abdominal pain, back pain and/or bloating. Diarrhea and weight loss are also commonly reported, and elevated liver enzymes and anemia are often present on blood tests. During a physical exam, patients frequently have a palpable abdominal mass and jaundice.
They may also have subcutaneous masses, which are a manifestation of excessive lipase secreted by the tumor cells. These masses should not be mistaken for metastatic disease and do not seem to portend a poorer prognosis when present.
Diagnosis and Staging
The diagnosis of ancinar cell tumor is made by biopsy of the pancreatic mass. A pathologist experienced in diagnosing pancreatic cancers should review the biopsy to confirm an acinar cell tumor versus the more common adenocarcinoma.
Once acinar cell cancer is established, patients should undergo an abdominal CT scan to verify the extent of disease, as well as a complete blood count and serum chemistries (including liver function tests and serum lipase).
Pancreatic cancer is staged as follows:
Stage I: Tumor is limited to the pancreas.
Stage II: Tumor extends beyond the pancreas but does not involve major nerves or arteries OR surrounding lymph nodes are involved with tumor.
Stage III: Tumor involves major nerves or arteries.
Stage IV: Metastatic disease is present.
About 50% of patients present with stage IV acinar cell cancer (metastatic disease) at the time of diagnosis. By far, the most common site of metastasis, as with all pancreatic tumors, is the liver.
Prognostic Factors
Because acinar cell tumors are so uncommon, there is little known about the long-term prognosis. From published case series, it appears that these tumors have a better prognosis than adenocarcinomas of the pancreas. The average survival appears to be 19 months, compared with only 6 months for adenocarcinomas. Patients with resectable disease (stage I or II only) generally survive an average of 3 years, whereas those with stage III or IV disease survive an average of 14 months.
Treatment
Acinar cell tumors are very rare and therefore cannot reasonably be studied in randomized, controlled clinical trials that compare treatments. Treatment decisions are therefore based upon published case series, and unfortunately, even those series describe limited numbers of patients.
Patients with localized tumors should undergo surgical resection if possible. This is the best treatment option for long-term survival. Patients who are good candidates for surgical resection are those without metastases and without major blood vessel involvement by the tumor. This seems to represent about half of patients at the time of diagnosis.
Most patients who have surgery, however, do eventually have recurrent disease. As such, clinicians may recommend adjuvant chemotherapy following surgery to try to prevent disease relapse.
Chemotherapy is commonly recommended for patients with unresectable or metastatic acinar cell cancer. No standard regimen exists. The drugs that appear to be most active against acinar cell tumors include fluorouracil (with leucovorin) and irinotecan. Gemcitabine has also been used with success in several case reports. These chemotherapy drugs are commonly used to treat more common pancreatic and colorectal cancers.
Radiation therapy has been reported as a treatment modality in several case reports as well, often given with concurrent fluorouracil. These patients did well and had either partial responses or sustained stable disease. Because there is no standard chemotherapy regimen for acinar cell neoplasms, patients should consider enrolling in a clinical trial of new chemotherapy or chemo-radiation strategies.
Supportive Care Issues
Infections due to chemotherapy immune suppression are common with drugs such as fluorouracil, gemcitabine, and irinotecan. Prophylaxis with antibiotics may be appropriate in some, and patients should always contact their oncologist if they develop a fever.
In addition to infections, fluorouracil and irinotecan also frequently cause diarrhea. This may be severe, leading to dehydration and electrolyte imbalances. Patients are often prescribed anti-diarrheal medications such as loperamide to decrease the severity of this complication. If diarrhea persists despite anti-diarrheal medications, patients should contact their oncologist promptly.
Pancreatic adenocarcinomas are known for causing moderate to severe chronic pain in a large proportion of patients. This may be the case for acinar cell neoplasms as well, especially if the celiac nerve is involved with tumor. Aggressive treatment of pain with opioid analgesics is standard of care for moderate to severe cancer pain, with doses individualized based upon concurrent disease states and patient response.
