Metastatic prostatic adenocarcinoma.
This case illustrates the importance of documentation of proper clinical history in pathology. The pancreatic head mass FNA and bile duct biopsy specimens were compatible with involvement by an adenocarcinoma that was CK19 positive. Considering the radiographic and pathologic findings, the biopsies were highly suspicious for a primary pancreatic adenocarcinoma. Nonetheless, the presence of prominent macronucleoli, which is not a feature commonly seen in pancreatic adenocarcinoma, prompted for further characterization of this pancreatic neoplasm. The differential diagnoses that were considered included other pancreatic neoplasms, such as, acinar cell carcinoma, neuroendocrine tumor/carcinoma and a metastasis.
Knowledge of the patient's remote history of prostatic carcinoma (by report only, slides were not available for review) and the unusual cytologic/histologic features, prompted us to perform a panel of immunohistochemical stains that were consistent with a metastasis from the patient's known prostate cancer. The diagnosis heavily relied on the immunoreactivity for NKX3.1, PSA and androgen receptor. Other diagnoses were excluded by the lack of immunostaining for trypsin (acinar cell carcinoma), S100 protein and tyrosinase (metastatic melanoma), and synaptophysin (neuroendocrine tumor/carcinoma).
It is well known that primary neoplasms of the pancreas are far more common than metastatic tumors. In the literature, metastases to the pancreas comprise approximately 2%-4% of pancreatic tumors (1-2). Importantly, autopsy data demonstrate that metastases to the pancreas are common in those cases with diffuse spread of primary cancer to multiple organs, but exceedingly rare as an isolated metastatic lesion (4). The most common primary tumors reported to metastasize to the pancreas include renal cell, gastrointestinal (colon and stomach), breast and lung carcinomas, melanomas and some sarcomas (4-5). Unfortunately, metastases to the pancreas often occur as solitary masses in the head of the pancreas in patients without history of malignancy, thus resembling a pancreatic primary. Additionally, in many cases and as seen herein, the radiologic impression is also that of a primary tumor; however, treatment options and prognosis are significantly different. This underscores the importance of proper clinical history.
Metastatic prostatic adenocarcinoma to the pancreas is a rare presentation, and has been reported as isolated case reports in the English literature. EUS-FNA is the preferred method to assess these tumors (6-7). To arrive at the correct diagnosis, not only is knowledge of the clinical history important, but a panel of immunohistochemical stains is imperative. These include PSA, PSMA, androgen receptor and the recently described NKX3.1. NKX3.1 has a high sensitivity and specificity for prostatic origin with the benefit of being a nuclear stain that is not affected by anti-androgen therapy (8).
Given the increasing use of EUS-FNA of pancreatic masses, the lack of literature on this topic and the large spectrum of metastasis that can be seen in the pancreas, it is important for the practicing pathologist to recognize this potential pitfall.
Contributed by Humberto Trejo Bittar, MD. Sheldon Bastacky, MD and Aatur D. Singhi, MD, PhD.