A Unique Diagnosis of Metastatic Prostate Adenocarcinoma

Abstract

Prostate adenocarcinoma is the most common non-skin cancer that affects men in the United States. Although its prevalence is high with 1/6 men being diagnosed with prostate cancer in their lives, the prognosis is often promising with only 1/36 men dying from prostate cancer. The prognosis of this cancer, like many, is based on the presence or absence of metastases. Gastroenterologists rarely encounter this malignancy as the primary is located in a genitourinary organ and the most common sites of metastasis are bone and lung, as well as local lymph nodes. However, there are rare cases when new or recurrent diagnoses of metastatic prostate cancer can be established via fine needle aspiration (FNA) of abnormal mediastinal lymph nodes under endoscopic ultrasound (EUS). An 80 year old man had a previous history of prostate adenocarcinoma that had been treated with radiation and adjuvant androgen deprivation therapy. About 18 months after completing treatment, steadily uptrending prostate serum antigen values prompted a PET scan. This showed increased uptake in multiple retroperitoneal lymph nodes, prompting a concern for metastasis. In addition, there were multiple mediastinal lymph nodes with increased uptake. Given the rare occurrence of mediastinal lymph node metastases in prostate malignancy, there was significant concern for a second malignancy. The patient underwent EUS to further evaluate (see image 1) and an FNA showed pathology consistent with prostate adenocarcinoma (see images 2 and 3). EUS FNA is a commonly used modality for concerning lymph nodes or masses noted on PET scans or other types of imaging. Similarly, prostate cancer is a common diagnosis, especially in elderly men. However, EUS FNA is very rarely used to confirm a diagnosis of metastatic prostate cancer. This case is unique because it highlights the potential for prostate adenocarcinoma to metastasize outside of its common sites of bone, lung, liver and retroperitoneal lymph nodes. It also illustrates the associated utility of EUS FNA. Case reports have described this method of diagnosis in only a select few cases. It is far more common for lymph node involvement above the diaphragm to be associated with lung, esophageal or head/neck cancers. Recognizing and sampling concerning mediastinal lymph nodes is vital to ensure that the correct primary malignancy is identified and appropriate chemotherapy or radiation regiments can be determined.2140_A Figure 1. EUS image showing an enlarged mediastinal lymph node (circled in red) prior to FNA.2140_B Figure 2. Papanicolaou stain showing a cohesive cluster of pleomorphic malignant cells (x200)2140_C Figure 3. Prostate specific antigen (PSA) immunohistochemical stain showing positive staining in the malignant cells, consistent with metastatic prostate adenocarcinoma (x200).