S1734 Where's the Primary Site?

INTRODUCTION: Cancer of unknown primary site consist of around 5% of all malignancies. Initial workup frequently fails to detect the primary location. After light microscopic evaluation of a tissue biopsy, patients can be placed in one of four categories: neuroendocrine carcinoma, squamous cell carcinoma, adenocarcinomas, and poorly differentiated tumors. The diagnostic approach and treatment vary between these groups. We present a challenging case of liver metastasis with an unknown primary site in a patient with a past medical history of 2 primary malignant neoplasms. CASE DESCRIPTION/METHODS: An 86 y/o male with PMHX of alcohol abuse, tobacco use, thyroid cancer, and colon cancer presented to the ER with anorexia, dysphagia to solids, and 30lbs of unintentional weight loss for 6 months without any other symptoms. Chest CT revealed a 3 cm spiculated mass in the left upper lobe and multiple hepatic masses. Abdominopelvic CT revealed a nonspecific thickening of the duodenal bulb. Clinical findings suggested metastatic disease with an unknown primary site for which the gastroenterology service was consulted for a colonoscopy due to the patient’s history of colorectal cancer. Due to the patient’s advanced age and frail state, they recommended an interventional radiology consult for assessment of the patient’s liver lesions prior to scheduling a colonoscopy. Initial liver biopsy was positive for malignant cells and immunohistochemistry was positive for CK-7, CDX-2, CK19, Napsin A and TTF-1 and negative for CK 20 and Arginase 1, suggestive of primary lung adenocarcinoma with aberrant expression of CDX-2. DISCUSSION: This case presented a diagnostic challenge as the patient had a history of 2 primary neoplasms and workup showed 2 possible primary sites, lung versus gastrointestinal tract. Initial workup for metastatic cancer’s primary site must include a comprehensive medical history and a thorough physical exam, along with laboratory studies like basic chemistries, complete blood count, and imaging studies of the abdomen, pelvis, and chest. Pelvic examination and mammography might be warranted in female patients, whereas PSA and prostate exam should be considered in male patients. Appropriate tissue biopsy results help determine subsequent testing in order to establish the primary site and specific treatment. In this case, liver biopsy played a key role in the proper identification of the primary site and in avoiding unnecessary invasive workup such as endoscopic procedures in this frail elderly patient.Figure 1.: Chest CT with contrast showed 3 cm spiculated mass in the left upper lobe.Figure 2.: Non-specific thickening of the duodenal bulb showed in abdominal and pelvic CT.Figure 3.: Liver mass shown in CT scan suggesting metastatic disease.