Paraneoplastic Hypercholesterolemia Identified in an Adult Male Diagnosed With Metastatic Yolk Sac Tumor

A few cases of paraneoplastic hypercholesterolemia have been reported in patients with primary or metastatic liver cancer. We report a case of paraneoplastic hypercholesterolemia in a patient with a metastatic yolk sack tumor. The patient was a 52-year-old man who presented with abdominal pain, nausea, and vomiting. A computed tomography (CT) scan demonstrated massive hepatomegaly with innumerable large ill-defined hypo-densities and innumerable pulmonary nodules. Blood work demonstrated elevated bilirubin to 3.1 mg/dL, aspartate aminotransferase (AST) to 384 U/L, alanine aminotransferase (ALT) to 126 U/L, gamma-glutamyl transferase (GGT) to 574 U/L, lipase to 100 U/L, low-density lipoprotein (LDL) of 579 mg/dL, and cholesterol of >800 mg/dL. Tumor markers revealed alpha-fetoprotein (AFP) was 24,760 ng/mL, carcinoembryonic antigen (CEA) was 1.9 ng/mL, and cancer antigen 19-9 (CA19-9) was 86 U/mL. The tumor makers were obtained during the initial stages of the patient’s evaluation to help us narrow down the possible primary - focusing on the gastrointestinal tract and the pancreas. Although tumor markers are rarely of use in the early diagnosis of cancer due to their limited sensitivity and specificity; however, they can help diagnose the origin of cancer in patients presenting with advanced widespread disease such as our patient. Histopathology of his liver lesion biopsy demonstrated a metastatic yolk sac tumor (YST) with hepatoid differentiation. Since the patient succumbed rapidly, the primary tumor could not be ascertained, although the lack of a classic pattern for testicular tumor retroperitoneal lymphadenopathy makes extragonadal YST more likely. YSTs are major histologic subtypes of germ cell tumors (GCTs), and most frequently arise in the gonads. However, extragonadal GCT is sometimes seen and comprises about 2-5% of all GCTs in adult males aged 15-35 years. Extra gonadal GCT has been hypothesized to occur through aberrant migration of primordial germ cells or reverse migration of transformed germ cells from the testes, and persistence of pluripotent cells outside the gonads. Paraneoplastic syndromes associated with GCTs are rare. The pathophysiology of paraneoplastic hypercholesterolemia is hypothesized to involve the dysregulation of LDL receptors. Cancer-mediated mutations in the LDL receptor gene result in an abnormal LDL receptor, leading to autonomous cholesterol production by neoplastic cells. Also, tumor-secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) has been implicated in the causation of paraneoplastic hypercholesterolemia. PCSK9 binds to and degrades the receptor for LDL particles on cell membranes. YST in adults is exceedingly rare. Paraneoplastic hypercholesterinemia is a very rare phenomenon reported in different cancers and we report the first case associated with YST.