Synchronous Pulmonary and Cecal High-Grade Neuroendocrine Carcinomas Presenting as Hepatic Metastases: A Diagnostic Challenges and Literature Review.

Background and Clinical Significance: Neuroendocrine neoplasms (NENs) are a group of malignancies that may remain clinically silent for many years. The presence of hepatic metastases can be the first clue leading to diagnosis. Case Presentation: We report the case of a 67-year-old man with intermittent tiredness and suspicious hepatic nodules detected on routine abdominal ultrasound. Contrast-enhanced ultrasonography showed arterial hyperenhancement with early washout, suggestive of metastases. Synchronous high-grade neuroendocrine carcinomas (NECs) of the lung and cecum were identified. Although the liver lesions were initially presumed to arise from the cecal tumor, liver biopsy immunohistochemistry was TTF-1 positive/CDX2 negative, whereas the cecal lesion was TTF-1 negative/CDX2 positive. This mutually exclusive immunophenotype confirmed two separate primary carcinomas. Given the high-grade histology, the patient received platinum-based chemotherapy and achieved a partial response. Conclusions: This case illustrates the diagnostic complexity of synchronous lesions and highlights the "mirage of the first lesion" phenomenon, in which the initially detected tumor may not represent the true primary site. A comprehensive, multidisciplinary strategy is crucial for establishing the correct diagnosis and guiding optimal management.