Peritoneal neuroendocrine carcinoma of unknown primary with markedly elevated alpha-fetoprotein: a case report

Peritoneal neuroendocrine carcinoma(NEC) is primarily metastatic, with primary cases being exceedingly rare. The relationship between alpha-fetoprotein(AFP) and neuroendocrine carcinoma remains unclear. In this report, we present a patient with peritoneal neuroendocrine carcinoma who exhibited significantly elevated AFP levels. Extensive evaluation revealed no obvious primary site outside the peritoneum; however, occult gastrointestinal origin could not be entirely excluded. The tumor was thus classified as NEC of unknown primary, with a presumed primary peritoneal origin. The findings from this case suggest that markedly elevated AFP may be associated with aggressive tumor behavior and could serve as a potential marker for monitoring disease activity in peritoneal NECs, a hypothesis that warrants further investigation.

A 51-year-old man with massive ascites and elevated AFP levels was admitted to the hospital. Liver enhanced magnetic resonance imaging and gastrointestinal endoscopy did not reveal any space-occupying lesions, while abdominal puncture did not detect tumor cells. The patient's whole-body PET-CT revealed extensive peritoneal thickening and increased FDG metabolism. Subsequent laparoscopic exploration revealed numerous nodules and masses of varying sizes with a firm texture in the greater omentum, small intestine surface, mesentery, and parietal peritoneum. Immunohistochemistry of the omentum demonstrated positive results for AE1/AE3, Syn, CgA, and AFP, leading to a final diagnosis of large cell NEC of unknown primary, with a presumed primary peritoneal origin. Due to the presence of multiple peritoneal nodules, radical surgery was not feasible, and EP combined with camrelizumab was initiated. AFP levels showed an overall progressive increase, peaking at 5315 ng/mL on May 25, with a slight subsequent decline to 4948.4 ng/mL on June 20. Unfortunately, the patient discontinued chemotherapy after two cycles due to severe nausea and vomiting; he subsequently succumbed to the disease.

We propose the hypothesis that dynamic changes in AFP levels could reflect tumor burden and treatment response in a subset of AFP-producing NECs. However, this hypothesis requires validation in larger cohort studies. It is also important to distinguish its potential role as a monitoring biomarker from an established prognostic biomarker.