Can anyone help me code " Stage IV pulmonary vs. extra pulmonary small cell carcinoma from ascitic fluid" Pathology states metastatic small cell undifferentiated neuroendocrine carcinoma. The tumor possible primary site, however, cannot be accurately predicted based on this evaluation alone. Possible primary sites include gynecological tract, gastrointestinal tract, pancreatic and lung tumors. Clinicopathological correlation and followup suggested. Would this be a 199.1 until we get something more determinate?