Non-Small Cell Lung Cancer With Synchronous Peritoneal Adenocarcinoma: A Rare Independent Combination

Lung cancer is one of the most common malignancies worldwide, and metastasis occurs in more than one-third of cases. Common sites of metastatic disease are the brain, spine, nerve, adrenal glands, bone, liver, and pleura. Peritoneal involvement, however, is rare, and peritoneal involvement found in lung cancer is presumed to be metastatic until proven otherwise. This is due to the fact that primary peritoneal adenocarcinoma is uncommon and difficult to distinguish from the metastatic spread.  Here, we report on a case of a 73-year-old woman who presented with ascites. Evaluation of ascitic fluid was consistent with adenocarcinoma. Subsequent CT of the chest revealed a 4.3-cm mass in the lower lobe of the left lung, which was determined to be poorly differentiated squamous cell carcinoma on histopathology. This is a rare case of two synchronous primary cancers: adenocarcinoma and poorly differentiated squamous cell carcinoma.  To conclude, physicians should be familiar with an independent presentation of squamous cell carcinoma of the lung and peritoneal carcinomatosis in the same patient, as the outcome of independent tumors is poor in most cases.