Primary signet ring cell carcinoma of the lung: A case report

Signet ring cell carcinoma (SRCC) of the lung is a rare variant of pulmonary adenocarcinoma. Because the majority of SRCCs in the lung are metastatic tumors from stomach, colon, or breast. The differential diagnosis of primary SRCC from metastatic SRCC is important but may be problematic. Recently, immunohistochemical studies are known to be valuable in determining primary sites of SRCC. Herein, we present a case of primary signet ring cell carcinoma of the lung in a 67-year-old man. Even though radiographic findings of our case were more suggestive of metastatic orgin of SRCC in the lung, we could finally conclude that lung was the primary site of SRCC with the help of immunohistochemical studies (positive TTF-1 and CK7, and negative CK 20) and other diagnostic work up.