Aims: We describe the clinicopathological characteristics of 15 cases of primary signet ring cell adenocarcinoma of the lung and highlight the importance of recognizing that not all adenocarcinomas with signet ring cell features represent metastatic adenocarcinomas.
Methods and results: We evaluated the clinicopathological and immunohistochemical features of 15 cases of signet ring cell adenocarcinoma of the lung. The patients were 12 men and three women, age 30-75 years (mean 52.5 years). No evidence of a primary tumour elsewhere could be found on thorough clinical examination. Nine patients underwent resection and the remainder were biopsied. The tumours ranged from 18 to 80 mm in greatest dimension. Microscopically, two distinct patterns of growth were recognized: acinar and diffuse. The tumours were characterized by the presence of >75% signet ring cells. Periodic acid-Schiff and mucicarmine showed strong intracellular positive staining. Immunohistochemical stains for TTF-1 (6/6) and CEA (9/9) showed strong positive reaction in all cases evaluated. Three out of six cases were also positive for cytokeratin 7. All the tumours (6/6) were negative for cytokeratin 20, ER, PR and GCDFP-15. Follow-up information was obtained in 11 patients; six patients died within 1 year and five patients were alive from 3 to 36 months after initial diagnosis.
Conclusion: These cases highlight an unusual histological growth pattern of primary lung adenocarcinoma that may be mistaken for a metastasis from an occult primary. The recognition of this pattern of lung tumours is important for proper treatment.