Pulmonary adenocarcinoma with microcystic histology and intratumoral heterogeneity of EGFR gene polymorphism.

Aims: To study the clinicopathological features of pulmonary adenocarcinomas with microcystic histology.
Materials and Results: Two cases of pulmonary adenocarcinoma exhibiting a unique microcystic growth pattern were analysed. The 20-mm tumour of a 59-year-old woman showed a predominantly complex microcystic architecture with a focal papillary configuration, whereas the 15-mm tumour of another 46-year-old woman displayed a solely microcystic growth pattern. The first tumour was found to have metastasized to lymph nodes at surgery and, 4 years later, to the chest wall. The second tumour did not metastasize or recur over a follow-up period of 12 years. The tumour cells were immunoreactive with thyroid transcription factor-1 (TTF-1), which helped to differentiate them from salivary gland-type tumours. No mutations of epidermal growth factor receptor (EGFR) or K-ras genes were detected. However, facilitated by laser microdissection, a Q787Q polymorphism was found in the microcystic component but not in the papillary component. To our knowledge, this is the first report to illustrate intratumoral heterogeneity of EGFR gene polymorphism among different growth patterns within the same tumour.
Conclusions: Pulmonary microcystic adenocarcinoma has a variable clinical outcome. The microcystic tumour cells are immunoreactive with TTF-1 and may harbour polymorphisms of the EGFR gene.