Cytological features of lung adenocarcinoma with micropapillary pattern in the pleural or pericardial effusion: analysis of 5 cases.

Micropapillary pattern is a distinct histopathological pattern, and usually shows a high frequency of lymphatic invasion and lymph node metastases. This pattern is also reported in lung adenocarcinoma, however, only one cytological report of lung adenocarcinoma with micropapillary pattern has been reported. In this study, we analyzed the cytological features of this type of carcinoma in the pleural or pericardial effusion. This study was comprised of 5 consecutive cases of lung adenocarcinoma with micropapillary pattern, in which the tumor cells were present in the pleural or pericardial effusion and whose diagnoses were histopathologically confirmed. The characteristic cytological findings in the pleural or pericardial effusion were as follows: i) tightly cohesive small nests of tumor cells showing papillary structure without fibrovascular core, ii) these nests were comprised of approximately 5-20 tumor cells, iii) cauliflower-like and acinar-like structures were also observed, iv) intracytoplasmic vacuoles were observed in 40% of the cases, and v) the neoplastic cells had large round to oval nuclei containing coarse chromatin and occasional conspicuous nucleoli. It has been reported that the presence of micropapillary structure and intracytoplasmic vacuolation are also characteristic cytological features of micropapillary carcinoma of the urinary bladder, therefore, they are thought to be common cytological features of carcinomas with micropapillary pattern. Consequently, detection of these features can lead to a cytodiagnosis of lung adenocarcinoma with micropapillary pattern in the pleural or pericardial effusion. Recognition of these features is important because this type of tumor shows an aggressive clinical course.