80 year old man with pleural effusion

80 year old man  with pleural effusion...remarkable case I struggled with for about 2 weeks.

This is an 80-year-old man who comes to the ER complaining of chest pain and difficulty breathing.  Myocardial infarction was ruled out and during routine workup he was found to have a right-sided pleural effusion.  The patient is a former smoker and has a history of asbestos exposure.  The pleural effusion was taped and was sent for cytology. X-ray performed after the tap showed right pleural plaque.  Additionally CT scan with contrast was performed which confirmed the existence of right pleural plaque measuring 5 x 3 cm and pleural effusion. There were no pulmonary masses or nodules.

View the case.

Discussion

The cytology of the pleural effusion was highly cellular composed of numerous of what appear to be mesothelial cells arranged in clusters and singly.  In the background observed also were chronic inflammatory cells and blood.  Upon closer examination mesothelial windows were identified however the cells which are arranged in clusters showed marked nuclear pleomorphism and nuclear membrane irregularities.  Necrosis apoptosis and mitotic figures were not seem. Cell block also showed numerous cells in different sizes and shapes some with nuclear membrane irregularities, increased NC ratios and some degenerative changes. the immunohistochemistry performed on the cell block shows a mixture of Calretinin positive mesothelial cells as well as BerEP 4 positive cells.  Mucicarmine and PAS D stains were also positive. Based on this finding the diagnosis of positive for malignant cells, adenocarcinoma was rendered. When the case was discussed with clinicians the main question was the primary source of the adenocarcinoma.  The patient had extensive workup with a CT scan and MRIs however primary tumor was not found.  the decision was made to remove the pleural plaque and do pleurodesis to prevent further effusions. The pleural plaque was sent for histology.

Histology:

the H. and E. examination of the pleural plaque reveals fibrous pleural plaque with marked chronic inflammation and what appears to be  a papilary mesothelial hyperplasia as well as foci of displaced mesothelium. Examination of these foci of displaced mesothelium reveal that the cells show similar characteristics as the one observed in the cytology specimen.
 

Immunohistochemical analysis reveals that the cells are: 

EMA+, BerEp4 +, CEA+, CK7+, CK20-, TTF-1 +, Mucicarmin +, D-PAS positive.

Based on this finidngs what would be the most appropriate interprepation providing that the patient has no lung masses ?