Pericardial and Pleural Metastases: Clinical, Histologic, and Molecular Differences.

BACKGROUND: Pericardial and pleural cavities produce effusions with important clinical consequences. Metastases are one of the most common etiologies of both serosal effusions. However, data regarding the type of metastatic involvement of the pleura and the pericardium are lacking. This study investigated the histologic patterns of tumors involving the two cavities to better define their pathophysiology and possible consequences in molecular diagnostics.

METHODS: This was a retrospective study of patients diagnosed with pericardial (n = 75) and pleural (n = 70) metastases. Patterns of metastasis were characterized as (1) tumor cells floating inside the cavity (2) as lymphatic emboli and (3) as tumor cells frankly invading underlying fibrous tissue. Molecular analysis (EGFR, KRAS, BRAF, ALK, HER2) was performed in 44 metastases of lung adenocarcinomas.

RESULTS: The two serosal membranes differed significantly (p < 0.0001) in the pattern of metastasis. The pleura showed predominantly an invasive pattern (67 [95.7%]), whereas most pericardial metastases consisted of tumor cells floating inside the cavity or as lymphatic emboli (44 [58.6%]). The origin of the primary differed marginally between the two organs. Time to diagnosis of metastasis differed between the two organs, with pleural metastases presenting later than the pericardial ones. Molecular analysis failed more often in pericardial biopsy specimens and in specimens with emboli or surface involvement.

CONCLUSIONS: Although pericardium and pleura share common embryologic and histologic features and are often regarded as giving similar effusions, they differ significantly in the type of metastases involving them. This can have important consequences in histologic, cytologic, and molecular diagnostics.