Retrospective analysis of unknown primary cancers with malignant pleural effusion at initial diagnosis

BACKGROUND Malignant pleural effusion (MPE) can occur during the progression of various cancers. However, factors, such as the incidence of MPE associated with different types of cancers and its potential for diagnosing previously undetected cancers, are unknown. Moreover, MPE may accompany potentially curable cancers or those with a favorable survival prognosis with adequate treatment. The present study determined the types of cancers accompanied by MPE at initial diagnosis and investigated appropriate related methods for diagnosing previously unknown cancers. METHODS We retrospectively reviewed the medical records of 35 patients with MPE at initial cancer diagnosis between 2004 and 2012. We evaluated the patient characteristics, final diagnosis, and diagnostic processes. RESULTS Of the 35 patients, 10 had lung cancer, seven ovarian or peritoneal cancer, four malignant pleural mesothelioma, one breast cancer, one lymphoma, one pancreatic cancer, and 11 had cancers of unknown origin. Diagnoses of the primary lesions were confirmed using the MPE cellblock method for seven of 11 patients (63.6%), by excisional biopsy or aspiration from other sites in four of nine patients, by exploratory laparotomy in two of three patients, and by peritoneal washing cytology in five patients. CONCLUSION Lung cancer and cancer of unknown origin are major causes of MPE at initial presentation. However, these groups also contain cancers that are curable and those with good long-term prognosis. The MPE cellblock method represents an accurate method for identifying cancer origin.