Malignant pleural neoplasm with both differentiation of epithelioid mesothelioma and squamous-cell carcinoma, a rare phenomena.

Malignant mesothelioma, a neoplasm arising within the serosal surfaces, has been linked closely to asbestos exposure. We present a case of 72-year-old male with a 27 year work-related history of asbestos exposure who presented with dyspnea. Chest computed tomography scan showed a large, right pleural effusion with compressive right lung atelectasis. Biopsies, subsequent pleurectomy and lung wedge resections revealed epithelioid malignant mesothelioma with associated focal non-keratinizing squamous-cell carcinoma, supported by extensive immunohistochemical stains and molecular studies. The patient was treated with 6 cycles of carboplatin/pemetrexed, showing no new metastases. Seven months post-treatment, the patient presented with progressive dyspnea and large pleural effusions. Bilateral pleural fluid was collected and showed malignant epithelioid cells, morphologically similar to the patient's pleural neoplastic cells. However, the tumor was positive for squamous cells markers and showed BAP1 loss, while negative for mesothelial markers. The findings support the diagnosis of squamous-cell carcinoma and were consistent with the patient's previously diagnosed pleural neoplastic origin. A malignant mesothelioma associated with squamous-cell carcinoma is a rare phenonmenon. To our knowledge, only two case reports are available in current literature. This unique case shows a single pleura tumor differentiating as both malignant mesothelioma and squamous-cell carcinoma. Squamous-cell carcinoma is the predominating malignancy seen within the bilateral pleural effusions, a potential pitfall for cytology specimen diagnosis.