Malignant mesothelioma with prominent adenomatoid features: a clinicopathologic and immunohistochemical study of 10 cases.

The clinicopathologic and immunohistochemical features of 10 cases of pleural malignant mesothelioma with predominantly adenomatoid growth pattern are described to determine the clinical, histologic, and behavioral features of these tumors and to highlight the importance of separating this unusual pattern from the benign adenomatoid tumor. Seventy-seven cases of pleural biopsy and extrapleural pneumonectomy specimens for malignant mesothelioma were examined to identify the specific type of histologic growth pattern exhibited by the tumors. The 10 cases herein described were identified as an unusual histopathologic subset of these tumors. Nine patients were men and one was a woman with an age range of 56 to 82 years (mean, 68.5 years). The main presenting symptoms included cough, dyspnea, and chest pain. The typical features of pleural malignant mesothelioma were noted both radiologically and macroscopically. The tumors were characterized by diffuse pleural thickening with confluent nodular patches of tumor obliterating the pleural space. Histologically, a distinct morphology was observed composed of small tubular spaces lined by epithelioid cells, reminiscent of adenomatoid tumors of the genital tract. Immunohistochemical studies confirmed the mesothelial nature of the tumors. Clinical follow-up in 7 of 7 patients demonstrated a mean survival of 10 months from time of diagnosis. Adenomatoid mesothelioma is an unusual variant of epithelioid malignant mesothelioma that histologically may mimic a range of other tumors, including benign adenomatoid tumors and metastases of adenocarcinoma to the pleura. The clinical presentation, infiltrative growth, distinct histologic features, cytologic atypia and immunohistochemical profile all serve to differentiate adenomatoid malignant mesothelioma from other infiltrative processes involving the pleura.