Three Types of Spindle Cell Tumors of the Pleura

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Abstract
The clinicopathologic features of 17 fibrous tumors of the pleura are presented. Eight were benign localized fibrous tumors; all of these were negative when stained with antibodies to keratin. Eight were diffuse malignant tumors that demonstrated intense immunohistochemical staining of the spindle cells with antibodies to keratin. One case presented as a histologically malignant spindle cell tumor that was initially localized but recurred subpleurally three times in 12 years. This spindle cell tumor was consistently negative when stained for keratin. We conclude that there are three types of fibrous tumors of the pleura: (a) a localized, histologically benign, keratin-negative spindle cell tumor that might be termed “fibroma,” (b) a diffuse, histologically malignant, keratin-positive neoplasm that might appropriately be termed a “sarcomatoid mesothelioma,” and (c) a histologically malignant, keratin-negative, spindle cell tumor with the potential to spread under the pleura that might appropriately be termed a “sarcoma.” Immunohistochemistry proved to be useful in distinguishing the sarcomatoid mesothelioma from the sarcoma.