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Adipocytic Tumors

Adipocytic tumors represent an extremely heterogeneous category of clinically and morphologically distinctive lesions, sharing variable amounts of lipomatous differentiation. Some of them (i.e., benign lipomas and well-differentiated liposarcoma [WDLPS]) are among the most commonly encountered mesenchymal neoplasms. As will be discussed in depth, diagnostic criteria have been evolving constantly, in part because of the contribution of cytogenetics and molecular genetics. These techniques have not only offered…

Giant Cell–Rich Tumors

Multinucleated giant cells are seen in small numbers in a diverse range of soft tissue tumors. Similarly, soft tissue tumors with prominent giant cells compose a heterogeneous group of benign, intermediate, and malignant neoplasms. Recognition of the various types of morphologically distinct giant cells may provide clues to the diagnosis. In some cases, the giant cells instead distract the pathologist from paying careful attention to architectural…

Soft Tissue Tumors With Prominent Inflammatory Cells

Although a sparse lymphocytic infiltrate is relatively common in mesenchymal neoplasms, few histologic types of soft tissue tumors characteristically contain prominent inflammatory cells. In some such cases, the presence of an inflammatory infiltrate can be a diagnostic clue, whereas in other cases the infiltrate may obscure the neoplastic component and potentially lead to an erroneous diagnosis of either a reactive process or even a lymphoma. The…

Biphasic Tumors and Tumors With Mixed Patterns

Soft tissue tumors with biphasic histology are uncommon. The “biphasic” designation is often applied to tumors with mixed spindle cell and overtly epithelial (often glandular) components but can also be applied to tumors with mixed spindle cell and epithelioid morphology without epithelial differentiation. The classic example of a soft tissue tumor with such a pattern is biphasic synovial sarcoma, which, when arising at typical anatomic sites,…

Round Cell Tumors

The term small round blue cell tumors is used to refer to a group of generally highly aggressive malignant neoplasms, seen under the microscope as monotonous proliferations of small cells with scant cytoplasm. This category classically includes certain subtypes of sarcomas, carcinomas, lymphomas, melanoma, and neuroblastoma ( Box 8.1 ). Many of these tumor types are more common in young patients (e.g., small cell osteosarcoma), but…

Pleomorphic Sarcomas

Pleomorphic sarcomas are defined as malignant mesenchymal neoplasms characterized at a histologic level by prominent cellular pleomorphism and often brisk mitotic activity, with or without a readily identifiable line of differentiation. Cellular pleomorphism in mesenchymal neoplasms is probably best defined as a significant variation in the size and shape of individual cells within a lesion, primarily as a result of striking alterations in nuclear and cytoplasmic…

Epithelioid and Epithelial-Like Tumors

The group of epithelioid mesenchymal tumors encompasses neoplasms that are composed, partly or extensively, of rounded or polygonal cells, at least somewhat resembling epithelial cells ( Boxes 6.1 to 6.3 ). These tumors show variable, sometimes misleading growth patterns, including nested, sheetlike, strandlike, cordlike, or glandular-like architecture. In this chapter, only those tumors occurring in deep soft tissue and subcutis are examined in detail. Dermal lesions…

Tumors With Myxoid Stroma

Myxoid tumors of soft tissue are remarkable for their characteristic abundant extracellular matrix material. This heterogeneous group of lesions includes benign (and self-limited) tumors, those with a significant potential for local recurrence, and sarcomas. Because there is considerable clinical and histologic overlap, myxoid soft tissue tumors can pose problems in differential diagnosis. Immunohistochemistry is of limited help in distinguishing among the fibroblastic/myofibroblastic lesions in this group,…

Pediatric Spindle Cell Tumors

Spindle cell tumors in children and adolescents encompass a wide range of benign, intermediate, and malignant neoplasms, with the predominant phenotypic category being fibroblastic-myofibroblastic tumors. The most frequent spindle cell sarcomas of childhood include spindle cell and embryonal rhabdomyosarcoma (RMS), malignant peripheral nerve sheath tumor, synovial sarcoma, leiomyosarcoma, and various fibroblastic-myofibroblastic sarcomas. The majority of the nonrhabdomyosarcomatous spindle cell sarcomas occur more frequently in adults. In…

Spindle Cell Tumors of Adults

Numerous primary tumors and pseudotumors of soft tissues contain a variable number of spindle cells. In this chapter the authors will discuss only those lesions composed exclusively or predominantly of spindle cells that develop in adult patients and for which the spindle cell component is a key diagnostic feature. Some spindle cell tumors are discussed elsewhere in this book ( Table 3.1 ), if their clinical…

Biologic Potential, Grading, Staging, and Reporting of Sarcomas

Biologic Potential Among the most important reasons for the accurate classification of soft tissue tumors is the communication of clinical behavior (i.e., assignment into a managerial category). The vast majority of soft tissue tumors can be classified as either benign or malignant. Some benign tumors may occasionally recur, but they typically do so in a nondestructive fashion; simple surgical excision with narrow margins is generally adequate…

Introduction: Tumor Classification and Immunohistochemistry

Tumor Classification Soft tissue tumors have traditionally been classified according to line of differentiation—that is, which normal cell type the neoplastic cells most closely resemble. Such a “lineage” can often be assigned based on a combination of histologic appearances, patterns of protein expression (assessed by immunohistochemistry), and ultrastructural findings (identified by electron microscopy). Although electron microscopy once played an important role in the evolution of soft…

Malignant and borderline mesothelial tumors of the pleura

Mesothelioma Clinical findings in pleural mesothelioma The World Health Organization (WHO) defines mesothelioma as a malignant neoplasm arising from the mesothelial cells lining the body cavity surfaces and growing in a diffuse or, less commonly, localized invasive fashion. About 90% of mesotheliomas arise in the pleura, and over 30,000 new cases were reported at this location in 2018. The mean age of affected patients is 73,…

Benign and borderline tumors of the lungs and pleura

Lung cancer remains the leading cause of cancer death in the United States, with 236,000 new cases estimated annually and 130,180 estimated deaths (about 350 deaths per day). Benign and borderline malignant tumors of the lung are far outnumbered by their malignant counterparts and because of this less attention has been given to them. Nevertheless, because they often simulate malignant disease on imaging and are subject…

Pseudoneoplastic lesions of the lungs and pleural surfaces

There is a limited group of pulmonary lesions that one can classify as pseudoneoplastic, but their conditions constitute a significant aggregation in absolute numbers. Some are categorized as malformative or reactive, including pulmonary hamartomas (PHs); selected inflammatory pseudotumors (IPTs) (plasma cell granulomas); tumefactive lymphoid hyperplasias; inflammatory or reparative conditions simulating carcinomas; unusual granulomatous reactions; tumefactive pleural plaques; and florid examples of mesothelial hyperplasia. Other clinical pseudotumors…

Metastatic tumors in the lung: A practical approach to diagnosis

The most common pulmonary neoplasm is a metastasis from outside the lungs. Based on autopsy data, the lungs are involved by metastases in 25% to 55% of malignant diseases. In up to 25% of those cases, the pulmonary parenchyma and pleura are the only sites of distant spread. Because the majority of pulmonary metastases occur at a late stage and often are not sampled, the most…

Non-neuroendocrine carcinomas (excluding sarcomatoid carcinoma) and salivary gland-type tumors of the lung

Carcinoma of the lung is the second most common cancer worldwide (over 2 million new cases in 2020) and is the number one cause of cancer death, at 1.8 million worldwide in 2020. , Owing to this frequency, lung specimens, either for diagnosis, or obtained at resection, are common in the pathology laboratory. This chapter is divided into four sections. In the first section, general considerations…

Hematolymphoid disorders

The recent publications of the 4th edition of the World Health Organization (WHO) Classification of Tumors of the Haematopoietic and Lymphoid Tissues and the 5th Edition of the WHO Classification of Thoracic Tumors provide the most up to date diagnostic criteria for the diagnosis of thoracic lymphoid lesions and lymphoproliferative processes. The practice of hematopathology continues to lead the way in demonstrating the links between genotypic…

Sarcomas and sarcomatoid neoplasms of the lungs and pleural surfaces

Introduction Primary malignant pleuropulmonary tumors showing sarcomatoid features are exceedingly uncommon. Overwhelmingly, such lesions are epithelial in nature; neoplasms with a mesenchymal lineage in the lung and pleura are most often metastatic, arising from deep soft tissue sites or the female genital tract. In fact, because of the rarity of this category of pleuropulmonary malignancies, relatively few data exist in the literature regarding the morphologic or…