Soft Tissue Introduction Introduction and Overview Gross Examination Grading and Staging Ancillary Techniques Soft Tissue Immunohistochemistry Molecular Features of Soft Tissue Tumors Diagnostic Approach to Soft Tissue Tumors Overview Biopsy and Resection of Soft Tissue Tumors Clinical Approach Age- and Location-Based Approach to Diagnosis Histologic Approach Pattern-Based Approach to Diagnosis Feature-Based Approach to Diagnosis Tumors of Adipose Tissue Benign Lipoma Lipomatosis of Nerve Synovial Lipomatosis Angiolipoma Spindle Cell/Pleomorphic Lipoma Chondroid Lipoma Myolipoma Hibernoma Myelolipoma Lipoblastoma Intermediate, Locally Aggressive Atypical Lipomatous Tumor/Well-Differentiated Liposarcoma Atypical Spindle Cell Lipomatous Tumor Malignant Dedifferentiated Liposarcoma Myxoid Liposarcoma Pleomorphic Liposarcoma Fibroblastic/Myofibroblastic Lesions Benign Nodular Fasciitis Proliferative Fasciitis/Myositis Ischemic Fasciitis Myositis Ossificans Fibroosseous Pseudotumor of the Digit Fibroma of Tendon Sheath Desmoplastic Fibroblastoma Elastofibroma Angiofibroma of Soft Tissue Mammary-Type Myofibroblastoma Intranodal Palisaded Myofibroblastoma Superficial CD34(+) Fibroblastic Tumor Pleomorphic Fibroma Dermatomyofibroma Storiform Collagenoma Keloid Nuchal-Type Fibroma Intermediate (Locally Aggressive) Palmar/Plantar Fibromatosis Desmoid-Type Fibromatosis Intermediate (Rarely Metastasizing) Dermatofibrosarcoma Protuberans Solitary Fibrous Tumor Low-Grade Myofibroblastic Sarcoma Inflammatory Myofibroblastic Tumor Myxoinflammatory Fibroblastic Sarcoma Malignant Adult-Type Fibrosarcoma Myxofibrosarcoma Low-Grade Fibromyxoid Sarcoma Sclerosing Epithelioid Fibrosarcoma Pediatric Fibroblastic/Myofibroblastic Tumors Benign Fibrous Hamartoma of Infancy Calcifying Aponeurotic Fibroma Calcifying Fibrous Tumor Inclusion Body Fibromatosis Hyaline Fibromatosis Syndrome Fibromatosis Colli Gardner Fibroma Intermediate (Locally Aggressive) Lipofibromatosis Giant Cell Fibroblastoma Intermediate (Rarely Metastasizing) Infantile Fibrosarcoma Fibrohistiocytic, Histiocytic, and Dendritic Cell Tumors Benign Dermatofibroma and Fibrous Histiocytoma Deep Benign Fibrous Histiocytoma Localized-Type Tenosynovial Giant Cell Tumor Diffuse-Type Tenosynovial Giant Cell Tumor Cellular Neurothekeoma Xanthomas Solitary (Juvenile) Xanthogranuloma Reticulohistiocytoma Deep Granuloma Annulare Rheumatoid Nodule Langerhans Cell Histiocytosis Extranodal Rosai-Dorfman Disease Crystal-Storing Histiocytosis Intermediate (Rarely Metastasizing) Plexiform Fibrohistiocytic Tumor Giant Cell Tumor of Soft Tissue Malignant Histiocytic Sarcoma Follicular Dendritic Cell Sarcoma Interdigitating Dendritic Cell Sarcoma Smooth Muscle Tumors Benign Smooth Muscle Hamartoma Superficial Leiomyoma Deep Leiomyoma Intermediate Epstein-Barr Virus-Associated Smooth Muscle Tumor Malignant Leiomyosarcoma Pericytic (Perivascular) Tumors Benign Glomus Tumors (and Variants) Myopericytoma Myofibroma and Myofibromatosis Angioleiomyoma Tumors of Skeletal Muscle Benign Focal Myositis Adult Rhabdomyoma Fetal Rhabdomyoma Genital Rhabdomyoma Cardiac Rhabdomyoma Malignant Embryonal Rhabdomyosarcoma Alveolar Rhabdomyosarcoma Spindle Cell Rhabdomyosarcoma Sclerosing Rhabdomyosarcoma Pleomorphic Rhabdomyosarcoma Epithelioid Rhabdomyosarcoma Vascular Tumors (Including Lymphatics) Benign Papillary Endothelial Hyperplasia Bacillary Angiomatosis Congenital Hemangioma Infantile Hemangioma Lobular Capillary Hemangioma Epithelioid Hemangioma Spindle Cell Hemangioma Intramuscular Hemangioma Hobnail Hemangioma Acquired Tufted Angioma Microvenular Hemangioma Sinusoidal Hemangioma Glomeruloid Hemangioma Angiomatosis Lymphangioma Massive Localized Lymphedema Intermediate (Locally Aggressive) Kaposiform Hemangioendothelioma Intermediate (Rarely Metastasizing) Papillary Intralymphatic Angioendothelioma Retiform Hemangioendothelioma Composite Hemangioendothelioma Pseudomyogenic Hemangioendothelioma Atypical Vascular Lesion Malignant Epithelioid Hemangioendothelioma Angiosarcoma Kaposi Sarcoma Chondro-Osseous Tumors Benign Soft Tissue Chondroma Synovial Chondromatosis Malignant Extraskeletal Osteosarcoma Extraskeletal Mesenchymal Chondrosarcoma Peripheral Nerve Sheath Tumors Benign Solitary Circumscribed Neuroma Schwannoma Neurofibroma Perineurioma Hybrid Nerve Sheath Tumor Granular Cell Tumor Dermal Nerve Sheath Myxoma Ganglioneuroma Neuromuscular Choristoma Intermediate Melanotic Schwannoma Malignant Malignant Peripheral Nerve Sheath Tumor Epithelioid Malignant Peripheral Nerve Sheath Tumor Ectomesenchymoma Genital Stromal Tumors Fibroepithelial Stromal Polyp Angiomyofibroblastoma Cellular Angiofibroma Deep (Aggressive) Angiomyxoma Tumors of Mesothelial Cells Benign Adenomatoid Tumor Multicystic Peritoneal Mesothelioma Well-Differentiated Papillary Mesothelioma Malignant Malignant Mesothelioma Hematopoietic Tumors in Soft Tissue Solitary Extramedullary Plasmacytoma Myeloid Sarcoma Lymphoma of Soft Tissue Tumors of Uncertain Differentiation Benign Intramuscular Myxoma Juxtaarticular Myxoma Superficial Angiomyxoma Acral Fibromyxoma Pleomorphic Hyalinizing Angiectatic Tumor Aneurysmal Bone Cyst of Soft Tissue Ectopic Hamartomatous Thymoma Intermediate (Locally Aggressive) Hemosiderotic Fibrolipomatous Tumor Intermediate (Rarely Metastasizing) Atypical Fibroxanthoma Angiomatoid Fibrous Histiocytoma Ossifying Fibromyxoid Tumor Myoepithelioma of Soft Tissue Phosphaturic Mesenchymal Tumor Malignant Synovial Sarcoma Epithelioid Sarcoma Alveolar Soft Part Sarcoma Clear Cell Sarcoma Perivascular Epithelioid Cell Tumor (PEComa) Desmoplastic Small Round Cell Tumor Extraskeletal Ewing Sarcoma Extraskeletal Myxoid Chondrosarcoma Extrarenal Rhabdoid Tumor Intimal Sarcoma Undifferentiated/Unclassified Sarcomas Undifferentiated Pleomorphic Sarcoma Undifferentiated Round Cell Sarcoma With *CIC-DUX4* Translocation BCOR-CCNB3 (Ewing-Like) Sarcoma Mesenchymal Tumors of the Gastrointestinal Tract Benign Neural Gastrointestinal Polyps Gastrointestinal Stromal Tumor Gastrointestinal Schwannoma Gastrointestinal Smooth Muscle Neoplasms Inflammatory Fibroid Polyp Gangliocytic Paraganglioma Plexiform Fibromyxoma Malignant Gastrointestinal Neuroectodermal Tumor Other Entities Benign Amyloidoma Ganglion Cyst Tumoral Calcinosis Idiopathic Tumefactive Fibroinflammatory Lesions Cardiac Myxoma Cardiac Fibroma Congenital Granular Cell Epulis Nasopharyngeal Angiofibroma Sinonasal Glomangiopericytoma Ectopic Meningioma Glial Heterotopia Intermediate Paraganglioma Peripheral Hemangioblastoma Melanotic Neuroectodermal Tumor of Infancy Ependymoma of Soft Tissue Malignant Metastatic Tumors to Soft Tissue Sites Neuroblastoma and Ganglioneuroblastoma Extraaxial Soft Tissue Chordoma Undifferentiated Embryonal Sarcoma of the Liver Primary Pulmonary Myxoid Sarcoma Biphenotypic Sinonasal Sarcoma Spindle Epithelial Tumor With Thymus-Like Differentiation Low-Grade Endometrial Stromal Sarcoma.