Surgical Pathology Clinics

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Atypical spindle cell/pleomorphic lipomatous tumor (ASCPLT) is a rare soft tissue neoplasm, commonly arising in the subcutis (more common than deep soft tissue) of limbs and limb girdles during mid-adulthood. ASCPLT is histologically a lipogenic neoplasm with ill-defined margins composed of a variable amount of spindle to pleomorphic/multinucleated cells within a fibromyxoid stroma. ASCPLTs lack MDM2 amplification, but a large subset show RB1 deletion and variable expression of CD34. Though initially thought to be the malignant form of spindle cell lipoma, ASCPLTs are benign with local recurrences (∼10-15%) and no well-documented dedifferentiation or metastasis...

MIFS is a low-grade fibroblastic sarcoma that predilects to superficial distal extremity soft tissue. It is composed of plump spindled and epithelioid cells, inflammatory infiltrates, and mucin deposits in a fibrosclerotic stroma. Large epithelioid cells harboring bizarre nuclei and virocyte-like macronucleoli and pleomorphic pseudolipoblasts are characteristic. While conventional MIFS has locally recurrent potential but minimal metastatic risk, tumors with high-grade histologic features have a greater risk for recurrence and metastasis...

Calcified chondroid mesenchymal neoplasms (CCMN) represent a morphologic spectrum of related tumors. Historically, chondroid matrix or chondroblastoma-like features have been described in soft tissue chondroma, tenosynovial giant cell tumors (especially of the temporomandibular joint (TMJ) region), and in a subset of tophaceous pseudogout. Recently, these tumors have been found to share FN1-receptor tyrosine kinase (RTK) fusions. This review discusses the clinical, morphologic, immunohistochemical, and molecular genetic features of CCMN...

Inflammatory rhabdomyoblastic tumor is a recently introduced name for neoplasms currently included in the World Health Organization classification of soft tissue tumors under the rubric inflammatory leiomyosarcoma. Inflammatory rhabdomyoblastic tumor is an excellent example of how surgical pathologists working in conjunction with tumor biologists can greatly improve tumor classification to the benefit of patients. Over the last 28 years, understanding of this entity has undergone a fascinating evolution...

Xanthogranulomatous epithelial tumor is a recently described soft tissue tumor characterized by subcutaneous location, partial encapsulation, a xanthogranulomatous inflammatory cell infiltrate, and keratin-positive mononuclear cells. It shares some morphologic features with keratin-positive, giant cell-rich soft tissue tumors. Both have recently been shown to harbor HMGA2::NCOR2 fusions. The relationship between these tumors and their differential diagnosis with other osteoclast-containing soft tissue tumors is discussed...

The wide application of increasingly advanced molecular studies in routine clinical practice has allowed a detailed, albeit still incomplete, genetic subclassification of undifferentiated round cell sarcomas. The WHO classification continues to include provisional molecular entities, whose clinicopathologic features are in the early stages of evolution. This review focuses on the clinicopathologic, molecular, and prognostic features of undifferentiated round cell sarcomas with EWSR1/FUS::NFATC2 or EWSR1::PATZ1 fusions...

Myxoid pleomorphic liposarcoma (MPLPS) shows a strong predilection for the mediastinum and can affect a wide age range. Clinically, MPLPS exhibits aggressive behavior and demonstrates a worse overall and progression-free survival than myxoid/round cell liposarcoma (MRLPS) and pleomorphic liposarcoma (PLPS). Histologically, MPLPS is characterized by hybrid morphologic features of MRLPS and PLPS, including myxoid stroma, chicken wire-like vasculature, univacuolated and multivacuolated lipoblasts, and high-grade pleomorphic sarcomatous components...

Pleomorphic dermal sarcoma (PDS) is a rare cutaneous/subcutaneous neoplasm of purported mesenchymal differentiation that exists along a clinicopathologic spectrum with atypical fibroxanthoma (AFX). While PDS and AFX share histopathologic and immunohistochemical features, PDS exhibits deeper tissue invasion and has a higher rate of metastasis and local recurrence than AFX. Given its aggressive clinical course, early recognition and clinical management of PDS are essential for optimizing patient outcomes. This review aims to provide a brief overview of the clinicopathologic and molecular features, prognosis, and treatment of PDS...

CIC-rearranged sarcoma is a rare type of small round cell sarcoma. The tumors often affect the deep soft tissues of patients in a wide age range. They are highly aggressive, respond poorly to chemotherapy, and have a worse outcome than Ewing sarcoma. CIC-rearranged sarcoma has characteristic and recognizable histology, including lobulated growth, focal myxoid changes, round to epithelioid cells, and minimal variation of nuclear size and shape. Nuclear ETV4 and WT1 expression are useful immunohistochemical findings...

GLI1-altered mesenchymal tumors comprise an emerging group of neoplasms characterized by fusions or amplifications involving GLI1, a gene that encodes a key regulator of the Hedgehog signaling pathway. In recent years, tumors with GLI1 alterations have been reported across a variety of anatomic sites and a broad age range. Although these tumors can exhibit a wide morphologic spectrum and a variable immunophenotype, they frequently present with monomorphic ovoid cells arranged in distinctive nests with a rich, arborizing vascular network...

Sclerosing epithelioid fibrosarcoma (SEF) is a distinctive sarcoma that may arise in nearly any soft tissue site or bone. While there has been past controversy as to whether it is related to low-grade fibromyxoid sarcoma (LGFMS), it has been shown to behave far more aggressively than LGFMS. SEF has a propensity to metastasize to the lungs and bone and arise within the abdominal cavity. Histologically, it is characterized by uniform nuclei embedded in a densely collagenous stroma simulating osteoid. By immunohistochemistry, it is often strongly positive for MUC4...

Perivascular epithelioid cell tumors (PEComas) are a heterogenous group of mesenchymal neoplasms with a mixed myomelanocytic immunophenotype. PEComa-family tumors include angiomyolipoma, lymphangioleiomyomatosis, and a large category of rare neoplasms throughout the body that are now classified under the umbrella term "PEComa." This review focuses on recent advances in the clinicopathological and molecular features of PEComas, with an emphasis on PEComas that originate in soft tissue.

Superficial CD34-positive fibroblastic tumor is a mesenchymal neoplasm of "intermediate malignancy" recently included in the fifth edition of the World Health Organization classification of soft tissue and bone tumors. In this review, we summarize the current knowledge on this rare entity with a special focus on its clinicopathological features, morphologic spectrum, and differential diagnosis. We also provide data regarding recent discoveries on its molecular profile and discuss its prognosis and management...

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Infectious diseases of the GI tract mimic a variety of other GI diseases, including chronic idiopathic inflammatory bowel disease and ischemia. It can be challenging to identify pathogens in tissue sections as well, as many trainees are not exposed to infectious disease pathology other than in the context of microbiology. Our ability to diagnose infections in formalin fixed, paraffin embedded material has grown exponentially with the advent of new histochemical and immunohistochemical stains, as well as more options for molecular testing...

Small round cell neoplasms are diagnostically challenging owing to their clinical and pathologic overlap, necessitating use of large immunopanels and molecular analysis. Ewing sarcomas (ES) are the most common, but EWSR1 is translocated in several diverse neoplasms, some with round cell morphology. Molecular advances enable classification of many tumors previously termed 'atypical ES'. The current WHO Classification includes two new undifferentiated round cell sarcomas (with CIC or BCOR alterations), and a group of sarcomas in which EWSR1 partners with non-Ewing family transcription factor genes...

Pathologists are increasingly asked to evaluate mast cell infiltrates in the gastrointestinal tract when there is clinical concern for systemic mastocytosis or a variety of functional disorders, including irritable bowel syndrome and mast cell activation syndrome. Neoplastic mast cells have established quantitative, morphologic, and immunohistochemical features that facilitate their identification in gastrointestinal mucosal biopsies. Specific qualitative and quantitative findings are lacking for inflammatory mast cell-mediated disorders...

Graft-versus-host disease (GVHD) is a major complication of hematopoietic stem cell transplantation (SCT), leading to a significant morbidity and mortality. Histologically, gastrointestinal GVHD is characterized by crypt apoptosis and dropout. However, similar histologic features can also be seen in drug-induced injury and opportunistic infection. Knowledge of the timing of biopsy, patient medications, evidence of infection, and presence of GVHD at other organ sites can aid in the correct diagnosis and subsequent management of these patients...

Lymphoproliferative disorders are a heterogeneous group of neoplasms with varying clinical, morphologic, immunophenotypic, and genetic characteristics. A subset of lymphomas have a proclivity for the gastrointestinal tract, although this region may also be involved by systemic lymphomas. In addition, a number of indolent lymphoproliferative disorders of the gastrointestinal tract have been defined over the past decade, and it is important to accurately differentiate these neoplasms to ensure that patients receive the proper management...