Alison L. Cheah

STAT6 rabbit monoclonal antibody is a robust diagnostic tool for the distinction of solitary fibrous tumour from its mimics.

Summary Recurrent NAB2-STAT6 gene fusions have recently been identified in solitary fibrous tumour by next generation sequencing. Our aim was to examine the sensitivity and specificity of STAT6 immunohistochemistry for solitary fibrous tumour versus other morphologically similar soft tissue tumours. STAT6 expression was evaluated in 54 solitary fibrous tumours of various sites and 99 soft tissue tumours in the histological differential diagnosis. We used a rabbit monoclonal STAT6 antibody (1:100), which has not been reported by others, on formalin fixed, paraffin embedded whole sections and tissue microarray slides. Only nuclear staining of STAT6 was considered positive. Distribution of staining was scored as: 0 (no staining), 1+ (1–25%), 2+ (26–50%), 3+ (>50%). Intensity was scored as weak, moderate or strong. Nuclear STAT6 staining was present in all SFT cases tested (54/54, sensitivity 100%), regardless of histology, anatomical site or CD34 status. The majority of cases showed 3+ and strong staining. All tested cases of cellular angiofibroma (0/9), myofibroblastoma (0/10), spindle cell lipoma (0/10), benign fibrous histiocytoma (0/13), dermatofibrosarcoma protruberans (0/9), low-grade fibromyxoid sarcoma (0/7), schwannoma (0/8), desmoid-type fibromatosis (0/8), monophasic synovial sarcoma (0/11), malignant peripheral nerve sheath tumour (0/7), and mesenchymal chondrosarcoma (0/7) were negative for STAT6 (specificity 100%). Our study further supports the utility of STAT6 immunohistochemistry as an adjunct in the diagnosis of solitary fibrous tumour.

Molecular diagnostics complementing morphology in superficial mesenchymal tumors

Molecular techniques are increasingly important in the practice of surgical pathology. In soft tissue tumors, there are a number of tumors with recurring cytogenetic abnormalities. Knowledge of these abnormalities has furthered our understanding of these tumors and has also allowed development of molecular techniques to aid in the diagnosis. This review will focus on mesenchymal tumors with specific cytogenetic abnormalities that may present as a superficial tumor of the dermis or subcutis.

Spindle cell/pleomorphic lipomas of the face: an under-recognized diagnosis

Rarely, spindle cell/pleomorphic lipomas arise on the face where they present diagnostic difficulties. The aim of our study was to describe the clinical, histological and immunohistochemical features of a series of spindle cell/pleomorphic lipomas of the face.

Mesenchymal tumours of the breast and their mimics: a review with approach to diagnosis

Mesenchymal tumours of the breast comprise a broad spectrum of entities that frequently pose diagnostic challenges to surgical pathologists. Metaplastic carcinoma and phyllodes tumour are site-specific mimics that account for the majority of tumours in the breast with a sarcomatoid appearance. Although uncommon, mammary tumours with fibroblastic, adipocytic or vascular differentiation may be encountered, spanning the spectrum from benign to malignant. Tumours with histiocytoid morphology are potential traps due to bland cytomorphology and resemblance to reactive processes. This comprehensive review provides a diagnostic approach to specific challenging mesenchymal tumours of the breast and their mimics, with a discussion on the salient morphological, immunohistochemical and molecular features that allow accurate diagnosis and will help the pathologist avoid potential pitfalls.

Primary clear cell sarcoma of the head and neck: a case series with review of the literature.

Clear cell sarcoma typically arises in deep soft tissues of the foot/ankle. Primary head and neck clear cell sarcoma is rare. We report three molecularly confirmed primary head and neck clear cell sarcoma and review the literature.

The role of molecular testing in the diagnosis of cutaneous soft tissue tumors.

A number of soft tissue tumors are characterized by recurring genetic abnormalities. The identification of these abnormalities has advanced our understanding of the biology of these tumors and has led to the development of molecular tests that are helpful diagnostically. This review will focus on the application of molecular diagnostic testing in select mesenchymal tumors of the dermis and subcutis.

Lipomatous tumors of the breast: A contemporary review

Breast tumors with lipomatous or liposarcomatous components are infrequently encountered, but can be a source of diagnostic difficulty if the context of the fatty differentiation is not recognized. Among the true adipocytic tumors, lipoma is the most common lipomatous tumor arising in the breast. Several mammary spindle cell tumors may show adipocytic differentiation, including fibroepithelial tumors and myofibroblastoma. Liposarcomatous components most often arise in malignant phyllodes tumors, as opposed to primary liposarcomas of the breast which are believed to be uncommon. This article will review the spectrum fat-containing tumors of the breast with an emphasis on differential diagnosis and insights from recent molecular studies.

Living on the Edge: Diagnosing Sarcomatoid Melanoma Using Histopathologic Cues at the Edge of a Dedifferentiated Tumor: A Report of 2 Cases and Review of the Literature

Abstract: Sarcomatoid melanoma is a rare type of melanoma lacking typical histologic features of melanoma and often lacks expression of S100 protein and melanocyte-specific markers. Given the rarity of this entity, its clinicopathologic findings are not well defined. We report 2 cases of sarcomatoid melanoma received in consultation: a 65-year-old woman with a right breast mass and a 62-year-old man with a left plantar heel mass. Both lesions were ulcerated, pedunculated, highly cellular proliferations of atypical spindle cells arranged as fascicles and/or sheets. The tumor cells of the breast mass expressed CD10 and vimentin diffusely but S100 protein only focally. The tumor cells of the heel mass lacked expression of melanocytic markers altogether, except for weak, very focal S100 protein expression. At the junctional edge of the breast mass and in the ulcer base of the heel mass, focal precursor melanoma was present and exhibited melanocytic differentiation. We report these cases to emphasize the importance of meticulous histologic inspection at the lesions edge and/or ulcer base to correctly identify the conventional precursor melanoma in these rare lesions to ensure appropriate diagnosis and subsequent clinical management as treatment options may be significantly different from those offered for sarcomas.