Atypical spindle cell/pleomorphic lipomatous tumor

A Rare Case of Breast fat-Forming Solitary Fibrous Tumor With Molecular Confirmation

Solitary fibrous tumor (SFT) is an uncommon fibroblastic neoplasm which may arise in a wide range of anatomic location and can occur across all ages. Fat-forming SFT is a rare morphological variant of SFT. Primary breast fat-forming SFT is exquisitely rare. Here, we report a case in a 51-year-old Chinese woman with a palpable painless mass in the left breast. A color Doppler ultrasound scan examination demonstrated a 3.4-cm oval, well-circumscribed, hypoechoic solid mass with several peripheral and internal color flow signals. Magnetic resonance imaging (MRI) showed a focal lobulated solid nodular lesion displaying geographical enhancement but no architectural distortion. Subsequently, she underwent a left breast lumpectomy. In histopathologic examination, there was a well-circumscribed, cellular spindle cell tumor consisting of short fascicles of bland, fusiform, ovoid to spindle cells disposed in a patternless architecture around branching vascular spaces within a fibrous stroma with wispy collagen. Cells revealed mild nuclear atypia. Mitotic figures were up to 4/10 high-power fields (HPFs) in the hot spot. Mature adipocytes intermixed with spindle cells were also observed. The tumor cells were diffusely positive for CD34 and STAT6. Some S100-expressing adipocytes co-expressed STAT6. Next-generation sequencing (NGS) revealed the presence of the NAB2exon6::STAT6exon2 fusion. The histological, immunohistochemical (IHC) and molecular examinations confirmed the diagnosis of fat-forming SFT. Post-excision, the patient showed no signs of tumor recurrence or metastasis in a 7-month follow-up. Here, we describe a rare case of a fat-forming SFT involving the breast and highlight the comprehensive pathological evaluation and necessary ancillary testing.

Case report: Atypical spindle cell/pleomorphic lipomatous tumor masquerading as a myxoid liposarcoma or intramuscular myxoma

Atypical spindle cell/pleomorphic lipomatous tumors (ASPLTs) were recently categorized as benign lipomatous tumors. However, accurate and complete preoperative diagnosis of ASPLTs may be difficult. Furthermore, diagnosis based on magnetic resonance imaging (MRI) findings is uncertain because of the varying ratios of the fat component within the tumor. Here, we report a case of ASPLT masquerading as a myxoid tumor. Although MRI findings were consistent with a myxoid liposarcoma, needle biopsy findings suggested a myxoma, and we performed marginal resection. Histopathological findings revealed infiltrating spindle cells with atypia. In addition, immunohistochemistry (IHC) showed positive staining for CD34 and heterogeneous retinoblastoma deficiency, and fluorescence in situ hybridization (FISH) showed no amplification of mouse double minute 2 homolog and no rearrangement of FUS or EWSR1. When MRI and histopathological findings suggest a myxoid tumor, IHC and FISH should be considered and performed for a precise and accurate diagnosis.

Large retroperitoneal atypical spindle cell lipomatous tumor, an extremely rare neoplasm: A case report

BACKGROUND

Atypical spindle cell lipomatous tumor (ASLT) is a rare soft tissue neoplasm with a low potential for malignancy. ASLT frequently occurs in the limb and limb girdles. However, large retroperitoneal ASLTs are extremely rare. There was no concrete case report of retroperitoneal ASLTs.

CASE SUMMARY

An 18-year-old woman presented with abdominal pain and a palpable mass. Abdominal computed tomography revealed a large fatty mass that was approximately 30 cm in size and filled the entire abdominal cavity. Surgical excision was indicated. The tumor did not invade the adjacent organs. The pelvic cavity was then too narrow to dissect smoothly. The mass was successfully excised without tumor rupture or adjacent organ injury. Microscopically, the neoplasm was a well-differentiated adipocytic neoplasm. Immunohistochemical staining showed that the spindle cells were positive for CD34 and desmin, in addition to multifocal positivity for S100 protein. These histological features were consistent with an ASLT. The patient’s postoperative course was uneventful. At the 12-mo follow-up, no evidence of recurrence or metastasis was observed.

CONCLUSION

To the best of our knowledge, our study is the first concrete report of a large retroperitoneal ASLT in the English literature. In the large retroperitoneal ASLT located in the pelvic cavity, which made it too narrow and tight to dissect, complete excision is difficult but very important because of recurrence risk. Although large retroperitoneal ASLTs are considered extremely rare, their detection is important for accurate evaluation and management. Owing to their significant rarity, retrospective multicenter case studies are required to determine the clinicopathologic characteristics.

Myxoid pleomorphic liposarcoma-a clinicopathologic, immunohistochemical, molecular genetic and epigenetic study of 12 cases, suggesting a possible relationship with conventional pleomorphic liposarcoma

Myxoid pleomorphic liposarcoma is a recently defined subtype of liposarcoma, which preferentially involves the mediastinum of young patients and shows mixed histological features of conventional myxoid liposarcoma and pleomorphic liposarcoma. While myxoid pleomorphic liposarcoma is known to lack the EWSR1/FUS-DDIT3 fusions characteristic of the former, additional genetic data are limited. To further understand this tumor type, we extensively examined a series of myxoid pleomorphic liposarcomas by fluorescence in situ hybridization (FISH), shallow whole genome sequencing (sWGS) and genome-wide DNA methylation profiling. The 12 tumors occurred in 6 females and 6 males, ranging from 17 to 58 years of age (mean 33 years, median 35 years), and were located in the mediastinum (n = 5), back, neck, cheek and leg, including thigh. Histologically, all cases consisted of relatively, bland, abundantly myxoid areas with a prominent capillary vasculature, admixed with much more cellular and less myxoid foci containing markedly pleomorphic spindled cells, numerous pleomorphic lipoblasts and elevated mitotic activity. Using sWGS, myxoid pleomorphic liposarcomas were found to have complex chromosomal alterations, including recurrent large chromosomal gains involving chromosomes 1, 6-8, 18-21 and losses involving chromosomes 13, 16 and 17. Losses in chromosome 13, in particular loss in 13q14 (including RB1, RCTB2, DLEU1, and ITM2B genes), were observed in 4 out of 8 cases analyzed. Additional FISH analyses confirmed the presence of a monoallelic RB1 deletion in 8/12 cases. Moreover, nuclear Rb expression was deficient in all studied cases. None showed DDIT3 gene rearrangement or MDM2 gene amplification. Using genome-wide DNA methylation profiling, myxoid pleomorphic liposarcomas and conventional pleomorphic liposarcomas formed a common methylation cluster, which segregated from conventional myxoid liposarcomas. While the morphologic, genetic and epigenetic characteristics of myxoid pleomorphic liposarcoma suggest a link with conventional pleomorphic liposarcoma, its distinctive clinical features support continued separate classification for the time being.

Well-Differentiated Liposarcoma of the Hypopharynx Exhibiting Myxoid Liposarcoma-like Morphology with MDM2 and DDIT3 Co-Amplification

Well-differentiated liposarcoma (WDL) is one of the most common soft tissue sarcomas in adults. It has a predilection for middle-aged males and arises in deep-seated locations such as retroperitoneum, mediastinum, and spermatic cord. Its occurrence in young individuals at the hypopharyngeal region is an exceedingly rare event. Myxoid liposarcoma (ML)-like changes can seldom occur in some cases of WDL, which makes the diagnosis of WDL more challenging. Amplification of DDIT3 gene in a subset of cases of WDL has shown to be associated with such unique morphology. Herein, we present a case of a 36-year-old gentleman who presented with difficulty in breathing and swallowing for 3 months duration. CT scan of the neck revealed a lesion along the posterior wall of the hypopharynx measuring 3.5 cm. Histopathologic examination revealed a tumor composed of lobules of oval to spindle cells in a prominent myxoid stroma with delicate chicken-wire vasculature. In the vicinity, there were lobules composed of variably sized adipocytes separated by thick fibrous septa that contains atypical hyperchromatic spindle cells. By immunohistochemistry, the tumor cells in both components were immunoreactive for CDK4, but negative for MDM2. Fluorescence in-situ hybridization (FISH) confirmed the presence of MDM2 gene amplification. There was no evidence of FUS-DDIT3 gene rearrangement, however, DDIT3 gene was also amplified. The diagnosis of well-differentiated liposarcoma with prominent myxoid stroma was rendered. This is the first documentation of WDL with ML-like morphology harboring co-amplification of MDM2 and DDIT3 in the hypopharynx.

The Rapidly Expanding Group of RB1-Deleted Soft Tissue Tumors: An Updated Review

The classification of soft tissue tumors has evolved considerably in the last decade, largely due to advances in understanding the pathogenetic basis of many of these, sometimes rare, tumors. Deletion of Retinoblastoma 1 (RB1), a well-known tumor suppressor gene, has been implicated in the tumorigenesis of a particular group of soft tissue neoplasms. This group of so-called “RB1-deleted soft tissue tumors” has been rapidly expanding in recent years, currently consisting of spindle cell/pleomorphic lipoma, atypical spindle cell/pleomorphic lipomatous tumor, pleomorphic liposarcoma, myofibroblastoma, cellular angiofibroma, and acral fibromyxoma. Most of these neoplasms, except pleomorphic liposarcoma, are considered benign entities and are mainly described in the older adult population. This article will review the currently known morphological, immunohistochemical, and molecular features of this heterogeneous group of mesenchymal tumors with an emphasis on differential diagnosis.