Small Round Blue Cell Morphology Research Articles

Abstract 4545: Integrative immune-genomic comparison of canonical Ewing sarcoma with Ewing-like mimics identifies potential targets for personalized therapies

Abstract Introduction: Ewing sarcoma (ES) is one of the most common types of small round cell sarcoma (SRCS) from the skeletal origin, characterized by small round blue cell morphology and FET-ETS fusions. However, recent NGS-based technology has dramatically increased the characterization of other SRCS entities that share morphological, pathological, and clinical similarity with canonical ES. Currently, these sarcomas are often treated with similar regimens derived from ES. Whether any subsets of these sarcomas might benefit from personalized anti-cancer strategies remains largely unknown. Methods: To explore potential therapeutic vulnerabilities, 51 FFPE samples from 49 patients (median age 31 years, 65.3% male) diagnosed as ES or its mimics by conventional pathology review were sent to DNA (OncoScreen®Plus) and RNA sequencing (OncoRNA, Burning Rock Biotech) for genomic and immune signature profiling. Tumor samples were classified into 5 groups based on their similarity with classic ES: (a) Canonical ES (n=12), defined as ES with EWSR1-FLI1fusion and a primary bone origin; (b) Non-canonical ES, which were found with either non-EWSR1-FLI1 FET-ETS fusion, or ES in extra-skeletal sites (n=11); (c) Non-FET-ETS fusion SRCS (n=10), defined as SRCS with gene fusions other than FET-ETS family; (d) Fusion-negative SRCS (n=4); and (e) non-SRCS, where the diagnosis was primarily suspected as ES but finally re-diagnosed as another histology (n=12). Results: The NGS-based diagnosis rectified the pathological diagnosis in 9/51 samples, including ES misdiagnosed as other (n=3), other misdiagnosed as ES (n=4), Non-FET-ETS fusion SRCS misdiagnosed as ES (n=1) and ALK fusion sarcoma misdiagnosed as SRCS (n=1). In the remaining 42 samples, 23 diagnoses were confirmed by both NGS and FISH, while 11 SRCS were negative in both NGS and FISH assay, yielding a concordance of 81.0% (34/42). In the 8 samples with discordant diagnosis, a definitive diagnosis was achieved by FISH but not NGS in 1 of 8 (12.5%), and vice versa in 7 of 8 (87.5%). Interestingly, genomic profiling revealed that Non-FET-ETS fusion SRCS had high frequencies of TP53 mutations (40%) and copy number loss (including 30% in CD274 and JAK2; 20% in PTCH1, CDKN2A/B, and MTAP) and featured higher levels of homologous recombination deficiency (HRD) (p=0.024) and chromosome instability (p=0.022) than other groups. Remarkably, non-canonical ES demonstrated upregulated PDCD1 expression (p=0.034). The distribution of immune hot and cold subtypes was comparable among all groups (p=0.334). Conclusion: Our study shows that NGS could efficiently facilitate the definitive diagnosis of ES and its mimics. We also revealed a diverse immune-genomic landscape of these SRCS, indicative of potential therapeutic opportunities targeting HRD and immune check-point in specific subtypes of these sarcoma entities. Citation Format: Zhusheng Zhang, Qiyuan Bao, Junxiang Wen, Zhuochao Liu, Qi Liu, Yuhui Shen, Lin Shao, Bing Li, Song-An Chen, Weibin Zhang. Integrative immune-genomic comparison of canonical Ewing sarcoma with Ewing-like mimics identifies potential targets for personalized therapies. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4545.

A rare paediatric renal tumour, clear cell sarcoma of kidney

Clear cell sarcoma of kidney is a rare paediatric malignant renal neoplasm which affects children in the 2nd and 3rd year of life. It has a propensity to metastasize to bones, lungs and brain and has a tendency to recur after treatment. The renal biopsy showed classic pattern of clear cell sarcoma of kidney confirmed with immunohistochemical markers and the subsequent post neoadjuvant nephrectomy showed predominantly myxoid pattern possibly due to treatment effects. Since the tumour mimics other paediatric malignant neoplasms with small round blue cell morphology, immunohistochemical markers play a prime role in differentiating them for effective treatment with doxorubicin. Due to aggressive nature and poor prognostic features of clear cell sarcoma of the kidney, it is important to diagnose this tumour and exclude the common neoplasms occurring at this age group prior to neoadjuvant treatment. 1.Argani P, Perlman EJ, Breslow NE, et al. Clear cell sarcoma of the kidney: a review of 351 cases from the National Wilms Tumor Study Group Pathology Center. Am J Surg Pathol 2000; 24: 4–18.2.Ooms AHAG, Vujanić GM, D'Hooghe E, et al. Renal tumors of childhood-a histopathologic pattern-based diagnostic approach. Cancers 2020; 12: 729.3.Kao YC, Sung YS, Zhang L, et al. BCOR overexpression is a highly sensitive marker in round cell sarcomas with BCOR genetic abnormalities. Am J Surg Pathol 2016; 40: 1670–8.

Pathological features of primary extragonadal germ cell tumor of the prostate with small round blue cell morphology

Objective: To investigate the clinicopathological features and clinical management of primary extragonadal germ cell tumor of the prostate. Methods: Two cases of primary extragonadal germ cell tumor in the prostate were collected at Fudan University Shanghai Cancer Center, in January and September 2016, respectively. Their pathological features, clinical treatments and follow-up were retrospectively analyzed. Results: The two patients were 41 and 32 years old, respectively, and both presented with obstructive symptoms of the lower urinary tract. Histologically, both cases showed small round blue cells and an invasive growth pattern. The immunohistochemistry (IHC) stains of SALL4, OCT3/4, CD117 and PLAP were all positive, while those of PSA, AR and syn were negative. Moreover, case 1 demonstrated perinuclear dot-like staining for CKpan, which might be a diagnostic pitfall. There was no evidence of disease in other areas via physical examination or radiographic studies. Based on these IHC findings and the morphology, the two cases were diagnosed as primary seminoma of the prostate, which were consequently treated with six cycles of bleomycin, etoposide and cisplatin-based chemotherapy. A complete response was achieved in case 1. Case 2 was followed up and showed tumor recurrence, and progression with elevated tumor marker AFP. The subsequent radical removed specimens of case 2 were finally diagnosed as mixed germ cell tumor of the prostate. Conclusion: As a rare neoplastic entity, primary germ cell tumor of the prostate can show small blue round cell morphology. Pathologically, the morphology of small round blue cells combined with a perinuclear dot-like pattern of CKpan IHC staining may be a diagnostic pitfall. The clinical treatment strategy should be evaluated with consideration of the pathological diagnosis and comprehensive evaluation of the tumor markers.

Primary ewing sarcoma/primitive neuroectodermal tumor of the kidney

Abstract Background Primary renal Ewing/PNET (primitive neuroectodermal tumor) is a rare yet highly aggressive tumor affecting mainly the young population. The first case described of primary renal Ewing/PNET was in 1975 by Seemayer et al. Ever since then, this entity has been a dilemma for pathologists to diagnose. Both clinical presentation and radiological imaging are nonspecific; patients are generally presenting with nonspecific symptoms such as abdominal mass/pain or hematuria and with radiology that shows a heterogeneous renal mass. Also, under the microscope, the pathologist is faced with a sea of tumor cells having small round blue cell morphology. Case presentation A 16 years old male, presented to the emergency department of King Fahd University Hospital with gross painless hematuria and right flank pain for the last two months. Contrast-enhanced computerized tomography scan (CT-scan) showed a large heterogeneous right kidney mass with a large central cystic component. Also, a left subpleural lung nodule and para-aortic lymphadenopathy were identified. The patient underwent radical nephrectomy. Under the microscopic, a hypercellular lesion consisting of solid sheets of small blue round cells was identified. The immunohistochemical profile of the neoplastic cells showed positive reactivity for CD99 (diffuse membranous staining), S100, and Vimentin. Fluorescent in situ hybridization (FISH) analysis of EWSR1 break-apart showed evidence of a 22q12 rearrangement. So, the final diagnosis of primary kidney Ewing sarcoma was established based on clinical, pathological, and molecular results. He received five cycles of adjuvant chemotherapy. The patient has been in regular follow-up CT scans, which has been showing no new lesions, the last of which was done January 2020. Conclusion We report this case of renal Ewing/PNET to enrich the pool of reported cases in the literature of this rare entity. These tumors, in general, have unfavorable prognosis. Early accurate diagnosis and appropriate management, can have a significant impact on the patient prognosis. Fortunately, like in the presented case, the patient had complete remission, which is rare for this tumor. Thus, we emphasize that pathologists and clinicians should have a low threshold of suspicion for diagnosing this entity, especially in this age group.

Gene of the month: BCOR

BCL-6 transcriptional corepressor (BCOR) gene is located at Xp11.4 and encodes a protein which is involved in transcriptional repression in association with BCL-6 and epigenetic silencing through polycomb repressive complex...

Melanotic Neuroectodermal Tumor of Infancy.

Melanotic neuroectodermal tumor of infancy, albeit rare and generally regarded as benign, is an important tumor to recognize because of its rapid growth, potential for local recurrence, and small round blue cell morphology, which can lead to misdiagnosis of a malignant neoplasm. To review its clinical presentation and immunomorphologic findings, and discuss common entities in the differential diagnosis. The study involved PubMed searches, including multiple review articles, case studies, retrospective studies, selected book chapters, and University of Michigan cases. Melanotic neuroectodermal tumor of infancy most commonly occurs in the bones of the head and neck region during the first year of life, but it can also present in other locations, including the central nervous system, testes, ovaries, and subcutaneous soft tissues. Histologically, it is composed of a biphasic population of cells, consisting of epithelioid melanin-producing cells and primitive neurogenic cells in a fibrocollagenous stroma. These microscopic findings, especially in small biopsies, can lead to a broad differential diagnosis that includes malignant small round blue cell tumors and malignant melanoma. Melanotic neuroectodermal tumor of infancy commonly has an infiltrative growth pattern, and anatomic constraints often lead to incomplete resection and local recurrence, requiring multiple surgical operations. Because melanotic neuroectodermal tumor of infancy can mimic a more aggressive and aggressively treated malignancy, recognition of this rare tumor is very crucial for pathologists.

SOX10 Dot-Like Paranuclear Positivity in Merkel Cell Carcinoma

To the Editor: Merkel cell carcinoma (MCC) is a rare primary neuroendocrine tumor of the skin that is categorized into Merkel cell polyomavirus positive and negative lesions.1 MCC typically shows a malignant small round blue cell morphology, and although not by any means specific, the tumor has a characteristic dot-like paranuclear CK20 staining pattern. Electron microscopy studies have shown that these CK20 + paranuclear structures are composed of intermediate filaments.2 In this article, we present 2 cases of MCC with perinuclear dot-like expression of SOX10. The first patient was a 93-year-old man with advanced dementia who initially presented with painful rapidly growing soft-tissue lesions involving the left elbow, left index finger, and anatomical snuffbox of the left hand. A biopsy of the index finger at the time was consistent with MCC (Figs. 1A, B). The lesion had positive immunohistochemical staining for CD56, dot-like staining for neurofilament and CK20 (Fig. 1C), whereas CK7, TTF1, desmin, and S100-protein were negative. A positron emission tomography–computed tomography at the time of diagnosis was concerning for metastasis to the epitrochlear lymph node. Given his poor functional status, the clinical team opted for palliative radiation therapy without any additional treatment, and he died 6 months after the diagnosis was rendered. The second patient was a 62-year-old man with enlarging masses of 1 year duration at the right elbow, axilla, and dorsal arm. A biopsy of the right axilla was consistent with MCC (Figs. 2A, B). The lesion had immunohistochemistry positive for CD56 and synaptophysin and dot-like positivity for CK20 (Fig. 2C) and neurofilament, whereas CK7, CD99, TTF1, desmin, and P63 were negative. Imaging at the time of diagnosis was concerning for involvement of the right axillary and epitrochlear lymph nodes. After receiving radiation therapy and 12 cycles of Avelumab, he remains in remission approximately 6 months since the diagnosis was rendered. In both cases, SOX10 (Rabbit Polyclonal Primary Antibody, prediluted; Cell Marque, Rocklin, CA) was ordered as part of the initial diagnostic workup, and although not a diagnostic pitfall as only nuclear reaction is considered positive, the perinuclear dot-like staining pattern (Figs. 1D and 2D) was a peculiar observation that we have not encountered before and has not been previously reported in the literature.FIGURE 1.: Patient 1, (A) low power [hematoxylin and eosin (H&E) stain, ×40], (B) medium power (H&E stain, ×200), (C) medium power (CK20 stain, ×200), (D) medium power (SOX10 stain, ×200) demonstrating perinuclear dot-like positivity.FIGURE 2.: Patient 2, (A) low power (H&E stain, ×40), (B) medium power (H&E stain, ×200), (C) medium power (CK20 stain, ×200), (D) medium power (SOX10 stain, ×200) demonstrating perinuclear dot-like positivity.The SOX10 gene is a member of the SRY-related HMG-box family, which has roles in the development and specification of neural crest cells and the maintenance of both Schwann cells and melanocytes. SOX10 is typically negative in both MCC and in cells infected with the Merkel cell polyomavirus.3 Although perinuclear dot-like SOX10 staining has not been reported in MCC, it has been noted in colorectal carcinoma, in a series performed by the anti-SOX10 manufacturer Cell Marque.4 The exact mechanism for the perinuclear dot-like staining in our cases is unclear. Recently, 2 studies documented dot-like CD99 expression in 14/14 (100%)5 and 16/33 (48%)6 cases of MCC, respectively. It is unclear whether the paranuclear SOX10 staining pattern we observed is mechanistically related to either CD99 or CK20 paranuclear dot-like staining patterns because none of the stains have an obvious correlate. A CD99 stain obtained in one of the cases presented here showed a membranous staining pattern, dissimilar from the dot-like pattern described in the aforementioned studies. Proposed mechanisms in the case of CD99 have included staining of the Golgi apparatus, cross-reactivity with intermediate filaments, or antigen mix-reactivity.7 Indeed, similar mechanisms have been proposed for CD99 perinuclear dot-like staining pattern seen in other lesions including serous carcinoma of the endometrium with Ewing sarcoma/peripheral primitive neuroectodermal tumor differentiation,8 solid pseudopapillary tumor of the pancreas,9 colonic adenomas and adenocarcinomas,7 and anaplastic large-cell lymphoma.10 It is possible that perinuclear dot-like staining of SOX10 in MCC is an underreported phenomenon. Although not a diagnostic pitfall, it is mechanistically an interesting observation.

258 An Unusual Case of Retroperitoneal Poorly Differentiated Synovial Sarcoma in an Adolescent Boy

Poorly differentiated round cell variant synovial sarcoma is a rare neoplasm that typically arises in distal extremities of adults over 30 years. Importantly, it is associated with higher metastatic rate and worse outcome (five-year survival 20%) than conventional synovial sarcoma, necessitating its accurate identification. Our aim is to report an unusual case of retroperitoneal poorly differentiated synovial sarcoma that presented clinically as a slow growing mass in an adolescent boy. Retrospective review of a case of a 14-year-old obese boy with left-sided lower back mass that has been increasing in size for the past eight years. CT imaging showed the soft-tissue mass extending from the lumbar paraspinal region into the retroperitoneum. Interventional radiology-guided biopsies demonstrated a high-grade round blue tumor. Additional testing did not confirm a specific diagnosis, and the patient underwent a wide resection to reveal a 14.5 cm tan-white lobulated soft mass with hemorrhage and necrosis extending into the skeletal muscle and fibroadipose tissue. Histologically, the tumor had small round blue cell morphology with high- grade features including increased mitotic activity, necrosis, and lymphovascular invasion. Immunohistochemical stains showed diffuse positivity to vimentin and CD56, and focal positivity to Cam5.2, CD99, WT1, and S100. It was negative for EMA and Melan A, as well as a wide panel of smooth muscle, lymphoid, and neuroendocrine markers. Differential diagnosis included Ewing sarcoma, round cell liposarcoma, desmoplastic small round cell tumor, and MPNST. G-banded chromosomal karyotyping revealed the characteristic t(X;18) translocation helping to render the final diagnosis. Post-operatively, the patient underwent seven cycles of chemotherapy and is doing well at 1.5 years’ follow-up. This case highlights how cytogenetics can help in making the correct diagnosis particularly in unusual lesions that lack typical histological and immunohistochemical findings. Recognition of the poorly differentiated variant is critical because of poor prognosis.

Aberrant expression of FLI‐1 in melanoma

Friend leukemia integration site 1 (FLI-1) nuclear transcription factor has been proposed as a suitable tool in the differential diagnosis of small round cell sarcomas. It has also been described as a nuclear marker of endothelial differentiation. Expression of FLI-1 has been demonstrated in Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) and vascular neoplasms. In the present study, we describe 2 cases of metastatic melanoma with small round blue cell morphology that showed strong nuclear expression of FLI-1. Because of the small round blue cell morphology and negative immunohistochemical staining for pan-melanocytic cocktail (HMB45, anti MART1 and anti-tyrosinase) and SOX10 in both cases, FLI-1 immunostaining was requested as part of the tumors workup. Ultimately, both cases were established as being metastatic melanoma. Dermatopathologists should be aware that melanoma can be strongly positive for FLI-1 and not misinterpret these cases for ES/PNET or vascular lesions, especially when melanomas show unusual morphology.

Paediatric Peripheral Primitive Neuroectodermal Tumour - A Clinico-Pathological Study from Southern India.

Primitive Neuroectodermal Tumour (PNET)/Ewing Sarcomas (ES) are aggressive childhood malignancies with neuroectodermal differentiation. To study the clinical presentation, morphology, Immun-ohistochemistry (IHC), management and outcome of all the cases of paediatric pPNET/ES reported in our tertiary care centre over a period of six years. This was a retrospective study conducted at Sri Ramachandra Medical College and Research Institute, Chennai, India. All biopsy proven cases of peripheral PNET/ES, in patients less than 18 years of age for a period of six years were included in this study. The corresponding clinical details regarding initial presentation, treatment and follow up were retrieved from the case files and analysed. Survival rate was calculated and Kaplan-Meier survival curve was plotted. We describe eleven cases of paediatric peripheral PNET/ES. The mean age at presentation was 94.08 (±58.27) months with a male/female ratio of 1.2:1. About 27.3% cases, all male with a mean age of 140 months at presentation, had distant metastasis during initial diagnosis. Biopsy showed small round blue cell morphology on light microscopy. IHC revealed strong membranous staining for CD99 in all cases. All children were treated with neo-adjuvant chemotherapy and then surgery, followed by radiotherapy if indicated. The cases were followed up for a mean duration of 20.82 months (ranging from one to 66 months). Nine children are doing well on follow up (81.8% survival rate). Two cases with metastasis at initial presentation died. Patients with metastatic disease exhibited a mean duration of survival of 9.66 (±7.24) months and those with localized disease exhibited a mean duration of survival of 25 (±22.88) months. Metastasis at diagnosis is the single most important factor affecting prognosis. This was reflected in the present study where cases with metastasis exhibited a short mean duration of survival when compared to localized disease. It is likely that many cases of PNET/ES were not accurately identified in the past as IHC plays a vital role in the diagnosis of these small round blue cell tumours. IHC in adjunct with molecular studies has improved diagnostic accuracy. Multidisciplinary management and good supportive care when the lesion is localized has lead to improved survival.

Small round blue cell tumors of the sinonasal tract: a differential diagnosis approach

One of the most challenging diagnostic categories within tumors of the sinonasal tract is the small round blue cell tumors. Biopsies are usually small and limited, resulting in considerable diagnostic difficulty for practicing surgical pathologists. These tumors share several overlapping histologic and immunophenotypic findings while also showing considerable variation within and between cases. Specific tumor site of origin, imaging findings, and clinical findings must be combined with the histology and pertinent ancillary studies if the correct diagnosis is to be reached. Discrimination between neoplasms is critical as there are significant differences in therapy and overall outcome. It is important to have a well developed differential diagnosis for this category of tumors, where each of the diagnoses is considered, evaluated, and either confirmed or excluded from further consideration. In an undifferentiated tumor, showing a small round blue cell morphology, using the mnemonic ‘MR SLEEP' helps to highlight tumors to consider: melanoma, mesenchymal chondrosarcoma, rhabdomyosarcoma, sinonasal undifferentiated carcinoma, squamous cell carcinoma (including NUT carcinoma), small cell osteosarcoma, lymphoma, esthesioneuroblastoma (olfactory neuroblastoma), Ewing sarcoma/primitive neuroectodermal tumor, pituitary adenoma, and plasmacytoma. A panel of pertinent immunohistochemistry studies, histochemistries and/or molecular tests should aid in reaching a diagnosis, especially when taking the pattern and intensity of reactions into consideration.

Diagnostic Challenges in Pediatric Round Blue Cell Tumors of the Bone

Bone lesions, both neoplastic and non-neoplastic, are common in children. The accurate diagnosis is usually established following tissue sampling with histopathologic examination. However, those entities with predominant small round blue cell morphology can be diagnostically challenging. This review highlights distinctive morphologic and molecular features that can help pathologists when encountering these cases.

Ewing sarcoma family of tumours: unusual histological variants and immunophenotypic characteristics

Ewing sarcoma family of tumours are typified by small round blue cell morphology with variable but usually minimal neuroectodermal differentiation and non-random translocations involving the EWSR1 gene and a member of the ETS family of genes. Atypical morphological patterns may be seen in up to 20% of cases and include large cell, adamantinoma-like, spindle cell sarcoma-like (synovial sarcoma like), sclerosing, clear cell (hypernephroid)/anaplastic, and vascular like patterns. Immunophenotypically, CD99, vimentin, CAV1 and FLI1 are typically positive. Around half of the cases may express NSE and/or CD57. Low molecular weight cytokeratins (CK), S100, NB84, and CD117 are expressed less commonly (around 20%–40%). EMA, desmin, CD31, and synaptophysin expression are rare. CK7, CK20, D2-40, chromogranin, TDT, TTF, MYF4 appear to be consistently negative. Molecular confirmation is less sensitive. The correct diagnosis requires correlation between morphology and immunostaining, and may require molecular testing.