Which modality is better to diagnose high-grade transformation in retroperitoneal liposarcoma? Comparison of computed tomography, positron emission tomography, and magnetic resonance imaging.

BACKGROUND: Survival in patients with retroperitoneal liposarcoma (RPLS) depends on the surgical management of the dedifferentiated foci. The present study investigated the diagnostic yield of contrast-enhanced CT, 18F-fluorodeoxyglucose positron emission tomography (PET), and diffusion-weighted MRI in terms of dedifferentiated foci within the RPLS. METHODS: Patients treated with primary or recurrent RPLS who underwent the above imaging between January 2010 and December 2021 were retrospectively reviewed. The diagnostic accuracy of the three modalities for histologic subtype of dedifferentiated liposarcoma (DDLS) and French Federation of Cancer Center (FNCLCC) grade 2/3 were compared using receiver operating characteristic curves and areas under the curves (AUCs). RESULTS: The cohort involved 32 patients with 53 tumors; 30 of which exhibited DDLS and 31 of which did FNCLCC grades 2/3. The optimal thresholds for predicting DDLS were mean CT value of 31 Hounsfield Unit (HU) (AUC = 0.880, 95% CI 0.775-0.984; p < 0.001), maximum standardized uptake value (SUVmax) of 2.9 (AUC = 0.865 95% CI 0.792-0.980; p < 0.001), while MRI failed to differentiate DDLS. The cutoff values for distinguishing FNCLCC grades 1 and 2/3 were a mean CT value of 24 HU (AUC = 0.858, 95% CI 0.731-0.985; p < 0.001) and SUVmax of 2.9 (AUC = 0.885, 95% CI 0.792-0.978; p < 0.001). MRI had no sufficient power to separate these grades. CONCLUSIONS: Contrast-enhanced CT and PET were useful for predicting DDLS and FNCLCC grade 2/3, while MRI was inferior to these two modalities.

Histiocytic and dendritic cell neoplasms: Reappraisal of a Japanese series based on t(14;18) and neoplastic PD-L1 expression.

Histiocytic and dendritic cell (H/DC) neoplasms are heterogeneous, originating from myeloid- or stromal-derived cells. Multiple reports describe the cross-lineage transdifferentiation of neoplastic B cells into H/DC neoplasms. Most such cases are from Western countries, and rarely from Japan or East Asia. Here we report 17 cases of H/DC neoplasms in Japanese patients, with analysis of t(14;18) by fluorescence in situ hybridization, and of neoplastic programmed death-ligand 1 (PD-L1) expression by immunostaining (clones SP142, E1J2J, and 28-8). These 17 cases were diagnosed according to the 2017 World Health Organization (WHO) classification, and included two histiocytic sarcomas (HS), two interdigitating cell (IDC) sarcomas, one Langerhans cell sarcoma, two dendritic cell sarcomas, and 10 follicular dendritic cell (FDC) sarcomas. No case had any past history of follicular lymphoma (FL). Two cases of HS and one IDC sarcoma, all of which were myeloid-driven, were found to exhibit t(14;18). In the latter case, at 30 months after IDC sarcoma diagnosis, FL development was detected. Three (30%) FDC sarcoma cases exhibited neoplastic PD-L1 expression with all the three PD-L1 antibody clones. This is the first report of t(14;18) and neoplastic PD-L1 expression on H/DC neoplasms among Japanese patients, each of which appeared to be associated with HS and FDC sarcoma, respectively.

PD-L1 expression on tumor or stromal cells of nodal cytotoxic T-cell lymphoma: A clinicopathological study of 50 cases.

Inhibitors of programmed cell-death 1 (PD-1) and programmed cell-death ligand 1 (PD-L1) have revolutionized cancer therapy. Nodal cytotoxic T-cell lymphoma (CTL) is characterized by a poorer prognosis compared to nodal non-CTLs. Here we investigated PD-L1 expression in 50 nodal CTL patients, with and without EBV association (25 of each). We identified seven patients (14%) with neoplastic PD-L1 (nPD-L1) expression on tumor cells, including three males and four females, with a median age of 66 years. One of the seven cases was TCRαß type, three were TCRγδ type and three were TCR-silent type. Six of the seven cases exhibited a lethal clinical course despite multi-agent chemotherapy, of whom four patients died within one year of diagnosis. Morphological findings were uniform, with six cases showing centroblastoid appearance. Among nPD-L1+ cases, two of three examined had structural variations of PD-L1 disrupting 3'-UTR region. Notably, all of the TCRγδ-type nodal CTL cases showed nPD-L1 or miPD-L1 positivity (3 and 10 cases, respectively). TCRγδ-type cases comprised 42% of nPD-L1+ cases (P = 0.043 vs. PD-L1- ), and 35% of miPD-L1+ cases (P = 0.037 vs. PD-L1- ). The results indicate that PD-L1+ nodal CTL cases, especially of the TCRγδ type, are potential candidates for anti-PD-1/PD-L1 therapies.

Age-related EBV-associated B-cell lymphoproliferative disorders and other EBV + lymphoproliferative diseases: New insights into immune escape and immunodeficiency through staining with anti-PD-L1 antibody clone SP142.

Epstein-Barr virus (EBV) is prevalent among healthy individuals, and is implicated in numerous reactive and neoplastic processes in the immune system. The authors originally identified a series of senile or age-related EBV-associated B-cell lymphoproliferative disorders (LPD) bearing a resemblance to immunodeficiency-associated ones. These LPDs may be associated with immune senescence and are now incorporated into the revised 4th edition of 2017 WHO lymphoma classification as EBV-positive (EBV+) diffuse large B-cell lymphoma (DLBCL), not otherwise specified (NOS). These EBV+ B-cells often have a Hodgkin/Reed-Sternberg (HRS)-like appearance and are shared beyond the diagnostic categories of mature B-cell neoplasms, mature T-cell neoplasms, classic Hodgkin lymphoma, and immunodeficiency-associated LPD. In addition, peculiar new diseases, such as EBV+ mucocutaneous ulcer and EBV+ DLBCL affecting the young, were recognized. On the other hand, lymphoma classification is now evolving in accord with deeper understanding of the biology of programmed death ligand 1 (PD-L1). Assessing PD-L1 positivity by staining with the anti-PD-L1 monoclonal antibody SP142 provides new insight by discriminating between immune evasion and senescence or immunodeficiency. The aim of the present review is to briefly summarize the diagnostic use of immunostaining with SP142 in malignant lymphomas and/or LPDs that feature tumor and nonmalignant large B-cells harboring EBV.

Diagnostic utility of programmed cell death ligand 1 (clone SP142) in mediastinal composite lymphoma: A report of two cases.

Composite lymphoma is a well-known diagnostic entity exhibiting the synchronous occurrence of two or more distinct types of lymphomas in the same specimen. Here we report two patients, a 14-year-old female (Case 1) and a 45-year-old male (Case 2), with mediastinal composite lymphoma, comprising nodular sclerosis classic Hodgkin lymphoma (NSCHL) and primary mediastinal large B-cell lymphoma (PMBL). Both patients had a mediastinal mass, and manifested two different histologic components in the same biopsy, one characteristic of NSCHL and the other PMBL. The NSCHL areas included Hodgkin and Reed-Sternberg (HRS) cells with typical immunophenotypic features (CD30-positive and CD20-negative), whereas the sheets of large tumor cells characteristic of PMBL were strongly and uniformly CD20-positive. Interestingly, although both cases showed neoplastic PD-L1 (nPD-L1) positivity on the HRS cells of NSCHL, they differed regarding nPD-L1 expression on the PMBL tumor cells. In Case 1, the nPD-L1-negative PMBL component was anatomically situated outside the NSCHL lesion. On the other hand, in Case 2, the nPD-L1-positive PMBL component was characterized by transitional or continuous areas with the NSCHL component. These findings suggested that nPD-L1 expression may define two subtypes of PMBL that are more similar to or distinct from classic Hodgkin lymphoma.

Syncytial variant of classic Hodgkin lymphoma: Four cases diagnosed with the aid of CD274/programmed cell death ligand 1 immunohistochemistry.

Although several reports have highlighted neoplastic PD-L1 (nPD-L1) expression in classic Hodgkin lymphoma (CHL), some have addressed associations between its expression and detailed histopathologic features. Here we describe four cases of syncytial variant of CHL (SV-CHL), with and without Epstein-Barr virus (EBV) association, and highlight the diagnostic utility of PD-L1 (clone SP142) immunohistochemistry. The patients were a 61-year-old male, 45-year-old male, 85-year-old female, and 89-year-old female. All presented with cervical or axillary lymphadenopathy, which on biopsy had the established histopathologic features of SV-CHL with a biphasic pattern of cohesive sheets of large tumor cells and typically scattered distribution of Hodgkin and Reed-Stenberg (HRS) cells. These tumor cells showed identical immunophenotypic findings for CD15, CD30, Fascin, PAX5, OCT2, BOB1 and EBV harboring, regardless of location. The exception was absent or decreased expression of nPD-L1 from tumor cells in the confluent sheets, contrasting with HRS cell positivity in typical areas of CHL. These findings offer the first suggestion of possible downregulation of nPD-L1 expression in association with the histopathologic progression of CHL. The results may be relevant for recognizing 'confluent' sheets in the diagnostic workup for SV-CHL.

Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma arising in patient with a history of EBV-positive mucocutaneous ulcer and EBV-positive nodal polymorphous B-lymphoproliferative disorder.

Elderly patients with Epstein-Barr virus (EBV) infection are at increased risk for developing B-cell lymphoproliferative disorder (B-LPD) due to immunosenescence. Here, we describe a case of a 75-year-old man who developed an EBV-positive (EBV+) mucocutaneous ulcer (EBVMCU) in the gingiva with spontaneous regression. Eighteen months after regression, he had a cervical lymph node enlargement that was diagnosed as EBV+ nodal polymorphous B-LPD, Ann Arbor stage IA. Clinicians decided to observe his clinical course without any treatment. Fourteen months later, the patient developed EBV-positive diffuse large B-cell lymphoma (DLBCL), Ann Arbor stage IIA, and received six courses of age-adjusted dose chemotherapy and achieved a complete remission. No evidence of a clonal relationship was found among these three lesions by standard polymerase chain reaction (PCR) analysis for immunoglobulin heavy chain. However, they all had expression of PD-L1 in the EBV+ large B-cells and Hodgkin Reed-Sternberg-like cells. This is the first case report of a PD-L1-positive (PD-L1+) EBVMCU and the development of multiple EBV-driven B-LPDs in the setting of immunosenescence within a 32-month period.

Divergence and heterogeneity of neoplastic PD-L1 expression: Two autopsy case reports of intravascular large B-cell lymphoma.

Intravascular large B-cell lymphoma (IVLBCL) is a distinct disease, but the neoplastic PD-L1 expression on tumor cells may vary among cases. We evaluated 10 IVLBCL autopsy cases for neoplastic PD-L1 expression, and had positive results in two cases. In one case, neoplastic PD-L1 expression (SP142, 28-8, and E1J2J clones) was dependent on the organ and anatomical site (capillaries vs. vessels) of the tumor tissue. Neoplastic PD-L1 expression was found in tumor cells located in capillaries in the central nervous system, pituitary gland, kidneys, lung, and gastrointestinal tract; sinuses/sinusoids of the spleen, liver, bone marrow, and lymph nodes; and an extravascular location. However, this expression was not detected in tumor cells located in the adrenal gland, thyroid gland, pancreas, ovaries, uterus, pleura, and small or larger-sized vessels of the lung. The other case showed constant neoplastic PD-L1 expression on the tumor cells, and in addition to the affected organs, capillaries, and vessels with two anti-PD-L1 antibodies (28-8 and E1J2J, but not SP142). The divergence and heterogeneity of neoplastic PD-L1 expression were clearly demonstrated in our cases. To the best of our knowledge, this is the first description of divergent neoplastic PD-L1 expression among the affected organs and anatomical sites in IVLBCL.

Anaplastic variant of diffuse large B-cell lymphoma: Reappraisal as a nodal disease with sinusoidal involvement.

Anaplastic variant (av) of diffuse large B-cell lymphoma (DLBCL) is morphologically defined in the 2017 World Health Organization classification, but still an enigmatic disease in its clinicopathologic distinctiveness, posing the differential diagnostic problem from gray zone lymphoma (GZL) and classic Hodgkin lymphoma (cHL). Thirty-one cases previously diagnosed as avDLBCL were reassessed. Of these, 27 (87%) and 4 (13%) were node-based and extranodal diseases, respectively. They were further reclassified into nodal avDLBCL (n = 18), nodal CD30+ DLBCL with T-cell/histiocyte-rich large B-cell lymphoma-like features (CD30+ DLBCL-THRLBCL) (n = 6), GZL with features intermediate between DLBCL and cHL (n = 3) and CD30+ extranodal DLBCL, NOS (n = 4). The nodal avDLBCL cases had a sheet-like proliferation of large cells and/or Hodgkin/Reed-Sternberg (HRS)-like cells in 12 (67%) notably with a sinusoidal pattern in 16 (89%). They showed an expression of CD20 and/or CD79a in all and CD30 in 15 of 18. All of them were negative for PD-L1 on tumor cells, although HRS-like cells showed negativity or partial loss of other B-cell markers to varying degrees. The present study highlighted the distinctiveness of the nodal avDLBCL with sinusoidal pattern, but without neoplastic PD-L1 expression, which provide refined diagnostic criteria for a more precise pathologic and clinical characterization of this disease.

Immune evasion-related extranodal large B-cell lymphoma: A report of six patients with neoplastic PD-L1-positive extranodal diffuse large B-cell lymphoma.

We identified six patients with Epstein-Barr virus (EBV)-negative extranodal diffuse large B-cell lymphoma (DLBCL) and immunohistochemical expression of PD-L1 on their tumor cells by examining 283 DLBCL cases with the PD-L1 SP142 clone between 2015 and 2017. They consisted of two men and four women with a median age of 71 years, and were examined in an autopsy (n = 1) and biopsies from the adrenal gland (n = 2), skin (n = 1), pelvic cavity (n = 1), and kidney (n = 1). All showed a monomorphic population of large transformed B-cells leading to diagnoses of DLBCL with two intravascular large B-cell lymphoma (IVLBCL) and one de novo CD5+ type and were featured by an invariable immunephenotype: CD3-, CD20+, BCL-2+, and MUM1+. In addition, CD5 and CD10 were each detected in one case. All cases expressed PD-L1 on >10% to >90% of tumor cells, which was confirmed with two other PD-L1 antibodies (E1J2J and 28-8). Three untreated patients had a rapid, lethal clinical course within 7 months after diagnosis; while, the remaining three achieved complete remission after treatment and were alive at the last follow-up. We suggest immune evasion-related extranodal large B-cell lymphoma should be recognized beyond the currently identified entities of IVLBCL and de novo CD5+ DLBCL.

Reappraisal of nodal Epstein-Barr Virus-negative cytotoxic T-cell lymphoma: Identification of indolent CD5+ diseases.

Nodal cytotoxic molecule (CM)-positive peripheral T-cell lymphoma (CTL) has recently been recognized as a clinicopathologically distinct disease. To further characterize this disease, here we compared 58 patients with Epstein-Barr virus (EBV)-negative CTL to 48 patients with EBV-positive CTL. The two groups did not differ in histopathology, T-cell receptor (TCR) expression or rearrangement incidences, or survival curves. However, patients with EBV-negative CTL less frequently showed hepatic involvement (P = .007), B symptoms (P = .020), hemophagocytosis (P = .024), and detectable CD4 (P = .002) and CD5 (P = .009). Univariate and multivariate analyses identified three factors that independently predicted favorable survival, onset age <60 years (P = .002), CD5 expression (P = .002), and mixed morphology (P = .013), TCRαß was not an independent predictor (P = .30), but was strongly linked with long survivorship among patients younger than 60 years old. A prognostic model incorporating these factors worked well for prognostic delineation, independently of the International Prognostic Index (P = .007 vs P = .082) and Prognostic Index for PTCL (P = .020 vs P = .15). Moreover, this constellation of findings indicated two nodal indolent diseases: CD5+ TCRαß (n = 13), and CD5+ NK-cell type lacking TCR expression or clonal TCRγ rearrangement (n = 4). The survival curves for these two groups were significantly superior to others (n = 29, P < .001). These diseases appear to be unique in their indolent clinical behavior, and should be managed differently from other diseases.

Immunohistochemical assessment of the diagnostic utility of PD-L1: a preliminary analysis of anti-PD-L1 antibody (SP142) for lymphoproliferative diseases with tumour and non-malignant Hodgkin-Reed-Sternberg (HRS)-like cells.

AIMS: The programmed death 1 (PD1)/PD1 ligand (PD-L1) axis plays an important role in tumour cells escape from immune control. PD-L1 immunohistochemistry is a useful predictor of immunotherapy response, but is still not used widely in the diagnostic setting. Here we describe results using PD-L1 immunohistochemistry during routine diagnostics in lymphoma. METHODS AND RESULTS: Ninety-one lymphoproliferative disease cases sharing tumour and non-malignant Hodgkin-Reed-Sternberg (HRS)-like cells with and without Epstein-Barr virus (EBV) association were investigated by immunohistochemistry for PD-L1 (clone SP142). PD-L1 expression was present in more than 5% of tumour or non-malignant HRS-like cells in 100% of EBV+ classical (C) Hodgkin lymphoma (HL) (n = 10) and EBV-negative nodular sclerosis CHL (n = 8); 40% of EBV+ diffuse large B cell lymphoma, not otherwise specified (DLBCL-NOS) (n = 20); and 4% of nodal peripheral T cell lymphoma of follicular helper T cell type (PTCL-TFH) (n = 22). In contrast, nodular lymphocyte-predominant HL (n = 4), lymphocyte-rich CHL (n = 6), EBV+ hyperplasia (n = 8), plasmablastic lymphoma (n = 3) and anaplastic lymphoma kinase-negative anaplastic large cell lymphoma (n = 5) seldom exhibited PD-L1 in their large cells. Assessing PD-L1 positivity in tumour and non-malignant large cells was helpful in differentiating between CHL versus nodal PTCL-TFH (P < 0.0001) or EBV+ DLBCL-NOS (P = 0.0052) and between EBV+ DLBCL-NOS versus nodal PTCL-TFH (P = 0.0052), with PD-L1 expression indicating the first diagnosis in each of those sets. CONCLUSION: Immunohistochemical evaluation of PD-L1 expression in tumour and non-malignant HRS-like large cells may be useful for assessing either immune escape or immunodeficiency in their pathogenesis.

Comparison of Epstein-Barr virus-positive mucocutaneous ulcer associated with treated lymphoma or methotrexate in Japan.

AIMS: The aim of the present study was to compare treated lymphoma-associated Epstein-Barr virus (EBV)-positive mucocutaneous ulcer (EBVMCU) and methotrexate (MTX)-associated EBVMCU. METHODS AND RESULTS: Of a series of 15 Japanese patients (11 women, four men; median age 74 years, range 35-84 years), seven received MTX for the treatment of autoimmune disease and eight developed EBVMCU after treatment of malignant lymphoma [diffuse large B-cell lymphoma (n = 4) without EBV association, adult T-cell leukaemia/lymphoma (n = 2), angioimmunoblastic T-cell lymphoma (n = 1), and follicular lymphoma (n = 1)]. Ulcers were observed in the oral cavity (n = 11), gastrointestinal tract (n = 2), and skin (n = 2). All were histologically characterised by a mixture of EBV-positive large B-cell proliferation and Hodgkin/Reed-Sternberg-like cells on a polymorphous background. A total of 46% (6/13) had monoclonal immunoglobulin heavy chain gene rearrangement, but none had clonal T-cell receptor gene rearrangement. Spontaneous regression occurred in 13 of 15 cases (87%); the other two cases (13%) achieved complete remission after treatment. Of two patients in the treated lymphoma-associated subgroup, one developed multiple new ulcerative lesions on previously unaffected skin, and the other had a relapse of EBVMCU in the oral cavity. No significant clinicopathological differences were found between the subgroups. Notably, none of the patients died from EBVMCU. However, the treated lymphoma-associated subgroup had lower overall survival (P = 0.004) and a shorter follow-up period (P = 0.003) than the MTX-associated subgroup, owing to death from non-associated causes. CONCLUSIONS: Treated lymphoma-associated EBVMCU, which is an indolent and self-limited condition, must be recognised to avoid misdiagnosing it as a relapse of malignant lymphoma during treatment.

Anaplastic variant of diffuse large B-cell lymphoma with hallmark cell appearance: Two cases highlighting a broad diversity in the diagnostics.

The anaplastic variant of diffuse large B-cell lymphoma (A-DLBCL) is morphologically defined but remains an enigmatic disease in its clinicopathologic distinctiveness. Here, we report two cases involving Japanese women aged 59 years, both with A-DLBCL with the hallmark cell appearance and both indistinguishable from common and giant cell-rich patterns, respectively, of anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma. Case 1 was immunohistochemically positive for CD20, CD79a and OCT-2 but not for the other pan-B-cell markers, CD30 and ALK. Case 2 showed CD20 and CD30 positivity for 50% and 20% of tumor cells in addition to strong expression of p53 and MYC. Both were positive for fascin without Epstein-Barr virus association. Our cases provide additional support for the earlier reports that A-DLBCL exhibits clinicopathologic features distinct from ordinal diffuse large B-cell lymphoma (DLBCL), and documented its broader morphologic diversity than previously recognized. They also shed light on the unique feature of absent expression of pan-B-cell markers except for CD20 and CD79a, suggesting that A-DLBCL may biologically mimic a gray zone or intermediate lymphoma between DLBCL and classic Hodgkin lymphoma.

Case of primary central nervous system histiocytic sarcoma with prominent proliferation of histiocytic cells between the trabeculae of reactive glial cells.

Histiocytic sarcoma (HS) is an extremely rare malignant neoplasm that exhibits morphologic and immune-phenotype evidence of histiocytic differentiation. The disease most commonly involves the lymph nodes, gastrointestinal tract, skin, and soft tissue, as well as in the central nervous system (CNS) being relatively rare. Here we report a case of primary CNS HS with unusual histopathological characteristics. A 65-year-old woman presented with CNS HS in the left frontal lobe region, showing two distinct histological patterns. Approximately half of the lesion displayed histological characteristics typical of HS, including diffuse invasion of large round-to-ovoid pleomorphic cells, with mitotic figures (Ki-67 index: 30%) and coagulative necrotic foci. The other half exhibited prominent proliferation of histiocytic cells between the trabeculae of reactive glial cells, with rare mitotic figures (Ki-67 index: < 1%) and no necrotic foci. There were transitions between two morphologies. The HS tumor cells and the histiocytic cells between the trabeculae of reactive glial cells possessed nearly identical histomorphologic and immunophenotypic features, although the HS tumor cells showed a more pronounced degree of cytologic atypia and mitotic activity. To our knowledge, this is the first reported case of HS with prominent proliferation of the histiocytic cells between the trabeculae of reactive glial cells. Here we present the detailed histological, immunohistochemical, and molecular findings. Investigating cases of HS may provide insight into the pathogenesis of this disease.

Diagnostic approach for classic Hodgkin lymphoma in small samples with an emphasis on PD-L1 expression and EBV harboring in tumor cells: a brief review from morphology to biology.

Classic Hodgkin lymphoma (CHL) was first described in 1832 by Thomas Hodgkin, and is characterized by a small number of Hodgkin and Reed-Sternberg cells in a rich inflammatory background. However, even in this modern era, due to the histological and biological overlap with CHL and other B-cell malignancies, including mediastinal grey zone lymphoma and other lymphomas accompanied by "Hodgkinoid cells", their discrimination is challenging and sometimes impossible. The complexity and ambiguity of the boundaries of CHL and its related diseases make the definition of CHL unresolved. Our group has studied the significance of PD-L1 expression and infection of Epstein-Barr virus (EBV) in the diagnosis of CHL, emphasizing their pathological role, clinical significance, and high reproducibility even in daily clinical practice. In this review, we summarize the diagnostic strategy of CHL and its histological lookalikes based on neoplastic PD-L1 expression and infection of EBV, and attempt a reappraisal of the definition of CHL.

Laminectomy triggers symptomatic growth of spinal schwannoma in a patient with schwannomatosis.

Background: Schwannomatosis (SWN) is genetically similar to neurofibromatosis type 2 (NF2) and represents a NF2 gene mutation. Previous studies have shown that these mutations in both neurons and Schwann cells can lead to the development of schwannomas after nerve crush injuries. Here, we reviewed the potential pathoanatomical mechanisms for the development of a trauma-induced spinal schwannomas in a 55-year-old male with SWN. Case Description: A 49-year-old male had originally undergone a L3-L5 lumbar laminectomy for stenosis; the schwannomas seen on the preoperative magnetic resonance imaging (MRI) were not resected. Now at age 55, he newly presented with low back pain and numbness in the left L5 dermatome, and he was diagnosed with an L4 vertebral level cauda equina tumor on MRI. Following gross-total resection, the histopathological assessment revealed a Ki-67 labeling index 5-10% in hotspots (i.e., slightly higher than the normal range of schwannomas) and a 20% mosaic loss of SMARCB1. Based on these criteria, he was diagnosed as having SWN. Conclusion: In this patient with SWN, compression/physical trauma to nerves of the cauda equina during the L3-L5 laminectomy 6 years ago likely caused the progression of schwannoma.

Two cases of solitary fibrous tumor/hemangiopericytoma with different clinical features according to the World Health Organization classification: case report and review of the literature.

Solitary fibrous tumors (SFTs) and hemangiopericytomas (HPCs) have been classified as one entity by the World Health Organization in 2016 due to gene fusion between NAB2 and STAT6. In the Central Nervous System (CNS), a hypocellular, collagenized tumor with a classic SFT phenotype is considered grade I, whereas more densely cellular tumors mostly corresponding to the HPC phenotype are classified as grade II or III (anaplastic) depending in mitotic count (<5 vs. >5 mitoses per 10 high-power fields). Herein, we report two cases of targeted SFT/HPC in which pathological differences and WHO grading affect clinical features. A 75-year-old woman presented with headache and had an intradural extramedullary tumor at the C1 to C2 level. The tumor was well-circumscribed and attached only to the dura mater. It was totally removed and diagnosed SFT/HPC grade I. In contrast, a 68-year-old woman presented with numbness in the right upper limb and had an intradural extramedullary tumor at the medulla to C3 levels The tumor was irregularly marginated and strongly adherent to the spinal cord and involved the vertebral artery. It was sub totally removed and diagnosed SFT/HPC grade II. To the best of our knowledge, there are only 12 cases of SFT/HPC at the craniocervical junction, including the present two cases, of which four that were adherent to the spinal cord or involved the vertebral artery were grade II or III. Although the location of the tumor was almost the same, there were significant differences in the intraoperative findings according to the WHO grading.