Extranodal histiocytic sarcoma: clinicopathologic analysis of 14 cases of a rare epithelioid malignancy

An advanced multisystem histiocytic sarcoma in a pregnant woman: A case report

Histiocytic sarcoma is an extremely rare disease that's hard to diagnose and treat, often leading to a poor prognosis. Here, we present a case report detailing a rare occurrence of HS in a 37-year-old pregnant woman who first presented with left shoulder pain, palpitations, and a productive cough at 20 weeks of gestation. Her diagnostic evaluations were performed, including different imaging modalities such as chest X-rays, CT scans, and MRI. Imaging revealed a large mediastinal mass with extensive involvement of the adrenal glands, lungs, and lymph nodes. The definitive diagnosis of HS is based on pathological and morphological features, and the immunohistochemistry report plays a key role. In our case, the diagnosis of HS was confirmed through pathological evaluation and immunohistochemistry, with a positive CD68 result obtained from a supraclavicular lymph node biopsy. A hospital committee comprising medical specialists like hematologists-oncologists, pathologists, pulmonologists, and obstetricians was brought together to assess the case collectively. The patient received chemotherapy, which alleviated her symptoms and maintained her condition. Based on the committee's recommendations, despite a healthy fetus and normal obstetric sonograms, the decision was made to terminate the pregnancy with the consent of the patient and her family. Despite initial improvement postchemotherapy, the patient's condition worsened, necessitating intubation. Tragically, two months after the initial admission, the patient passed away due to severe complications. In this case report, we provide a literature review and review of the patient's imaging reports. Since the patient is pregnant and HS is uncommon, it's important to highlight that this case is unique and worth sharing.

Histiocytic sarcoma affecting the oral cavity: a clinical, pathologic and molecular study

OBJECTIVE

To investigate the clinicopathological, immunohistochemical and molecular features of histiocytic sarcomas affecting the oral cavity.

METHODS

Pathology files of two institutions were searched for cases of histiocytic sarcoma, and new H&E-stained slides and immunohistochemistry reactions evaluated for diagnosis confirmation. Molecular screening for KRAS and PIK3CA mutations was performed through polymerase chain reaction (PCR) followed by Sanger sequencing. BRAFp.V600E mutation was assessed by pyrosequencing. Clinical data regarding sex, age, tumor location, systemic manifestations, clinical presentation, follow-up time, treatment applied and status at last follow-up were collected from patients' pathology and medical files.

RESULTS

Three cases were retrieved during the period investigated (2000-2023). Two females and one male were affected, with a wide age range, involving the tongue, palate and gingiva. Histopathologically, the neoplasms presented as highly pleomorphic atypical cells distributed diffusely with infiltration of normal structures. All cases demonstrated histiocytic differentiation expressing CD68 and CD163, and a high Ki67 expression. Genetic mutations were evaluated in two cases. One case harboured BRAF-V600E mutation, but not in KRAS and PIK3CA, while the second case did not show mutation in BRAF-V600E, KRAS and PI3KCA. One patient was lost, and two patients died after eight and four months of follow-up.

CONCLUSION

Histiocytic sarcomas involving the oral cavity are extremely rare, and may represent dissemination of a systemic condition. It has an aggressive biological behaviour with a poor overall prognosis.

NF1 mutation and TUBB3 amplification in gastric histiocytic sarcoma: a case report and literature review

Histiocytic sarcoma is a rare neoplasm of mature histiocytes with an aggressive clinical course and poor response to treatment. Primary gastric histiocytic sarcoma is rarer and just reported sporadically.Histiocytic sarcoma is a rare neoplasm of mature histiocytes with an aggressive clinical course and poor response to treatment. Primary gastric histiocytic sarcoma is rarer and just reported sporadically. A case of a 71-year-old female admitted with a one-year history of upper abdominal pain exacerbated after meals. After CT scans revealed a bulged mass at the lesser curvature of the gastric body, the patient underwent endoscopic submucosal dissection. Microscopically, non-cohesive neoplastic cells diffusely infiltrated lamina propria and submucosa, and diffusely expressed LCA, CD4, CD163, CD68 (KP1), Cyclin D1, Lysozyme, and Vimentin. PD-L1 (22CS) expression evaluated as CPS 60. The final pathological diagnosis was gastric histiocytic sarcoma. Subsequently, next-generation sequencing identified a nonsense mutation in exon 21 of NF1 gene [c.2446C > T (p.R816*)] and the TUBB3 gene amplification (copy number: 4.55). The patient refused further treatment and died of the tumor half a year later. This case broadens the spectrum of differential diagnosis of gastric cancer and emphasizes the value of immunohistochemical and molecular tests in the accurate diagnosis of histiocytic sarcoma. Furthermore, we performed literature review of 11 cases of gastric histiocytic sarcoma so as to strengthen the understanding of the clinicopathologic features, treatment, and prognosis.

Primary Histiocytic Sarcoma of the Breast: A Case Report and Review of the Literature

Histiocytic sarcoma (HS) is a rare cancerous tumor that originates from fully developed histiocytes. It is most often identified by the presence of certain proteins such as the cluster of differentiation (CD) 68, CD163, or lysozyme. HS has been recorded in different sites outside of the lymph nodes such as the gastrointestinal tract, nasal cavities, skin, and bone marrow. Because HS shares similar clinical features with other forms of malignant diseases, diagnosing it becomes incredibly challenging. We report a case of a 40-year-old female who presented with a breast mass for one year. A preliminary diagnosis of a phyllodes tumor was made. However, the morphology along with the immunophenotype picture was diagnostic for HS. Microscopic features showed a well-defined neoplastic growth arranged in sheets and fascicles. Diffuse immunoreactivity was seen for CD45, CD4, CD68, CD163, and vimentin. We present the important histopathological and immunohistochemical characteristics of the tumor in this case.

Primary pulmonary histiocytic sarcoma with high PD-L1 expression benefited from immunotherapy: A case report and bioinformatic analysis

Histiocytic sarcoma is an aggressive haematopoietic malignancy accounting for less than 1% of haematolymphoid neoplasms with a diagnosis based on morphology and immunophenotype of tissue biopsies with a very poor prognosis. Here, we report a 45-year-old man who was diagnosed with primary pulmonary histiocytic sarcoma with systemic metastases, with partial remission (PR) treated with cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) chemotherapy, but it relapsed soon after therapy above. Tests demonstrated that TMB was 21 Muts/Mb PD-L1 expression was 90% positive, and the disease has been well-controlled over 3 years using immune checkpoint inhibitors (nivolumab and pembrolizumab). Bioinformatic pan-cancer analysis verified that there was the highest genetic alteration frequency of PD-L1 in which amplification accounted for the majority of sarcoma tumour samples. Following that, we found that the genetic alteration of PD-L1 was associated with poor prognosis in sarcoma patients in terms of overall survival (OS) (p = 1.51 × 10-4 ), progress-free survival (PFS) (p = 4.90 × 10-2 ) and disease-specific survival (DSS) (p = 4.90 × 10-2 ). To our knowledge, this may be the first reported case with high PD-L1 expression in primary pulmonary histiocytic sarcoma who may benefit from immunotherapy such as nivolumab and pembrolizumab significantly and safely.

Histiocytic sarcoma mimicking localized tenosynovial giant cell tumor in the pediatric foot: A rare case report with MRI Findings

We present a rare case of histiocytic sarcoma (HS) occurring in the foot of a 12-year-old male, initially misdiagnosed as localized tenosynovial giant cell tumor (TSGCT). HS is an exceptionally uncommon hematologic malignant neoplasm, with its occurrence in children and extranodal sites being even rarer. To our knowledge, this is the first reported case of extranodal HS in the foot, emphasizing comprehensive MRI findings. Initially, the patient was diagnosed with TSGCT based on histological results following surgical resection. However, after recurrence and subsequent surgical resection, histological and immunochemical analyses led to a revised diagnosis of HS. This report focuses on the MRI findings of HS, highlighting the distinctions from localized TSGCT. While both conditions share histopathological similarities, immunohistochemical tests are crucial for accurate diagnosis. The report underscores the importance of differentiating HS for appropriate treatment.

Metastatic Histiocytic Sarcoma with Secondary Involvement of the Skin: A Case Report

Histiocytic sarcoma (HS) is a rare malignant neoplasm of presumed hematopoietic origin, showing morphologic and immunophenotypic evidence of histiocytic differentiation. A 61-year-old woman presented with an abdominal mass. She had a history of HS in both adrenal glands. The tumour cells of the left adrenal gland were very large epithelioid cells with abundant eosinophilic cytoplasm and large, round-to-oval nuclei. Similarly, the cutaneous lesion of the skin was composed of polygonal cells with well-defined cell borders and high nuclear/cytoplasm (N/C) ratios. Immunohistochemically, both tumours were positive for histiocyte-associated antigens but negative for epithelial, melanocyte, lymphoid, dendritic, and Langerhansl nuclei. Similarly, the cutaneous lesion of the skin was composenose correctly. It is important to recognise the morphological features and immunohistochemical characteristics of metastatic cells in order to achieve accurate diagnoses.

Enhanced Computed Tomography and 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in the Uncommon Histiocytic Sarcoma of Small Intestine Arising after Gastric Large B-Cell Lymphoma

Histiocytic sarcoma (HS) is an extremely rare and aggressive malignant neoplasm of hematopoietic origin that shows morphologic and immunophenotypic evidence of histiocytic differentiation. In approximately 25% of the cases, presumed transdifferentiation of a preexisting hematolymphoid disorder can be demonstrated. Various extranodal sites, particularly the gastrointestinal tract, soft tissue, skin, and spleen, can be involved. Enhanced CT and FDG PET/CT findings of extranodal histiocytic sarcoma have been barely reported. We present a case with extranodal HS originating in the small intestine after gastric large B-cell lymphoma, mistaken for prostate cancer metastasis in a 76-year-old man.

Histiocytic sarcoma in renal transplant patients: a literature review

BACKGROUND

Histiocytic sarcoma (HS) is defined as neoplasm resembling morphological and immunophenotypic characteristics of mature histiocytes. It is a rare form of lymphoid neoplasms. Despite advances in treatment and diagnosis of histiocytic sarcoma, majority of cases had poor prognosis due to progressive nature of the disease. In the following article, all reported cases of histiocytic sarcoma in renal transplant patients are reviewed.

METHODS

In our literature review, all relevant reports were collected electronically by entering the necessary keywords. A Boolean approach using Medical Subject Heading (MeSH) keywords was implemented. After establishing the inclusion/exclusion criteria, article titles and abstracts were evaluated by Systematic Reviews and Meta-Analyses (PRISMA) standards for 2020. All cases of histiocytic sarcoma in renal transplant patients were included.

RESULT

Based on our inclusion and exclusion criteria 4 case reports were yielded in this review. Two were males and 2 were females with the mean age of 42.25 years. Fever was the most common symptom. Although tumor originated from the native kidney on one patient, the site of the primary tumor was thorax, oropharynx, and transplanted kidney in the rest. Metastasis was detected in all cases. Prednisone was used for all cases. EBV was positive in 2 cases and negative in one of them. Histology was diagnostic and similar in all cases. Immunohistochemistry was done for 3 cases. Although chemotherapy was done for 3 patients, all 4 cases ended in mortality.

CONCLUSION

Despite the fact that neoplasms are post renal transplant complications, histiocytic sarcoma is a scarce and fatal entity in such patients. Histological and immunohistochemistry tests are the corner stone in diagnosis of histiocytic sarcoma.

The many faces of mouse histiocytic sarcoma in C57BL/6J mice

Histiocytic sarcoma is a tumor of the hematopoietic system considered to be derived from macrophages. Although rare in humans, it occurs frequently in mice. Histiocytic sarcoma can be a difficult tumor to diagnose due to its diverse cellular morphologies, growth patterns, and organ distributions. The varying morphology of histiocytic sarcomas makes it easy to confuse them with other types of neoplasia, including hepatic hemangiosarcoma, uterine schwannoma, leiomyosarcoma, uterine stromal cell tumor, intramedullary osteosarcoma, and myeloid leukemia. As such, immunohistochemistry (IHC) is often needed to differentiate histiocytic sarcomas from other common tumors in mice that they can morphologically mimic. The goal of this article is to present a broader perspective of the diverse cellular morphologies, growth patterns, organ distributions, and IHC labeling of histiocytic sarcomas encountered by the authors. This article describes these features in a set of 62 mouse histiocytic sarcomas, including the IHC characterization of the tumors using a panel of markers for the macrophage antigens F4/80, IBA1, MAC2, CD163, CD68, and lysozyme, and describes differentiating features of histiocytic sarcomas from other morphologically similar tumors. The genetic changes underlying the pathogenesis of histiocytic sarcoma in humans are beginning to be elucidated, but this is difficult due to its rarity. The higher prevalence of this tumor in mice provides opportunities to investigate mechanisms of its development and to test potential treatments.

TYMS promotes genomic instability and tumor progression in Ink4a/Arf null background

We previously showed that elevated TYMS exhibits oncogenic properties and promotes tumorigenesis after a long latency, suggesting cooperation with sequential somatic mutations. Here we report the cooperation of ectopic expression of human TYMS with loss of Ink4a/Arf, one of the most commonly mutated somatic events in human cancer. Using an hTS/Ink4a/Arf -/- genetically engineered mouse model we showed that deregulated TYMS expression in Ink4a/Arf null background accelerates tumorigenesis and metastasis. In addition, tumors from TYMS-expressing mice were associated with a phenotype of genomic instability including enhanced double strand DNA damage, aneuploidy and loss of G1/S checkpoint. Downregulation of TYMS in vitro decreased cell proliferation and sensitized tumor cells to antimetabolite chemotherapy. In addition, depletion of TYMS in vivo by TYMS shRNA reduced tumor incidence, delayed tumor progression and prolonged survival in hTS/Ink4a/Arf -/- mice. Our data shows that activation of TYMS in Ink4a/Arf null background enhances uncontrolled cell proliferation and tumor growth, supporting the development of new agents and strategies targeting TYMS to delay tumorigenesis and prolong survival.

Whole exome and transcriptome analysis revealed the activation of ERK and Akt signaling pathway in canine histiocytic sarcoma

Histiocytic sarcoma (HS) is an incurable aggressive tumor, and no consensus has been made on the treatment due to its rare occurrence. Since dogs spontaneously develop the disease and several cell lines are available, they have been advocated as translational animal models. In the present study, therefore, we explored gene mutations and aberrant molecular pathways in canine HS by next generation sequencing to identify molecular targets for treatment. Whole exome sequencing and RNA-sequencing revealed gene mutations related to receptor tyrosine kinase pathways and activation of ERK1/2, PI3K-AKT, and STAT3 pathways. Analysis by quantitative PCR and immunohistochemistry revealed that fibroblast growth factor receptor 1 (FGFR1) is over-expressed. Moreover, activation of ERK and Akt signaling were confirmed in all HS cell lines, and FGFR1 inhibitors showed dose-dependent growth inhibitory effects in two of the twelve canine HS cell lines. The findings obtained in the present study indicated that ERK and Akt signaling were activated in canine HS and drugs targeting FGFR1 might be effective in part of the cases. The present study provides translational evidence that leads to establishment of novel therapeutic strategies targeting ERK and Akt signaling in HS patients.

A long-term survival case of histiocytic sarcoma by surgery alone in a Japanese elderly breast tumor patient

INTRODUCTION

Histiocytic sarcoma (HS) is a rare hematologic malignancy. HS of the breast is extremely rare, and we present a case of an elderly patient with breast HS.

CASE PRESENTATION

An 81-year-old woman with unremarkable past medical and family histories presented to our hospital with a palpable mass in her right upper breast. She had noticed a mass in her right breast 3 months before her first visit. Physical examination revealed a mass measuring approximately 30 mm in the right upper quadrant of the breast; there were no cervical or axillary lymphadenopathies. Mammography revealed a high-concentration mass with unclear margins in the upper and outer breast. Ultrasound and magnetic resonance imaging (MRI) revealed a 31 × 23-mm nodule with a relatively clear margin and necrotic sign on the T2-intensified image. A mastectomy was performed upon the patient's request, and the surgical specimen revealed a 35-mm hemorrhagic mass. The lesion was estrogen receptor-, progesterone receptor-, and HER2/neu-negative. The Ki-67 labeling index was approximately 30%. The immunohistochemical panel showed immune reactivity for the histiocytic markers CD68, CD163, and CD206 and was immune-negative for B lineage, T lineage, Langerhans cells, and keratins. The diagnosis of HS was based on the morphological and immunophenotypic characteristics of the mass. The patient received no systemic therapy and survived for 50 months without recurrence.

CONCLUSIONS

Here, we report the case of an elderly patient with rare breast HS. Although the prognosis of HS seems poor, the breast HS was not as poor as expected, since it might have been discovered in the local region before it metastasized.

Combined use of pathological and genomic alteration analyses for the diagnosis of gray zone lymphoma

Histiocytic sarcoma (HS) is a rare malignancy showing morphologic and immunophenotypic features of histiocytes. HS has morphologic overlap with many other diseases, including various kinds of lymphomas. Gray zone lymphoma (GZL) is a rare B-cell lymphoma subtype characterized by overlapping features between diffuse large B-cell lymphoma and classic Hodgkin lymphoma. The histologic overlap with other diverse diseases of HS and the pathological diversity of GZL make it difficult to render a diagnosis. A 44-year-old woman who was initially diagnosed with HS was diagnosed with GZL after reexamination, including a genetic alteration test. After 6 cycles of brentuximab vedotin, doxorubicin, vinblastine, and dacarbazine, she achieved a complete response. Genomic alteration assessment may be useful for the accurate diagnosis of malignant lymphomas, which are difficult to diagnose, such as GZL.

Histiocytic Sarcoma Secondary to Gastrointestinal Stromal Tumors: A Literature Review

Histiocytic sarcoma (HS) is a rare tumor that may result from the transdifferentiation of preexisting hematolymphoid neoplasms in a subset of patients. There are instances of correlation or concurrence between HS and a number of cancers, particularly B-cell-associated hematopoietic tumors. Only three cases of HS occurring subsequent to or concurrently with gastrointestinal stromal tumors (GIST) have been recorded. Our main objective was to give an overview of demographics, clinical signs and symptoms, histopathological findings, and immunohistochemical and molecular analysis when HS develops secondary to or concurrently with GIST. A search of PubMed, Google Scholar, and ScienceDirect was undertaken using Medical Subject Headings (MeSH) keywords. According to the findings of our review, there were two males (66.6%) and one female (33.3%). The average age of patients at presentation was 59.6 years. On the immunohistochemistry, three patients were positive for cluster of differentiation (CD) 68 (100%), two patients were positive for CD 163 (67%), one patient was positive for leukocyte common antigen (LCA) (33%), and only one patient was positive for CD 4, CD 10, CD 31, CD 45, human leukocyte antigen (HLA)-DR, lysozyme, and vimentin (33%). On molecular investigation, the gastric mass of only one patient (33.33%) contained a KIT mutation on exon 11. Emperipolesis was observed in one patient (33.33%) on histological examination. Our study provides an important overview of the available literature and gives insight into important diagnostic markers of HS when it occurs secondary to or concurrently with GIST.

Multiple disciplinary team management of rare primary splenic malignancy: Two case reports

BACKGROUND

Malignant splenic tumors are rare but fatal, presenting a challenge in diagnosis and management involving hematology, oncology, and general surgery. By contrast, diagnosing and treating other common malignant tumors (such as lung and gastrointestinal cancer) offers multiple strategies for chemotherapy, radiotherapy, targeted therapy, and immunotherapy with the prospect of a cure. With various specialists involved in clinical multiple disciplinary team (MDT) discussion, personal bias can be minimized. It can also ignite important discussion which can benefit not only one patient but many patients.

CASE SUMMARY

Here, we report on the MDT diagnosis and management of the malignant splenic tumors littoral cell angiosarcoma and histiocytic sarcoma. Although only two cases of rare primary splenic malignancy are presented, MDT is a novel means of rare disease treatment.

CONCLUSION

To benefit patients, imaging analysis, safe operation, precise pathology examination, and individualized therapeutic treatment strategies are required. The involvement of various specialists in a clinical MDT discussion minimizes personal bias and can create important ideas to benefit all patients.

Histiocytic Sarcoma Involving Cervical Vertebra: A Case Report and Review of the Literature

Histiocytic sarcoma (HS) is a rare neoplasm composed of cells with immunohistochemical characteristics of mature histiocytes. It can be disseminated or localized and usually involves the skin, spleen, and gastrointestinal tract. Primary involvement of the vertebral column is extremely rare. We report a 29-year-old female who presented with neck pain and had a destructive 35*43*48 mm lesion in C2 with a paravertebral extension. The initial biopsy did not lead to the correct diagnosis. She later developed dysphagia, and the anterior approach was used for tumor decompression. The diagnosis of cervical histiocytic sarcoma was made, and she underwent radiotherapy. The follow-up MRI showed a marked response to radiotherapy. Here, we report the first case of cervical HS, review all cases of vertebral HS, compare patients’ characteristics and clinical courses, and discuss diagnostic nuances and treatment options.

Diagnostic utility of flow cytometry in identifying histiocytic sarcoma-A case report

Histiocytic sarcoma (HS) is a malignant neoplasm of hematopoietic origin. It is an exceedingly rare and aggressive malignancy commonly seen in adults. Diagnosis is difficult owing to lack of specific clinical manifestations with the absence of precursor lesions or causative agents. Hence, it primarily relies on histopathological morphology combined with immunohistochemistry, which is time-consuming, hence resulting in delayed treatment. However, diagnostic utility of flow cytometry is not well established in this. We report a case of a 45-year-old man who presented with right axillary lymphadenopathy for 1 month. FNAC was performed on the axillary lymph node, which showed large, atypical lymphoid/histiocyte-like cells. On flow cytometry, these cells were CD64+, CD11c+, and CD45+ suggesting histiocytic sarcoma. Similar morphology was seen on incisional biopsy. On immunohistochemistry, the cells were negative for B and T cell markers, PAX5, EMA, CK, ALK, and CD1a and expressed CD68, S100, and CD11c. A diagnosis of histiocytic sarcoma was made. Hence, flow cytometry can be a highly effective and powerful tool for the early detection of HS and can help in prompt treatment, given its aggressive clinical course and low survival interval.

A case of primary histiocytic sarcoma arising from a neck lymph node

Histiocytic sarcoma (HS) is an aggressive and rare hematological malignancy. Its treatment has not been established, and most patients die within 2 years of diagnosis. Resection can provide a favorable prognosis for solitary lesions. We present the case of an 80-year-old Japanese man with HS. He presented a history of a slow-growing painless mass in the lower part of his right jaw. Ultrasonography showed a swollen lymph node in the vicinity of the right submandibular gland. Contrast-enhanced computed tomography revealed a heterogeneous, low-contrast mass on the right of the neck. Magnetic resonance imaging revealed a heterogeneously enhanced mass in gadolinium-enhanced T1-weighted images. The fine needle biopsy showed spindle-shaped cells and HS was suspected. Fluorodeoxyglucose positron emission tomography revealed uptake by the tumor alone. The patient underwent right upper neck dissection and resection of the submandibular salivary glands. No postoperative adjuvant treatment was administered, but 2-year survival was achieved. Histopathological examination showed proliferation of large, pleomorphic atypical cells without differentiation into lymphocytes, which proved their differentiation into histiocytes. A bone marrow biopsy showed no evidence of monocytic leukemia. Thus, a diagnosis of HS was made. With local treatment alone, our patient achieved long-term survival, maintaining his quality of life.

Primary splenic histiocytic sarcoma successfully treated with splenectomy: a case report and literature review

A 61-year-old woman was referred to our hospital with refractory thrombocytopenia and splenomegaly. She was diagnosed with immune thrombocytopenia 3 years prior to admission and received steroid therapy. However, her platelet count started decreasing six months prior to admission. A diagnostic and therapeutic splenectomy was performed, which led to the diagnosis of histiocytic sarcoma. The patient's platelet count recovered promptly after splenectomy, and she was in complete remission for over a year.

Increased tumor-infiltrating lymphocyte density is associated with favorable outcomes in a comparative study of canine histiocytic sarcoma

Histiocytic sarcoma (HS) is a rare and aggressive tumor in humans with no universally agreed standard of care therapy. Spontaneous canine HS exhibits increased prevalence in specific breeds, shares key genetic and biologic similarities with the human disease, and occurs in an immunocompetent setting. Previous data allude to the immunogenicity of this disease in both species, highlighting the potential for their successful treatment with immunotherapy. Quantification of CD3 tumor-infiltrating lymphocytes (TIL) in five cases of human HS revealed variable intra-tumoral T cell infiltration. Due to the paucity of human cases and lack of current model systems in which to appraise associations between anti-tumor immunity and treatment-outcome in HS, we analyzed clinical data and quantified TIL in 18 dogs that were previously diagnosed with localized HS and treated with curative-intent tumor resection with or without adjuvant chemotherapy. As in humans, assessment of TIL in biopsy tissues taken at diagnosis reveal a spectrum of immunologically "cold" to "hot" tumors. Importantly, we show that increased CD3 and granzyme B TIL are positively associated with favorable outcomes in dogs following surgical resection. NanoString transcriptional analyses revealed increased T cell and antigen presentation transcripts associated with prolonged survival in canine pulmonary HS and a decreased tumor immunogenicity profile associated with shorter survivals in splenic HS. Based on these findings, we propose that spontaneous canine HS is an accessible and powerful novel model to study tumor immunology and will provide a unique platform to preclinically appraise the efficacy and tolerability of anti-cancer immunotherapies for HS.

Nonlymphoid Hematopoietic Diseases Presenting in Bone, Soft Tissue, and Other Extranodal Sites

Context.—

Although rare in everyday practice, the initial presentation of hematopoietic neoplasms other than lymphoma in the musculoskeletal system and other extranodal sites can generate challenging diagnostic problems for surgical pathologists.

Objective.—

To review the morphologic and immunophenotypic features of various nonlymphoid hematopoietic diseases presenting at extranodal sites, with emphasis on the inherent diagnostic pitfalls and differential diagnoses of these entities to aid surgical pathologists in their accurate recognition.

Data Sources.—

Cases reviewed herein represent both in-house and consult cases seen at our institution between 2010 and 2021.

Conclusions.—

Entities that present in this way include myeloid neoplasms and histiocytic/dendritic cell neoplasms. These tumors commonly cause nonspecific symptoms, and their histologic appearance can overlap with a variety of benign neoplasms and reactive processes. This can lead to delay in diagnosis and intervention with potentially lifesaving therapy; thus, accurate and expedient recognition is of paramount importance.

Sudden Unexpected Death Caused by Cardiac Metastasization from Histiocytic Sarcoma

BACKGROUND

Haematological malignancies, such as lymphoma and leukaemia, can have a variety of clinical manifestations. The most frequent cause of death from haematological malignancies is multiple organ failure due to neoplastic organ infiltration and/or septic shock. Histiocytic sarcoma (HS) is a rare malignant nodal or extranodal tumour with histiocytic immunophenotype that originates from a lymphohematopoietic precursor. The patients with HS usually have a poor prognosis due to its aggressive clinical behaviour. Rare cases of undiagnosed sudden HS death have been described in the literature.

METHODS

A forensic autopsy of a 46-year-old white male who died at home suddenly and unexpectedly without warning conditions or known diseases. Gross analysis, histology and toxicology were also performed.

RESULTS

The diagnosis of HS of the ileum with secondary nodal and cardiac metastatization was made.

CONCLUSIONS

A prompt diagnosis of HS in life is paramount because it can make a difference in prognostic outcomes.

Vascular Tumors of Bone: Updates and Diagnostic Pitfall

Vascular tumors of bone can be diagnostically challenging because of their rarity and histologic overlap with diverse mimics. Vascular tumors of bone can be categorized as benign (hemangioma), intermediate-locally aggressive (epithelioid hemangioma), intermediate-rarely metastasizing (pseudomyogenic hemangioendothelioma), and malignant (epithelioid hemangioendothelioma and angiosarcoma). Recurrent genetic alterations have been described, such as FOSB rearrangements in pseudomyogenic hemangioendothelioma and a subset of epithelioid hemangiomas; CAMTA1 or TFE3 rearrangements in epithelioid hemangioendothelioma. This review discusses the clinical, histologic, and molecular features of vascular tumors of bone, along with diagnostic pitfalls and strategies for avoidance.

Successful Treatment of Incidental Histiocytic Sarcoma Concomitant with Laryngeal Carcinoma

Histiocytic sarcoma (HS) is an extremely rare non-Langerhans cell disorder with an aggressive course and limited treatment options. HS most often presents at an advanced clinical stage, with a limited response to chemotherapy and high mortality. No standard treatment has been established for HS. We herein describe the first case of HS concomitant with laryngeal carcinoma that was promptly diagnosed and successfully treated; the condition of the patient has remained stable for 4 years with no recurrence.

Small bowel and lung histiocytic sarcoma revealed by acute peritonitis: A case report with review of literature

INTRODUCTION AND IMPORTANCE

Histiocytic sarcoma (HS) is a rare malignant neoplasm showing morphologic and immunohistochemical features of histiocytes. It is characterized typically by extranodal presentation and a poor clinical course, particularly in cases with disseminated disease.

CASE PRESENTATION

This report documents a case of bifocal and aggressive HS in small bowel and lung revealed by acute peritonitis in a 63-year-old man.

CLINICAL DISCUSSION

Despite its rarity, we believe that the correct diagnosis of HS is crucial for clinical treatment and prognostic prediction.

CONCLUSION

The collection of additional cases of HS are important to obtain further progress in prognosis and guide treatment decisions.

An advanced case of gastric histiocytic sarcoma treated with chemotherapy and gastrectomy: a case report and review of literature

Histiocytic sarcoma is a relatively new disease category and the gastrointestinal origin is sporadic. We report a case of a 74-year-old woman who underwent chemotherapy and proximal gastrectomy for extremely rare, advanced gastric histiocytic sarcoma. The resected specimen was subjected to numerous immunostainings to meet the diagnostic criteria of histiocytic sarcoma and was positive for the histiocyte markers' cluster of differentiation 68 and lysozyme. The markers of Langerhans cells, follicular dendritic cells, and myelocyte were all negative. Six reports of surgical resection of histiocytic sarcoma originating in the stomach exist, including our case. We reviewed the clinical course and the histological and immunohistochemical diagnostic features of surgically resected gastric histiocytic sarcoma.

Spindle-cell (Sarcomatoid) Variant of Cutaneous Anaplastic Large-cell Lymphoma (C-ALCL): An Unusual Mimicker of Cutaneous Malignant Mesenchymal Tumors-A Series of 11 Cases

Cutaneous anaplastic large-cell lymphoma (C-ALCL) represents one of the entities within the group of CD30-positive lymphoproliferative disorders of the skin. Most cases are ALK-negative, though isolated cases of ALK-positive C-ALCL have also been reported. By definition, the diagnosis of C-ALCL requires the expression of CD30 in >75% of the cells. Histopathologically, C-ALCL shows a dermal-based nodular and circumscribed proliferation of large pleomorphic cells with vesicular nuclei, prominent nucleoli, and eosinophilic cytoplasm, including hallmark cells. Since 1990, isolated case reports of a so-called "sarcomatoid" variant have been published in the literature. Herein, we present a series of 11 cases of spindle (sarcomatoid) C-ALCL, with comprehensive histopathologic, immunophenotypic, and molecular data. Spindle C-ALCL represents a potential mimicker of malignant mesenchymal or hematopoietic tumors in the skin and should always be considered in the differential diagnosis when assessing cutaneous pleomorphic spindle cell neoplasms.

Recent Advances in Digestive Tract Tumors: Updates From the 5th Edition of the World Health Organization "Blue Book"

CONTEXT.—

The World Health Organization Classification of Tumours: Digestive System Tumors, 5th edition, was published in 2019 and shows several impactful changes as compared with the 4th edition published in 2010. Changes include a revised nomenclature of serrated lesions and revamping the classification of neuroendocrine neoplasms. Appendiceal goblet cell adenocarcinoma is heavily revised, and intrahepatic cholangiocarcinoma is split into 2 subtypes. New subtypes of colorectal carcinoma and hepatocellular carcinoma are described. Precursor lesions are emphasized with their own entries, and both dysplastic and invasive lesions are generally recommended to be graded using a 2-tier system. Hematolymphoid tumors, mesenchymal tumors, and genetic tumor syndromes each have their own sections in the 5th edition. New hematolymphoid lesions include monomorphic epitheliotropic intestinal T-cell lymphoma; duodenal-type follicular lymphoma; intestinal T-cell lymphoma, not otherwise specified; and indolent T-cell lymphoproliferative disorder of the gastrointestinal tract. This paper will provide an in-depth look at the changes in the 5th edition as compared with the 4th edition.

OBJECTIVE.—

To provide a comprehensive, in-depth update on the World Health Organization classification of digestive tumors, including changes to nomenclature, updated diagnostic criteria, and newly described entities.

DATA SOURCES.—

The 5th edition of the World Health Organization Classification of Tumours: Digestive System Tumours, as well as the 4th edition.

CONCLUSIONS.—

The World Health Organization has made many key changes in its newest update on tumors of the digestive system. Pathologists should be aware of these changes and incorporate them into their practice as able or necessary.

Histiocytic sarcoma arising from a lymph node: a diagnostic conundrum

Histiocytic Sarcoma (HS) is extremely rare, with only a few hundred cases reported in the literature. The majority of patients present with symptoms due to unifocal or multifocal extra-nodal disease. Less than 20% of these cases show solitary involvement of a lymph node. We report a case of a solitary HS in a 53-year-old woman presenting with a 2.7-cm right groin mass arising from an inguinal lymph node. The initial cytologic examination of the tissue showed a high-grade spindle-shaped morphology with high-grade mitotic activity. A high-grade sarcoma was initially considered considering the absence of normal lymphoid aggregate and the presence of high-grade cytologic features in the cells. To evaluate the tumor in its entirety, the mass was surgically excised. A histological examination of the tumor showed focal rimming of the lymphoid tissue at the periphery and a centrally located stellate necrotic focus. The tumor cells had an epithelioid to spindle cell morphology along with large uniform nuclei and prominent nucleoli. A high mitotic index was present. Immunohistochemistry (IHC) stains showed strong positivity for CD68, CD163, and Vimentin, and were weakly positive for SMA and CD45. Based on the histologic and clinical examination, a diagnosis of HS was made. Multiple malignancies can mimic HS histopathology and the rarity of this tumor makes the diagnosis more challenging. No fine-needle aspiration (FNA) criteria for its diagnosis have been recognized. Herein, we report a rare case of an isolated HS involving a lymph node which resembled high-grade sarcoma on the FNA biopsy to raise awareness among our surgical pathologist colleagues.

Histiocytic and Dendritic Cell Sarcomas of Hematopoietic Origin Share Targetable Genomic Alterations Distinct from Follicular Dendritic Cell Sarcoma

Background

Histiocytic and dendritic cell neoplasms are a diverse group of tumors arising from monocytic or dendritic cell lineage. Whereas the genomic features for Langerhans cell histiocytosis and Erdheim‐Chester disease have been well described, other less common and often aggressive tumors in this broad category remain poorly characterized, and comparison studies across the World Health Organization diagnostic categories are lacking.

Methods

Tumor samples from a total of 102 patient cases within four major subtypes of malignant histiocytic and dendritic cell neoplasms, including 44 follicular dendritic cell sarcomas (FDCSs), 41 histiocytic sarcomas (HSs), 7 interdigitating dendritic cell sarcomas (IDCSs), and 10 Langerhans cell sarcomas (LCSs), underwent hybridization capture with analysis of up to 406 cancer‐related genes.

Results

Among the entire cohort of 102 patients, CDKN2A mutations were most frequent across subtypes and made up 32% of cases, followed by TP53 mutations (22%). Mitogen‐activated protein kinase (MAPK) pathway mutations were present and enriched among the malignant histiocytosis (M) group (HS, IDCS, and LCS) but absent in FDCS (72% vs. 0%; p < .0001). In contrast, NF‐κB pathway mutations were frequent in FDCSs but rare in M group histiocytoses (61% vs. 12%; p < .0001). Tumor mutational burden was significantly higher in M group histiocytoses as compared with FDCSs (median 4.0/Mb vs. 2.4/Mb; p = .012). We also describe a pediatric patient with recurrent secondary histiocytic sarcoma treated with targeted therapy and interrogated by molecular analysis to identify mechanisms of therapeutic resistance.

Conclusion

A total of 42 patient tumors (41%) harbored pathogenic mutations that were potentially targetable by approved and/or investigative therapies. Our findings highlight the potential value of molecular testing to enable precise tumor classification, identify candidate oncogenic drivers, and define personalized therapeutic options for patients with these aggressive tumors.

Implications for Practice

This study presents comprehensive genomic profiling results on 102 patient cases within four major subtypes of malignant histiocytic and dendritic cell neoplasms, including 44 follicular dendritic cell sarcomas (FDCSs), 41 histiocytic sarcomas (HSs), 7 interdigitating dendritic cell sarcomas (IDCSs), and 10 Langerhans cell sarcomas (LCSs). MAPK pathway mutations were present and enriched among the malignant histiocytosis (M) group (HS, IDCS, and LCS) but absent in FDCSs. In contrast, NF‐κB pathway mutations were frequent in FDCSs but rare in M group histiocytosis. A total of 42 patient tumors (41%) harbored pathogenic mutations that were potentially targetable by approved and/or investigative therapies.

Histiocytic and dendritic cell neoplasms are a diverse group of tumors arising from the monocytic or dendritic cell lineage. This article presents the molecular characteristics of the four major subtypes of malignant histiocytic and dendritic cell neoplasms, focusing on genomic alterations that could represent therapeutic targets.

Histiocytic Sarcoma Arising From a Long Bone: Report of Two Cases

Histiocytic sarcoma is a rare, but aggressive malignant neoplasm of monocyte/macrophage lineage with a wide age distribution. Bone involvement is exceedingly rarer compared to the lymph node, skin, and soft tissue, and no long bone involvement has been reported in the English literature. We here report 2 cases of histiocytic sarcoma involving the long bone: one from the femur of a 77-year-old female, status post the placement of an intramedullary nail for subtrochanteric hip fracture; the other from the radius of a 3-year-old female with no significant medical history. Radiologic imaging showed highly destructive lesions in both cases with soft-tissue extension. Microscopy in both cases showed sheets of polygonal mononuclear cells with abundant eosinophilic cytoplasm, prominent nucleoli, and frequent mitosis. Hemophagocytosis were also identified. Immunohistochemistry showed that the lesional cells were strongly diffusely positive for CD68 and CD163. The first patient deteriorated rapidly, despite the aggressive treatment of amputation and chemotherapy. However, the second patient is disease free 36 months post the treatment of amputation only. We conclude that the long bone could be the primary site of histiocytic sarcoma. Its prognosis could be very variable and it is difficult to predict its behavior based on morphological evaluation only.

A Rare Case of Histiocytic Sarcoma Secondary to Gastrointestinal Stromal Tumor in the Stomach: Transdifferentiation or Synchronicity?

Histiocytic sarcoma is a rare malignant histiocytic neoplasm composed of cells with morphologic and immunophenotypic features of mature tissue histiocytes. It occurs anywhere in the body and behaves aggressively. However, its etiology is unknown. Here, we report a 68-year-old female who developed histiocytic sarcoma following chemotherapy with imatinib (Gleevec) for gastrointestinal stromal tumor. Possible mechanisms of transdifferentiation from gastrointestinal stromal tumor to histiocytic sarcoma are discussed based on the features of our case and other two similar cases in the literature.

Overview of Gastrointestinal Lymphoproliferative disorders✰

Lymphoproliferative processes which occur in the gastrointestinal tract range from benign reactive processes such as follicular hyperplasia (rectal tonsil) to high grade malignant lymphomas and histiocytic sarcoma. The WHO Classification of Tumors: Digestive System Tumors, 5th Edition was published in 2019 and shows several impactful changes as compared to the 4th Edition published in 2010. WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues 2017 also included detailed changes in hematopoietic neoplasms within the gastrointestinal tract. New entities or renamed hematolymphoid lesions include monomorphic epitheliotropic intestinal T-cell lymphoma, duodenal-type follicular lymphoma, intestinal T-cell lymphoma, NOS and indolent T-cell lymphoproliferative disorder of the gastrointestinal tract. A brief overview of WHO classification of digestive tumors and WHO classification of tumors of hematopoietic and lymphoid tissue is discussed focusing on the changes in the most recent WHO texts. In depth discussions will be presented in other papers in this series.

Normal gastrointestinal tract inflammatory cells and review of select benign hematolymphoid proliferations

The luminal gastrointestinal tract can be a site of robust immune response in which reactive lymphoproliferative processes can sometimes be difficult to distinguish from lymphoma. In this article, we review gastrointestinal tract normal resident inflammatory cells and common nonneoplastic lymphoproliferative responses with emphasis on their differential and links to lymphoma. Topics that are covered include lymphocytic esophagitis, gastric chronic inflammation, mucosa-associated lymphoid tissue, and ulceration, small intestinal lymphoid hyperplasia, celiac disease, microscopic colitis, inflammatory bowel disease, primary immunodeficiency, graft-versus-host disease, and anti-programmed cell death protein-1 effect. We additionally present the less common differential of histiocytic processes within the gastrointestinal tract. The aim of this paper is to serve as a reference for practicing pathologists facing lymphoid, lymphoplasmacytic, or histiocytic processes in the luminal gastrointestinal tract. We hope to help the practicing pathologist distinguish benign from malignant entities and identify features requiring further workup.

Histiocytic Sarcoma: Challenging Course, Dismal Outcome

Histiocytic sarcoma (HS) is a rare hematopoietic neoplasm derived from non-Langerhans histiocytic cells of the monocyte/macrophage system. With an incidence of 0.17/million individuals and a slight male preference, HS presents with a wide age distribution. Most commonly, it occurs as a primary malignancy. In approximately 25% of the cases a presumed transdifferentiation of a preexisting hematolymphoid disorder can be demonstrated. The clinical presentation varies from a localized solitary mass to severe disseminated disease often with extranodal involvement including skin, soft tissue, the gastrointestinal tract and the hematopoietic system. Systemic symptoms in terms of weight loss, fever and night sweats often occur. The diagnostic work-up of HS is extremely challenging due to the rarity of the disease as well as a wide differential diagnosis in terms of a histologic overlap with diverse mimics. No standardized treatment for HS exists and especially in a disseminated disease the clinical course is overly aggressive with a dismal outcome. The median overall survival from the time of diagnosis is approximately six months. We report a 43-year-old previously healthy Caucasian male admitted to our hospitals with abdominal pain and a feeling of fatigue. We demonstrate both the challenges of a correct diagnosis and an effective treatment as well as the aggressive nature of histiocytic sarcoma.

Cutaneous Histiocytic Sarcoma With Cellular Cannibalism

Cutaneous histiocytic sarcoma (HS) is a rare malignant tumor. An 82-year-old woman presented with a 4 × 2-cm irregular-shaped red nodule on the left posterior scalp. A biopsy specimen revealed sheets of pleomorphic atypical cells in the dermis and subcutis. A diagnosis of HS was made based on the results of a panel of immunohistochemical stains that revealed positivity of leukocyte common antigen, CD4, CD163, and HLA-DR. At the time of resection, the tumor grew rapidly to 12 × 6.5 × 5 cm in size in 2 months. The resected tumor comprised round, oval, plasmacytoid, and spindled cells. Signet-ring cell type tumor cells were also observed. The histiocytic nature of HS was confirmed owing to the presence of cellular cannibalism, emperipolesis, Langhans giant cell-like cells, Touton giant cell-like cells, foreign-body giant cell-like cells, and hemosiderin laden cells. In some foci, a storiform pattern and fascicular pattern were occasionally observed. Local recurrence occurred shortly after resection. Subsequent radiation therapy showed insufficient effectiveness. It is challenging to make a diagnosis of HS without performing immunohistochemical studies; however, a variety of histiocytic features confirmed in hematoxylin and eosin-stained sections may suggest HS.

A metastatic histiocytic sarcoma case with primary involvement of the tonsil

Histiocytic sarcoma (HS) is an extremely rare and aggressive hematopoietic tumor. Although it can be seen at any anatomic location, the most common primary sites are skin as extranodal region, locations including the lymph nodes and gastrointestinal tract. To the best of our knowledge, in light of PubMed search, this is the first primary tonsillar HS case presented with disseminated metastases at the time of diagnosis. A 58-year-old male patient applied with swelling on the right side of the neck, difficulty in swallowing, and weight loss. Positron emission tomography computed tomography was performed and increased pathological 18F fluorodeoxy D glucose uptake was detected in the right palatine tonsil, bilateral cervical multiple lymph nodes, liver masses, intra abdominal lymph nodes, and nodular lesion in the left adrenal gland. Tonsillectomy was performed and the pathological result was reported as HS. The patient did not respond to any treatment and had died after 5 months from the date of diagnosis. In conclusion, HS is generally diagnosed at advanced stage, it has limited chemotherapy response and high mortality rates. To understand this rare disease's pathophysiological and clinical features, further investigations are needed.

Leukemic Phase of Histiocytic Sarcoma of the Digestive System: A Rare Manifestation of a Rare Disease

Histiocytic sarcoma (HS) is a rare, malignant, and aggressive subtype of histiocytosis. We present an unusual case of aggressive HS presenting in the gastrointestinal tract and gallbladder that progressed after several lines of chemotherapy with a leukemic phase. We review the clinical, pathological, and molecular characteristics of HS in this case and review the literature on HS involving the digestive system as well as on overt leukemic phase of this disease. HS is often diagnosed at an advanced stage, and mortality is high. We discuss the therapeutic approach to patients with HS. We highlight the role of overexpression and somatic alterations in the RAF-MEK-ERK pathway in the pathogenesis of HS and discuss potential targeted approaches to treat these rare tumors.

Descriptive Analysis of Histiocytic and Dendritic Cell Neoplasms: A Single-Institution Experience

PURPOSE

Histiocytic and dendritic cell neoplasms are rare hematologic tumors. This study aimed to describe the epidemiologic features of the entire spectrum of histiocytic and dendritic cell neoplasms, including clinicopathological variables and patient outcomes.

MATERIALS AND METHODS

We comprehensively reviewed 274 patients who were diagnosed with histiocytic and dendritic neoplasms at Severance Hospital, Seoul, South Korea between 1995 and 2018.

RESULTS

The most common neoplasm was Langerhans cell histiocytosis (LCH), followed by dermal xanthogranuloma. Among non-LCH sarcomas, histiocytic sarcoma (HS) showed a relatively high prevalence, followed by follicular dendritic cell sarcoma (FDCS). Disseminated juvenile xanthogranuloma (DJG), Erdheim-Chester disease (ECD), indeterminate dendritic cell tumor (IDCT), and interdigitating dendritic cell sarcoma (IDCS) rarely occurred. Generally, these tumors presented in childhood, although the non-LCH sarcoma (HS/FDCS/IDCS/IDCT) group of tumors and ECD occurred in late adulthood. Multiorgan involvement and advanced Ann-Arbor stage, as well as recurrence and death of disease, were not uncommon. The non-LCH sarcoma group had the worst overall survival, compared to the DJG, ECD, and LCH groups.

CONCLUSION

Our findings indicate that histiocytic and dendritic cell neoplasms exhibit heterogeneous epidemiologic characteristics and that some patients may have unfavorable outcomes, especially those with non-LCH sarcoma.

Primary Histiocytic Sarcoma in Adult Polycystic Kidney Disease: Case Report and Review of Literature

Genetically driven tissue destruction followed by remodeling in adult polycystic kidney disease (APKD) raises the possibility of malignant transformation. Renal cell carcinoma (RCC) associated with APKD has been frequently reported in the literature; however, only a few cases of nonepithelial neoplasms arising in APKD have been described so far. Histiocytic sarcoma (HS) is a lymphohematopoietic malignant neoplasm that accounts for less than 1% of hematologic malignancies. In this article, we describe a case of primary HS occurring in a 61-year-old man with end-stage renal disease secondary to APKD. This is the first reported case of primary HS in the setting of APKD. The aberrant h-caldesmon expression seen in this case is another novel finding that has previously not been described. This case highlights the importance of morphology in guiding diagnostic workup and reiterates the necessity of maintaining a high index of suspicion for neoplastic entities in APKD.

A case of spindle cell dominant histiocytic sarcoma showing a complete remission after first-line chemotherapy with doxorubicin and ifosfamide

Histiocytic sarcoma (HS), an extremely rare malignancy, usually follows a progressive time course, and patients die within two years of diagnosis. At present, there is no consensus for effective chemotherapy. We report the case of a 54-year-old man who presented with low back pain and left hip joint pain. Imaging for the pain revealed multiple lesions in the mediastinum, vertebral bodies, and left ilium. Biopsies of the mediastinal and vertebral lesions yielded a diagnosis of soft tissue sarcoma. He received standard chemotherapy for sarcoma with doxorubicin and ifosfamide, as the initial pathological diagnosis was soft tissue sarcoma. This is called AI therapy and commonly used for soft tissue sarcoma. Palliative radiation therapy to the left iliac lesion was added for pain control. Complete remission (CR) was achieved after two courses of AI therapy. Subsequent immunopathological examination revealed that the tumor was spindle cell dominant HS. CR was maintained for more than three years. To the best of our knowledge, this is the first report that a CR was achieved by AI therapy as first-line treatment for spindle cell dominant HS, combined with focal bone palliative irradiation. AI therapy could be an effective option as chemotherapy for HS.

Practical Approaches on CD30 Detection and Reporting in Lymphoma Diagnosis

While our understanding of the biology of CD30 in lymphoma continues to evolve, our need to detect and measure its expression at the protein level remains critically important for diagnosis and patient care. In addition to its diagnostic and prognostic utility, CD30 has emerged as a vehicle for drug targeting through the antibody-drug conjugate brentuximab-vedotin (BV). Given the numerous ways that CD30 is utilized and its emergence as a predictive/prognostic biomarker, pathologists must come to a general consensus on the best reporting structure and methodology to ensure appropriate patient care. In this manuscript, we review the indications for testing, various modalities for testing, technical challenges, pitfalls, and potential standards of reporting. The following questions will try to be addressed in the current review article: What defines a "POSITIVE" level of CD30 expression?; How do we evaluate and report CD30 expression?; What are the caveats in the evaluation of CD30 expression?