The patient we present here had many clinical, morphological, and laboratory findings characteristic of acute leukemia. During the course of the disease, the diagnosis changed from acute leukemia to chronic small B-cell lymphoproliferative disease, a blastoid variant of mantle cell lymphoma, and finally to atypical plasma cell leukemia. Atypical plasma cell leukemia is a rare condition with aggressive biological behavior. Our patient relapsed a short time after achieving complete remission, in spite of aggressive therapy and autologous stem cell transplantation. During relapse, it was possible to morphologically identify malignant cells as being of plasma cell origin, although immature and atypical. Atypical plasma cell leukemia presents a diagnostic challenge as it may mimic other neoplasms both morphologically and clinically. It is also recognized that plasma cell neoplasm immunophenotype may not be entirely specific for its lineage where common diagnostic biomarkers are applied by immunohistochemistry or flow cytometry. Where this is the case, only focused investigation for plasma cell lineage will be more informative. This patient has unusual clinical presentation, a nondescript morphology of the circulating plasma cells, as well as an immunophenotype, detected by the initial panels used for flow cytometry and immunohistochemistry, that was not entirely specific for plasma cells. Such cases present a good reminder of the diagnostic complexity of atypical plasma cell leukemia and emphasize that plasma cell differentiation needs to be interrogated in cases where the initial work-up shows unusual results.

Multiple myeloma (MM) is an incurable malignant plasma cell neoplasm, representing the second most common hematopoietic cancer. As plasma cell neoplasms are clonal and often secrete a monoclonal protein (M-spike), laboratory diagnosis is usually straightforward, especially when ancillary studies such as immunohistochemistry, flow cytometry, and protein electrophoresis are available in addition to microscopic examination. Despite the repertoire of diagnostic tools, rare cases pose diagnostic dilemmas, especially when reagent antibodies do not react as expected, extent of disease is patchy, or when disease occurs in unique age groups. In this retrospective study, we report a series of challenging diagnostic cases, discussing aberrant findings and comparing them to more classic counterparts. Twelve cases collected during routine clinical sign-out were reanalyzed and include examples of MGUS, classic multiple myeloma, t(11; 14) rearranged myeloma, minimal residual disease, AA and AL amyloidosis, truncated light chain, non-secretory and non-producer myeloma, biphenotypic myeloma, oligoclonal expansion after bone marrow transplant, and plasma cell leukemia in a young adult. This cohort showcases the diversity of atypical presentations of plasma cell neoplasms, and we highlight standardized approaches to workup to avoid diagnostic pitfalls.

Depression is a prevalent and incapacitating condition with a significant impact on global morbidity and mortality. Although the immune system\'s role in its pathogenesis is increasingly recognized, there is a lack of comprehensive understanding regarding the involvement of innate and adaptive immune cells. To address this gap, we conducted a multicenter case-control study involving 121 participants matched for sex and age. These participants had either an active (or current) major depressive episode (MDE) (39 cases) or a remitted MDE (40 cases), including individuals with major depressive disorder or bipolar disorder. We compared these 79 patients to 42 healthy controls (HC), analyzing their immunological profiles. In blood samples, we determined the complete cell count and the monocyte subtypes and lymphocyte T-cell populations using flow cytometry. Additionally, we measured a panel of cytokines, chemokines, and neurotrophic factors in the plasma. Compared with HC, people endorsing a current MDE showed monocytosis (p = 0.001), increased high-sensitivity C-reactive protein (p = 0.002), and erythrocyte sedimentation rate (p = 0.003), and an altered proportion of specific monocyte subsets. CD4 lymphocytes presented increased median percentages of activation markers CD69+ (p = 0.007) and exhaustion markers PD1+ (p = 0.013) and LAG3+ (p = 0.014), as well as a higher frequency of CD4+CD25+FOXP3+ regulatory T cells (p = 0.003). Additionally, patients showed increased plasma levels of sTREM2 (p = 0.0089). These changes are more likely state markers, indicating the presence of an ongoing inflammatory response during an active MDE. The Random Forest model achieved remarkable classification accuracies of 83.8% for MDE vs. HC and 70% for differentiating active and remitted MDE. Interestingly, the cluster analysis identified three distinct immunological profiles among MDE patients. Cluster 1 has the highest number of leukocytes, mainly given by the increment in lymphocyte count and the lowest proinflammatory cytokine levels. Cluster 3 displayed the most robust inflammatory pattern, with high levels of TNFα, CX3CL1, IL-12p70, IL-17A, IL-23, and IL-33, associated with the highest level of IL-10, as well as β-NGF and the lowest level for BDNF. This profile is also associated with the highest absolute number and percentage of circulating monocytes and the lowest absolute number and percentage of circulating lymphocytes, denoting an active inflammatory process. Cluster 2 has some cardinal signs of more acute inflammation, such as elevated levels of CCL2 and increased levels of proinflammatory cytokines such as IL-1β, IFNγ, and CXCL8. Similarly, the absolute number of monocytes is closer to a HC value, as well as the percentage of lymphocytes, suggesting a possible initiation of the inflammatory process. The study provides new insights into the immune system\'s role in MDE, paving the ground for replication prospective studies targeting the development of diagnostic and prognostic tools and new therapeutic targets.

Spontaneous remissions (SRs) in blastic plasmacytoid dendritic cell neoplasms (BPDCNs) are infrequent, poorly documented, and transient. We report a 40-year-old man presenting with bycitopenia and soft tissue infection. The bone marrow exhibited 3% abnormal cells. Immunophenotyping of these cells revealed the antigens CD45+ (dim), CD34+, CD117+, CD123+ (bright), HLA-DR+ (bimodal), CD56+ (bright), CD33+, CD13+, CD2+, and CD22+ (dim) and the partial expression of the CD10+, CD36+, and CD7+ antigens. All other myeloid, monocytic, and lymphoid antigens were negative. Genetic studies showed a complex karyotype and mutations in the TP53R337C and KRASG12D genes. On hospital admission, the patient showed a subcutaneous nodule on the right hand and left lower limb. Flow cytometry multiparameter (FCM) analysis showed the presence of 29% abnormal cells with the previously described immunophenotype. The patient was diagnosed with BPDCN. The patient was treated with broad-spectrum antibiotics for soft tissue infection, which delayed therapy for BPDCN. No steroids or chemotherapeutic or hypomethylating agents were administered. His blood cell counts improved and skin lesions disappeared, until the patient relapsed five months after achieving spontaneous remission. About 60% of abnormal cells were identified. No changes in immunophenotype or the results of genetic studies were observed. The patient underwent a HyperCVAD chemotherapy regimen for six cycles. Consolidation therapy was performed via allogeneic bone marrow transplantation with an HLA-unrelated donor. One year after the bone marrow transplant, the patient died due to the progression of his underlying disease, coinciding with a respiratory infection caused by SARS-CoV-2. In the available literature, SRs are often linked to infections or other stimulators of the immune system, suggesting that powerful immune activation could play a role in controlling the leukemic clone. Nevertheless, the underlying mechanism of this phenomenon is not clearly understood. We hypothesize that the immune system would force the leukemic stem cell (LSC) to undergo a state of quiescence. This loss of replication causes the LSC progeny to die off, resulting in the SR of BPDCN.

BACKGROUND: Paediatric hepatocellular carcinomas (HCC) traditionally arise in the context of a normal structural and functional liver and carry a dismal prognosis. While chemotherapy is the frontline standard, there is emerging interest in the study of immunotherapies for paediatric patients with relapsed/refractory disease. There is limited data to support whether immunotherapies will be of utility in this patient population.
METHODS: Six paediatric patients (median age:16 years, range: 12-17 at the time of treatment) with advanced hepatocellular neosplams, either conventional hepatocellular or fibrolamellar carcinoma, were treated with immunotherapy. Patients were consented to institutional genomic profiling and biobanking protocols. Baseline samples and serial tissue samples, when available, were evaluated for somatic mutation rate, actionable gene mutations, and pan-immune bulk RNA expression profiling. Results were correlated with clinical course.
RESULTS: Three patients responded to checkpoint inhibition: one achieved a complete, durable response and the other two, prolonged stable disease. Three additional patients progressed. Diagnostic tissue from the complete responder demonstrated a higher relative mutational burden and robust immune infiltrate. Pre-treatment samples from the three responders demonstrated decreased expression of genes associated with T-cell dysfunction.
CONCLUSIONS: A subset of patients with primary paediatric hepatocellular tumours will respond to immunotherapy. Immunotherapies are currently under prospective study for relapsed/refractory liver tumours in paediatric patients. Results from this report support the prospective collection of serial serum and tissue samples which may further identify genomic and immunophenotypic patterns predictive of response.
BACKGROUND: This work was supported by Philanthropic funds (Pan Mass Challenge, Team Angus and Team Perspective).

BACKGROUND: Splenic B-cell lymphoma/leukemia with prominent nucleoli (SBLPN) aka hairy cell leukemia variant (HCL-v) is a rare B-cell chronic lymphoproliferative disorder. The main diagnostic challenge is to differentiate SBLPN from Classical hairy cell leukemia (HCL-c), as the former faces inferior responses to therapies and a poor prognosis.
OBJECTIVE: The aim is to discuss the clinic-hematological and immunophenotyping findings of three cases of SBLPN.
METHODS: This is a retrospective observational study.
METHODS: From the year 2011 to 2021, flow cytometry of all the cases with HCL diagnosis was reviewed, and three cases with negative or dim CD25 and hematological presentation matching with SBLPN were picked up.
METHODS: Descriptive statistics is used.
RESULTS: All the cases were male. The age ranges from 43 to 64 years. Median hemoglobin concentration, total leucocyte count, and platelet count were 8.6 g/dL, 6.9 × 109/L, and 53 × 109/L, respectively. The atypical cells were medium to large. All three showed prominent nucleoli. Bone marrow biopsies showed an interstitial pattern of infiltration in all the cases. The hairy cells were positive for CD20, CD11c, and CD103. CD25 was dim positive in one case. Annexin A1 was negative in all three cases. BRAF V600E mutation analysis was done in one case and turned out negative for the mutation.
CONCLUSIONS: SBLPN is a rare entity, usually on-flow cytometry CD25 negative. However, in dim CD25-positive cases, BRAFV600E mutational analysis helps in discerning SBLPN diagnosis and differentiating it from HCL-c.

OBJECTIVE: Mixed-phenotype acute leukemia (MPAL) is a rare disease associated with difficulties in the correct lineage assignment of leukemic cells. One of the least common subtypes within this category is characterized by the simultaneous presence of B- and T-lineage-defining antigens. Each case of suspected B/T MPAL should be considered in light of all available laboratory and clinical data to avoid misdiagnosis.
METHODS: In this study, we describe 6 pediatric patients who presented with leukemic blasts bearing B- and T-lineage antigens at diagnosis, including their clinical, immunophenotypic, morphologic, and cytogenetic characteristics.
RESULTS: In 3 patients, more or less distinct populations of B- and T-lymphoid origin were found; the other 3 patients had a single mixed-phenotype blast population. All cases fulfilled the World Health Organization criteria, but not all of them turned out to be bona fide cases of B/T MPAL according to the available clinical and laboratory data. Found genetic lesions were helpful for the confirmation of MPAL instead of 2 concomitant tumors, but for a general B/T MPAL diagnosis, genetic studies provided the only descriptive data.
CONCLUSIONS: The accurate diagnosis of B/T MPAL requires a multidisciplinary approach combining high-tech laboratory methods and close cooperation between treating physicians and pathologists.

Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) is a rare and aggressive T-cell neoplasm associated with poor survival. We report a case of MEITL that presented as an ulcerated mass in the jejunum with perforation. Microscopic examination showed that the neoplasm involved the full thickness of the intestinal wall, extended into the mesentery, and was composed of monomorphic, small to medium-size cells. Immunohistochemical analysis showed that the neoplastic cells were positive for T-cell receptor (TCR) delta, CD3, CD7, CD8 (small subset), BCL-2 and TIA-1, and negative for TCR beta, CD4, CD5, CD10, CD20, CD30, CD34, CD56, CD57, CD99, ALK, cyclin D1, granzyme B, MUM1/IRF4, and TdT. The Ki-67 proliferation index was approximately 50 %. In situ hybridization for Epstein-Barr virus-encoded RNA (EBER ISH) was negative. Next-generation sequencing (NGS) analysis showed mutations involving SETD2 and STAT5B. The patient was treated with aggressive chemotherapy and consolidative autologous stem cell transplant and had clinical remission, but relapsed after about one year. Retreatment led to another one-year interval of clinical remission, but at last follow up the patient has relapsed disease involving the ileum and colon. We also discuss the differential diagnosis of MEITL.

Interfollicular Hodgkin lymphoma (IHL) has been rarely reported in the literature and is recognized by the WHO Classification as a morphologic pattern sometimes seen in mixed cellularity classic Hodgkin lymphoma (CHL). The changes may be subtle due to preservation of architecture. We report a case of a 9-year-old male with IHL showing preserved follicular architecture but with the presence of interfollicular infiltrates consisting of eosinophils, plasma cells, and Hodgkin-Reed-Sternberg (HRS) cells. Immunophenotyping confirmed the morphologic suspicion for IHL. A discussion and review of the literature are offered. We conclude that IHL is a variant that requires a high index of suspicion, as it may be easily missed due to the subtle morphologic features and preserved architecture seen in most cases. We further emphasize that unexplained interfollicular infiltrates of eosinophils may be clues that should prompt a search of HRS cells and consideration of immunohistochemical staining if needed.

Juvenile primary Sjögren syndrome (pSS) with renal involvement is extremely rare, reported approximately in 50 children, predominantly girls. Here, we present the first reported case of a male child with juvenile pSS with ocular surface disease (previously keratoconjunctivitis sicca), submandibular salivary gland involvement, and tubulointerstitial nephritis. First, two symptoms were clinically apparent at presentation. We illustrate here that kidney involvement in pSS should be actively looked for, as juvenile pSS may be associated with asymptomatic renal involvement. Immunophenotyping of peripheral blood cells using multicolor flow cytometry revealed at the time of diagnosis changes in both adaptive (T memory cells and B memory cells), and innate immunity (an increased activation of natural killer cells, as well as monocytes and neutrophils, and an increased representation of intermediate monocytes). Our case report points to the importance of kidney examination, early diagnosis and therapy in juvenile pSS, as well as highlights international collaboration to obtain more data for this rare disease.