Intrahepatic cholangiocarcinoma (iCCA) is histologically classified into the small duct type (SDT) and large duct type (LDT), although their morphological differential diagnosis can be difficult. We aimed to identify new immunohistochemical markers to classify SDT and LDT with high sensitivity and specificity. We compared the gene expression profiles of SDT and LDT using cases obtained from our institution (n = 8) and The Cancer Genome Atlas database (n = 28). We selected the candidate molecules that were up-regulated in LDT, were minimally or not expressed in SDT, and had specific and available antibodies suitable for immunohistochemistry. We finally selected ST6 N-acetylgalactosaminide alpha-2,6-sialyltransferase 1 (ST6GalNAc1), Breast carcinoma amplified sequence-1 (BCAS-1), and Olfactomedin 4 (OLFM4), which were expressed in 100%, 100%, and 98.3% of 58 LDT cases, respectively. ST6GalNAc1 was expressed in 3.8% of 52 SDT cases, whereas BCAS-1 and OLFM4 were expressed in 48.1% and 34.6% of SDT cases, respectively. ST6GalNAc1 was also expressed in intraductal papillary neoplasm of the bile duct (100%, n = 17) and only the adenocarcinoma component corresponding to LDT among the combined hepatocellular-cholangiocarcinoma cases (100%), but not in hepatocellular carcinoma (n = 26). In small biopsy specimens, ST6GalNAc1 was expressed in 100% of LDT (n = 18) and 12.5% of SDT (n = 16) samples. ST6GalNAc1 expression was associated with significantly shorter overall survival (P = 0.012) and remained significant after adjustment for tumor subtype (hazard ratio 2.595; 95% confidence interval, 1.433-4.699; P = 0.002). ST6GalNAc1 is useful for iCCA subtype identification with high sensitivity and specificity, showing promise to become a more powerful tool when combined with other markers.

Extensive myocardial disarray is a characteristic histopathological feature of hypertrophic cardiomyopathy (HCM), but its occurrence in hearts with normal cardiac mass remains poorly characterized. We reviewed 2,823 consecutive forensic autopsies and identified 1,387 hearts with normal cardiac weight. Ten cases (0.72%) demonstrated extensive type Ia myocardial disarray involving contiguous myocardial regions. Histopathological findings, clinical information, and genetic data were analyzed, and matched controls (n = 20) were selected for comparison. Disarray was accompanied by moderate-to-severe fibrosis and small intramural arterial abnormalities. Three individuals fulfilled criteria for sudden cardiac death, and none had been diagnosed with HCM during life. Matched controls lacked comparable disarray and demonstrated significantly less fibrosis. Genetic analysis identified rare variants in cardiomyopathy-associated genes, although most were classified as variants of uncertain significance. Extensive myocardial disarray and fibrosis can occur in hearts with normal cardiac mass. Although these findings do not establish a diagnosis of HCM, they define a concealed cardiomyopathic phenotype with histological overlap with HCM. Recognition of such abnormalities may improve pathological evaluation of sudden death cases currently classified as structurally normal at autopsy.

Uterine tumour resembling ovarian sex cord tumour (UTROSCT) is an uncommon neoplasm associated with recurrent gene fusions involving NCOA1-3, with ESR1 and GREB1 being the most frequent fusion partners. Fusions are not present in all cases and there have been few reports of gene mutations in these neoplasms. We report an index case of a UTROSCT (classic morphology with supportive immunophenotype) in a 58-year-old woman with no demonstrable fusions on RNA next generation sequencing (NGS) but with CTNNB1 and PTEN gene mutations. We reviewed a large series (n = 28) of UTROSCT from a single institution which had undergone RNA and DNA NGS. A total of 26 gene mutations were found in 12 of 28 (43%) cases, although no highly recurrent mutations were present. In 8 of these 12 cases, there were also characteristic gene fusions of UTROSCT. We stress that, especially in cases of UTROSCT with no fusions identified on RNA sequencing, it may be useful and informative to undertake DNA testing to look for underlying mutations.

Endometrial carcinoma (EC) is a common gynecological cancer with rising incidence driven by obesity and aging populations. Accurate and timely molecular classification is critical for guiding personalized oncology treatment, especially in early-stage high-grade endometrioid carcinoma. Here we present a large scale, retrospective multicenter validation of a novel POLE-POLD1 mutation assay for use in molecular characterization of EC. We evaluated the analytical performance and robustness of the novel Idylla™ POLE-POLD1 Mutation Assay, a cartridge-based PCR platform optimized for FFPE tissue. Performance comparators were established NGS reference methods. Overall, 544 formalin-fixed, paraffin embedded (FFPE) EC cases from diagnostic pathology of ten centers in Europe and North America were included. Of 544 samples, 520 revealed POLE-POLD1 test and comparator results, yielding an overall concordance of 97% (PPA of 0.96 and NPA of 0.98). Discordance was limited to a small number of variants and was often associated with low input material or the detection of multiple concurrent variants. The assay demonstrated robust performance across variable FFPE slice thickness (4-10 μm), number of Sects. (1-6), and tumor cell percentage (from 10% to 100%), with an assay invalid rate of only 2.76%. Moreover, the Idylla™ platform offers rapid results (~ 2 h) with minimal workflow complexity. The Idylla™ POLE-POLD1 Mutation Assay is a reliable and rapid diagnostic assay for clinically relevant molecular classification of EC, demonstrating high concordance with NGS and robust performance under routine pathology conditions. Whereas NGS provides comprehensive genomic profiling, including rare variants of unknown pathogenic significance, the Idylla™ assay targets treatment relevant pathogenic variants with rapid turnaround time, supporting timely, individualized treatment decisions.

SMARCB1/INI1-deficient peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), is a rare entity with limited reported cases. We present two additional cases in young women presenting with aggressive, treatment-refractory PTCL-NOS, and further characterizing their clinicopathologic and molecular features. Both cases demonstrated a monotonous proliferation of medium-sized atypical αβ T cells with clear cytoplasm, dual CD4/CD8 negativity, aberrant CD117 expression, cytotoxic and PTCL-TBX21 phenotype, and loss of SMARCB1/INI1 expression. Molecular analyses revealed copy-neutral loss of heterozygosity and two-copy/homozygous deletion involving the SMARCB1 gene, supporting a heterogeneous genetic basis for SMARCB1 inactivation. Clinically, both patients exhibited rapidly progressive disease with poor response to multi-modality treatment, highlighting the aggressive nature of this tumor. Our findings are consistent with prior reports, suggesting that SMARCB1/INI1-deficient PTCL-NOS preferentially affects children and young adults and demonstrates distinctive morphologic and molecular features that may facilitate recognition. Emerging evidence also indicates that SMARCB1/INI1 loss may confer sensitivity to histone deacetylase inhibitors (HDACi), supporting their potential therapeutic role in this tumor. Given the dismal outcomes associated with this entity, assessment of SMARCB1/INI1 expression should be considered in younger patients with PTCL-NOS displaying these characteristic features. Continued accumulation of cases with integrated molecular profiling, along with prospective evaluation of HDACi-based therapies, will be essential to better define disease biology and establish evidence-based treatment strategies for this aggressive lymphoma.

The characterization of DICER1-associated thyroid disease has expanded in recent years, leading to growing interest in the morphological findings that may suggest an underlying DICER1 alteration. In this regard, atrophic changes (ACs) are nodular sclero-atrophic areas with flattened follicles that have emerged as a promising specific finding. However, their role is not yet universally recognized. Similarly, there is little experience with the use of an anti-DICER1 monoclonal antibody. This report describes a 56-year-old woman with sporadic thyroid follicular nodular disease (multinodular goiter), in whom only one of multiple nodules showed ACs, strong DICER1 immunoreactivity and a classic double somatic DICER1 hit. This observation further supports the potential value of ACs, complemented by DICER1 immunohistochemistry, in identifying the specific thyroid nodule most likely to harbor DICER1 alterations and therefore to be prioritized for molecular testing.

Borderline breast lesions (B3 lesions, also termed lesions of uncertain malignant potential or high-risk lesions) represent a heterogeneous group of entities associated with variable risks of malignancy. While the management of screen-detected B3 lesions has become increasingly standardised, no dedicated international recommendations exist for symptomatic B3 lesions, despite them posing a distinct clinical challenge. Symptomatic lesions differ from screen-detected lesions in their mode of presentation, lesion characteristics, biopsy techniques, and diagnostic objectives; consequently, management strategies derived from screening populations may not be directly applicable. This review summarises the current evidence and proposes a pragmatic management framework for B3 lesions encountered in the symptomatic setting (defined as those presenting with breast symptoms outside population-based screening programmes). This is particularly relevant for patients under 50 years of age, where the primary objective is to exclude malignancy at the index site rather than solely to stratify long-term cancer risk. Clinical-radiological-pathological concordance and multidisciplinary assessment are central to management decisions. Lesions presenting as palpable abnormalities (which are typically larger) or those demonstrating radiological-pathological discordance warrant a lower threshold for additional sampling or excision. Conversely, selected concordant lesions without atypia may be managed conservatively following adequate sampling. The long-term cancer risk associated with epithelial atypia should also be considered with subsequent risk-based surveillance implemented where appropriate. Overall, management requires a risk-adapted, multidisciplinary approach integrating pathological, radiological, and clinical factors alongside patient symptoms and quality-of-life considerations. Given the limited evidence, current recommendations rely on expert consensus and a proposed practical framework. They underscore the need for large-scale, high-quality studies with long-term follow-up to establish formal clinical guidelines.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, aggressive precursor cell hematological malignancy with a dismal prognosis, necessitating prompt and accurate diagnosis. However, its blastoid morphology and immunophenotype may lead to diagnostic confusion with a broad spectrum of hematological neoplasms. This systematic review delineates the critical morphological, immunophenotypic, and molecular features required to distinguish BPDCN from its mimics across common sites of involvement (skin, bone marrow, and lymph nodes). We reinforce the diagnostic criteria for BPDCN and provide an in-depth analysis of its differential diagnosis, structuring it into two groups: (A) hematological neoplasms with blastoid morphology (e.g., ALL/LBL, blastoid MCL, AML, myeloid sarcoma), and (B) myeloid malignancies with pDC-associated markers (e.g., AML with pDC-like phenotype, AML with pDC expansion, mature pDC proliferation). We emphasize the integration of immature and lineage-specific markers, and molecular data (e.g., ZRSR2, MYB/MYBL1, NPM1, FLT3, RUNX1, DNMT3, CCND1 status) to resolve diagnostic dilemmas. The aim is to provide a comprehensive diagnostic review and guide to standardize the workup and facilitate the early initiation of appropriate treatment for this challenging disease.

The evaluation of tumors is increasingly becoming an integrated diagnosis based on combined histologic and genomic evaluations. As more tumors are subjected to genomic analyses, discrepancies between the histologic diagnosis and molecular findings surface. Pathologic review of genomic-directed specimens plays a vital role in understanding and resolving these discrepancies. We aim to assess the frequency of and reasons for discrepant diagnoses in genomic-directed specimens from a precision genomics program. A retrospective review of genomic-directed specimens analyzed through a precision genomics program was performed. We assessed the frequency of discrepancies between the histologic diagnosis and molecular findings. The discrepant cases were further studied to uncover the reasons behind the discrepancy. 381 patients referred to the program had their tumors sequenced. Nine cases (2.4%) had discrepancies between the original histologic diagnosis and molecular findings. These discrepancies were related to a combination of nonspecific morphology, nonconclusive immunophenotypes, and misleading immunophenotypes. While infrequent, diagnostic discrepancies do occur in genomic-directed specimens. These cases are often diagnostically challenging to begin with. Integrated diagnostics (histology, immunohistochemistry, and molecular) and collaborative discussions are critical for resolving and reducing discrepancies.

Desmoplastic reaction (DR), characterised by myxoid stroma and keloid-like collagen, is a poor prognostic factor in several types of cancer. We investigated the impact of stromal DR status on recurrence and prognosis in patients with upper urinary tract urothelial carcinoma (UTUC). This study included 155 UTUC patients who underwent surgery between 1999 and 2021. The presence of myxoid stroma and keloid-like collagen at the invasive front of the tumour was evaluated. Patients were classified into three groups: mature-type, keloid-like, and myxoid-type DR. We analysed the associations between DR status and clinicopathological factors, tumour budding (BD), and tumour-associated immune cell status (TAICs), as well as its impact on extraurothelial recurrence-free survival (EUR-FS) and overall survival (OS). Among the 155 patients, 101 (65%), 15 (10%), and 39 (25%) were classified as mature-type, keloid-like, and myxoid-type DR, respectively. DR status was significantly associated with adverse pathological prognostic factors. In univariate analysis, higher pathological T category, lymphovascular invasion, lymph node metastasis, positive surgical margins, presence of subtype histology, myxoid-type DR, and high-grade BD were significantly associated with worse EUR-FS. Multivariate analysis revealed that myxoid-type DR (HR = 2.19, p = 0.0279) and high-grade BD (HR = 3.35, p = 0.0008) were independent predictors of EUR-FS. Regarding OS, age ≥ 70, lymphovascular invasion, and myxoid-type DR were independent predictors. The presence of myxoid stroma was associated with adverse prognostic factors and low TAICs and served as an independent predictor of EUR-FS and OS. These findings suggest that myxoid stroma in the invasive front represents a novel and useful pathological prognostic indicator for UTUC.

An elevated Ki-67 proliferation index is a known marker of adverse prognosis in several solid and hematological tumors, but its role in Myelodysplastic Syndromes (MDS) remains underexplored. This study aimed to quantify Ki-67 expression across hematopoietic lineages in bone marrow biopsies (BMB) from MDS patients and assess its correlation with clinical features and outcomes. We performed single and double immunohistochemistry for Ki-67 with CD34, CD71, MPO, and Factor VIII on BMB samples from 73 patients diagnosed with MDS or oligoblastic acute myeloid leukemia (AML) at a single center. The cohort had a median age of 70 years, 56% were male, 81% had de novo MDS, and 15% therapy-related MDS. Abnormal karyotypes were present in 32%, and 52% had International Prognostic Scoring System scores ≥ 3.5. Median overall survival (OS) and progression-free survival (PFS) were 2.8 and 2.7 years, respectively. Ki-67 expression upper 10% occurred in 27% of patients. Coexpression of Ki-67 with CD34, MPO, CD71, and Factor VIII was observed in 79%, 63%, 85%, and 16% of cases, respectively. Notably, coexpression Ki-67 with Factor VIII+ correlated with higher blast counts, shorter PFS (HR 3.29), and reduced OS (HR 2.96). Incorporating Ki-67/Factor VIII double labeling improved prognostic accuracy when added to the IPSS-R model. Ki-67 expression in megakaryocytes is a potential independent prognostic marker that requires validation in larger prospective cohorts and may reflect a bone marrow microenvironment dysregulation.

The growing use of targeted therapies highlights the need for integrated DNA- and RNA-based next-generation sequencing (NGS) to comprehensively profile tumors. A single-center study was conducted to screen tumor types for which a first-line, integrated DNA-RNA NGS strategy provides a valuable advantage for rapid therapeutic decisions. A total of 546 tumor samples, including early- and late-stage lung adenocarcinoma (LUAD), intrahepatic and extrahepatic cholangiocarcinoma (iCCA/eCCA), and glioblastoma were analyzed using an automated, in-house NGS platform. Sequencing success rates ranged from 98.7% to 100%, with a median turnaround time of eight days from sample collection or histological diagnosis to report delivery. The assay simultaneously detected point mutations, gene fusions, copy number variants, and other clinically relevant alterations, even from small tissue samples. In LUAD, EGFR exon 19 deletions and KRAS p.G12C were the most frequent actionable mutations in early- and late-stage disease, respectively. A significant association was observed between EGFR amplification and the presence of actionable EGFR mutations in late-stage tumors. Actionable co-mutations of EGFR or KRAS with TP53 occurred at distinct frequencies, suggesting relevant clinical implications for therapy selection. Mutation profiles in cholangiocarcinoma and glioblastoma were consistent with published data, reinforcing the robustness of the approach. The results demonstrate that integrated DNA-RNA high-throughput NGS enables timely, precise molecular profiling for personalized therapy in solid tumors.