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Recent Advances in Pathology: A Comprehensive Review (2024-2026)

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1. Hematopathology & WHO 5th Edition Updates

General Taxonomy

• Gene fusion nomenclature now uses the HUGO double-colon format (e.g., KMT2A::MLLT3 instead of t(9;11))
• "Provisional entities" replaced by "other defined genetic alterations"
• Morphology alone removed as sufficient diagnostic criteria for AML-MR

Clonal Hematopoiesis

• CHIP (Clonal Hematopoiesis of Indeterminate Potential): somatic mutations (VAF ≥2%, or ≥4% for X-linked genes in males), no cytopenias, no myeloid neoplasm morphology
• CCUS (Clonal Cytopenia of Undetermined Significance): overlapping cytopenias present but not meeting myeloid neoplasm criteria - important pre-malignant surveillance category

Myeloid Neoplasms - New & Renamed Entities

• AML with CEBPA mutation: now includes biallelic (biCEBPA) and single bZIP region mutations (smbZIP-CEBPA)
• AML with mutated TP53: includes separate diagnoses of MDS (0-9% blasts), MDS/AML (10-19%), and AML (>20%) - aggressive behavior regardless of blast count
• Acute erythroid leukemia (AEL): now subsumed under AML with TP53 mutations in ICC
• AML with somatic RUNX1 mutation: no longer a separate entity in WHO5

MDS Reclassification

• MDS subtypes now classified as MDS with low blasts (MDS-LB, <5% BM), MDS-IB1 (5-9% BM), MDS-IB2 (10-19% BM or Auer rods), and MDS with fibrosis (MDS-f)

Myeloid/Lymphoid Neoplasms with Eosinophilia (M/LN-E-TK)

• Myeloid/lymphoid neoplasms with JAK2 rearrangement
• Myeloid/lymphoid neoplasms with FLT3 rearrangement
• Myeloid/lymphoid neoplasms with ETV6::ABL1 fusion

Lymphoid Neoplasms

• New subcategories in mature B-cell, T-cell, NK-cell, plasma cell, and histiocytic/dendritic neoplasms
• EBV-positive DLBCL, NOS receives refined diagnostic criteria and risk stratification framework (PMID 38957951)
• T-cell lymphoma classification significantly restructured with updated molecular correlates - Oishi et al. 2023 review
• JMML reclassified into MPN (WHO) or into pediatric/germline mutation-associated disorders (ICC)

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2. WHO Updates in Other Tumor Types

Breast Tumors - 6th Edition 2026

• HER2 reporting categories updated following DESTINY-Breast 04 and 06 trials - "HER2-low" and "HER2-ultralow" now formally recognized
• New entity: Invasive lobular carcinoma (ILC) with extracellular mucin - distinct prognostic category
• Mucinous carcinoma diagnosis restricted to grade 1-2 morphology with favorable biomarker profile
• Malignant phyllodes tumor now requires only 4 of original 5 adverse criteria
• Neuroendocrine tumor (NET) classification revised; the unified model from the 5th edition is abandoned
• New section on "Small Diagnostic Samples" (B-coding system, non-operative biopsy)
• First dedicated section on Digital Pathology within a WHO Blue Book

CNS Tumors (WHO 5th Edition, 2021)

• IDH status now defines glioma classification: IDH-mutant vs. IDH-wildtype glioblastoma
• TERT promoter, EGFR, and PTEN mutations serve as integrated diagnostic markers in IDH-wildtype GBM
• DNA methylation profiling now a cornerstone of neuropathology - see Al Sharie et al. 2025, Front Oncol (PMID 41487568) - enables simultaneous copy number profiling and tumor classification across diffuse gliomas, medulloblastoma, ependymoma, and meningioma

Salivary Gland Tumors (WHO 2024)

• Secretory carcinoma (with ETV6::NTRK3)
• Sclerosing microcystic adenocarcinoma
• Microsecretory adenocarcinoma

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3. Molecular Pathology

Next-Generation Sequencing (NGS)

• NGS panels are now clinical standard of care for most solid tumors and hematologic malignancies
• Tumor Mutational Burden (TMB) and Microsatellite Instability (MSI) assessed routinely as predictive immunotherapy biomarkers
• Homologous Recombination Deficiency (HRD) testing for PARP inhibitor eligibility in breast/ovarian cancer
• Multi-gene RNA fusion panels replacing single-gene FISH in sarcoma, thyroid, and lung pathology

Liquid Biopsy / Circulating Tumor DNA (ctDNA)

• ctDNA now used for minimal residual disease (MRD) monitoring post-treatment
• Marinello et al. 2024 (PMID 38963991) - ctDNA guides treatment decisions in localized and locally advanced NSCLC
• Methylation-based ctDNA tests (e.g., Galleri multi-cancer early detection test) in active clinical validation
• Fragment length analysis, nucleosome positioning, and copy number from plasma increasingly supplement mutation detection

DNA Methylation Profiling

• Heidelberg classifier for CNS tumors now in routine clinical use at major neuropathology centers
• Nanopore-based rapid methylation testing emerging - potential for near-real-time intraoperative classification
• Extended applications to pituitary tumors: Dottermusch 2025 meta-analysis (PMID 41060331) distinguishes pituitary neuroendocrine tumors from adenomas epigenomically
• Liquid biopsy methylation-based multi-cancer detection expanding beyond CNS

Epigenomics & Multi-omics

• Spatial-ATAC-RNA-seq and spatial-CUT&Tag-RNA-seq (Li et al. 2025, Nat Protoc, PMID 40119005) - simultaneous epigenome + transcriptome mapping in tissue sections
• Single-cell sequencing revealing intra-tumoral heterogeneity with diagnostic and therapeutic implications
• Proteomics integrated with genomics for biomarker discovery (especially HCC per Yu & Ma 2024, PMID 39191624)

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4. Immunohistochemistry (IHC) - New Biomarkers

Companion Diagnostics

• PD-L1 (SP142, 22C3, 28-8, SP263): now required for multiple tumor types; scoring harmonization remains a challenge
• HER2 IHC "ultra-low": grade 0 with incomplete faint staining in <10% cells - new category informing ADC eligibility
• INSM1: emerging neuroendocrine marker with broad applicability, supplementing synaptophysin/chromogranin
• TRPS1: highly sensitive/specific marker for breast lineage (superior to GATA3 in some contexts)
• SOX10: standard marker for nerve sheath and melanocytic differentiation
• NKX2.1 (TTF-1): updated role in lung adenocarcinoma vs. neuroendocrine differentiation

Soft Tissue / Sarcoma IHC Advances

• BCOR IHC: surrogate for BCOR gene alterations in sarcomas
• NUT IHC: highly sensitive for NUT carcinoma - single stain can establish diagnosis
• SMARCA4/SMARCB1 (INI1) loss: expanded diagnostic role across thoracic, renal, and soft tissue tumors
• STAT6 (nuclear): highly specific for solitary fibrous tumor

Predictive Biomarkers

• RET, NTRK, MET (exon 14) IHC: surrogates for molecular testing in NSCLC and thyroid carcinoma
• FGFR IHC: emerging predictive marker for FGFR inhibitor therapy in cholangiocarcinoma and urothelial carcinoma
• Claudin 18.2 IHC: FDA-approved companion diagnostic for zolbetuximab in gastric/GEJ adenocarcinoma (2024)

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5. Digital Pathology

Whole Slide Imaging (WSI) Adoption

• FDA-cleared digital scanners (Leica Aperio GT450, Philips IntelliSite, Hamamatsu Nanozoomer) now form the backbone of clinical digital pathology
• CMS/CLIA issued policies permitting remote primary diagnosis using digital pathology
• New CPT codes for digital pathology introduced, enabling reimbursement workflows
• College of American Pathologists (CAP) validation guidelines establish minimum performance standards

Multimodal & Multiplexed Imaging

• Multiplex IHC/IF (OPAL, CODEX, mIHC): simultaneous 7-10+ markers on a single slide, replacing sequential staining
• MALDI imaging mass spectrometry: spatial proteomics at tissue level
• Imaging mass cytometry (IMC/CyTOF): 40+ simultaneous markers with subcellular resolution
• Expansion microscopy: super-resolution imaging without specialized optics

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6. Artificial Intelligence in Pathology

Current Validated Applications

• Automated prostate cancer detection and Gleason grading (FDA-cleared: Paige Prostate, Ibex Galen Prostate)
• Colorectal cancer detection and polyp classification
• Lymph node metastasis detection
• Cervical cytology screening (fully automated triage)
• Mitosis counting in breast and soft tissue tumors
• Tumor-infiltrating lymphocyte (TIL) quantification

Biomarker Prediction from H&E

• AI models can predict EGFR, KRAS, BRAF, MSI, TMB, HRD, and TP53 status directly from H&E images
• Multi-gene expression subtypes predictable from morphology (e.g., PAM50 in breast cancer)
• Survival/prognosis prediction independent of classical staging in multiple cancers

Foundation Models & Generative AI

• Foundation models (UNI, CONCH, CHIEF, PLIP): large pretrained models fine-tuned for any pathology downstream task - dramatically reducing labeled data requirements
• Virtual staining: AI converts brightfield H&E to IHC-equivalent staining, or unstained tissue to H&E (label-free pathology)
• Synthetic data generation: GAN and diffusion models create realistic synthetic histology for training, augmenting rare tumor datasets
• Large language model (LLM) integration: GPT-4-class models draft pathology reports, extract structured data from free text, and power multimodal diagnostic assistants
• Automated reflex testing: AI triggers molecular/IHC orders based on morphologic findings

AI Limitations & Regulatory Status

• No AI-based prognostic/predictive biomarker currently has Level IA/IB evidence per ESMO
• Challenges: batch effects from different stain protocols, scanner variability, algorithmic bias across demographics
• Regulatory frameworks evolving: FDA oversight for SaMD (Software as a Medical Device), EU AI Act implications for IVD devices
• Explainability ("black box" problem) limiting clinical trust

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7. Laboratory Technology & Automation

Pre-analytical Automation

• Fully automated specimen reception, barcode tracking, accessioning, and grossing assistance (robotic grossing stations)
• Total laboratory automation (TLA) lines integrate specimen processing, centrifugation, aliquoting, and storage
• Plebani et al. 2025 review (PMID 40266896) addresses new insights in pre-analytical quality including AI-driven error detection

Staining & Processing Automation

• Rapid tissue processing (1-3 hour protocols) replacing overnight formalin fixation/paraffin embedding (FFPE)
• Intraoperative rapid staining with DESI-MS (desorption electrospray ionization mass spectrometry) providing real-time surgical margin assessment
• Automated multiplex IHC platforms (BOND RX, Leica, Ventana) with integrated image analysis

Flow Cytometry & Hematology

• High-parameter flow cytometry (20-50 color panels) now standard in academic hematopathology
• Mass cytometry (CyTOF) provides 40+ parameter immunophenotyping without spectral overlap
• Digital morphology systems (CellaVision, CellDyn) with AI-assisted differential and flag review
• Automated bone marrow aspirate analysis emerging

Molecular Diagnostics Platforms

• Droplet digital PCR (ddPCR): absolute quantification without calibration curves - MRD, ctDNA
• Oxford Nanopore sequencing: long-read, rapid, portable - intraoperative methylation and fusion detection
• PacBio HiFi: highly accurate long-read sequencing for structural variant and repeat expansion detection
• CRISPR-based diagnostics (SHERLOCK, DETECTR): isothermal amplification with attomolar sensitivity
• Single-molecule sequencing: emerging for direct RNA sequencing without reverse transcription

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8. Cytopathology Advances

Technology Integration

• ThinPrep and SurePath platforms now paired with automated AI screening (Hologic Genius, BD FocalPoint) - FDA cleared for cervical cytology co-testing
• Digital cytopathology: whole slide imaging increasingly applied to cytology specimens (fine needle aspiration, effusions, urine)
• Flow cytometry integration with FNA specimens for simultaneous morphologic and immunophenotypic analysis
• Rapid on-site evaluation (ROSE) augmented by AI for adequacy assessment

Molecular Cytopathology

• EUS-FNA samples now routinely triaged to molecular testing (NGS panels for pancreatic lesions, thyroid FNA molecular testing via Veracyte Afirma, ThyroSeq)
• Afirma Genomic Sequencing Classifier (GSC): reduces diagnostic thyroidectomies in indeterminate cytology
• ThyroSeq v3: mutation/fusion panel with >90% negative predictive value for benign disease
• FISH and RNA-based fusion panels applied to cytology cell blocks

Urine Cytology

• Paris System for Reporting Urinary Cytology (PSRUC) now widely adopted - standardized high-grade urothelial carcinoma reporting
• AI-assisted urine cytology screening reducing equivocal categories

Effusion Cytology

• Mesothelioma diagnosis: MTAP IHC loss (surrogate for CDKN2A deletion) on cytology specimens - reduces need for biopsy
• Malignant effusion profiling by ctDNA/cell-free DNA in pleural/peritoneal fluid increasingly validated

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9. Emerging & Frontier Technologies

Spatial Biology

• Spatial transcriptomics (Visium, Xenium, MERSCOPE, CosMx): maps gene expression with tissue morphology preserved - identifies tumor microenvironment heterogeneity, immune cell neighborhoods, and therapy resistance niches
• Simultaneous spatial epigenome + transcriptome profiling now feasible (Li et al. Nat Protoc 2025)

Single-Cell Pathology

• Single-cell RNA sequencing deconvolutes bulk tumor heterogeneity
• Direct application to pathology: defines cell-of-origin of poorly differentiated tumors, resolves lineage ambiguity in biphenotypic leukemia

Proteomics in Diagnostics

• Clinical mass spectrometry for protein biomarkers (MALDI-TOF for microorganism ID already standard)
• Plasma proteomics for early cancer detection (SomaScan, Olink proximity extension assay)

Artificial Intelligence - Next Steps

• Multimodal AI: integrating H&E + molecular + clinical data into unified diagnostic/prognostic models
• Federated learning: training AI on distributed hospital datasets without data leaving institutional firewalls
• Regulatory pathways: FDA Breakthrough Device Designation granted to several digital pathology AI tools (2024-2025)

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Summary Table: Key 2024-2026 Advances by Domain

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• Marra et al., Ann Oncol 2025 (PMID 40307127) - AI in pathology/oncology systematic review
• Zhang et al., Lab Invest 2024 (PMID 39053633) - digital pathology implementation
• Brodsky et al., Arch Pathol Lab Med 2025 (PMID 39836377) - generative AI in anatomic pathology
• Quinn et al., Histopathology 2026 (PMID 42011085) - WHO Breast 6th Edition
• Al Sharie et al., Front Oncol 2025 (PMID 41487568) - DNA methylation in neuropathology
• What's new in hematopathology 2025, J Pathol Transl Med - myeloid neoplasms WHO5/ICC
• Ferry et al., J Hematol Oncol 2024 (PMID 38978094) - mature lymphoid/plasma cell neoplasms classification