Physicians, Pathologists

• Compound microscope + autopsy knife1858–1892

  Compound microscope + autopsy knife (Virchow-era cellular pathology)

  Rudolf Virchow's 1858 publication established that disease was a cellular phenomenon, transforming the microscope from a curiosity into the defining instrument of the profession. Pathologists in this era worked primarily with autopsy material: removing organs, examining tissue slices with simple compound microscopes, and correlating microscopic findings with disease manifestations. The standard tissue preparation was freehand sectioning with a blade; formal paraffin embedding and microtome sectioning came in the 1870s-1880s. The compound microscope and the autopsy knife remained the pathologist's only tools for this entire era.

• Paraffin embedding1892–1936

  Paraffin embedding, H&E staining, and the clinical laboratory (formalized tissue processing era)

  The arrival of paraffin embedding (1880s) and hematoxylin and eosin (H&E) staining as the standard histologic preparation transformed biopsy pathology from an occasional autopsy service into a routine clinical workflow. A surgeon could now submit a biopsy and receive a microscopic diagnosis within 24-48 hours. Clinical laboratories -- processing blood, urine, and cultures -- were staffed at US hospitals beginning in the 1890s, with pathologists serving as laboratory directors. By the 1920s, over 3,000 US hospitals reported incorporating clinical laboratories. This era established the workflow that would define pathology for the next century: submit specimen, process and section, stain, examine under the microscope, report.

  Effect on the work

  Full-time pathology positions appeared at academic medical centers from 1892 onward, displacing the prior model of part-time autopsy work by clinicians. By 1922, pathology had formalized enough as a profession that the ASCP was founded; by 1936, the ABPath provided formal board certification.

• Board certification1936–1970

  Board certification (ABPath 1936) and postwar laboratory expansion

  The founding of the American Board of Pathology in July 1936 in Chicago formalized the specialty and established credentialing standards for anatomic and clinical pathology certification. The postwar decades saw explosive growth in the clinical laboratory: new assays for chemistry, hematology, microbiology, and immunology multiplied the diagnostic tests a pathology department could offer. Automated cell counting and the first clinical chemistry analyzers appeared in the 1950s-1960s (the Technicon AutoAnalyzer, introduced 1957, was the first automated clinical chemistry platform). The pathologist's role expanded from tissue diagnosis to laboratory medicine director, overseeing a widening array of clinical laboratory operations.

  Effect on the work

  Training program enrollment rose dramatically: from approximately 10 programs in 1926 to approximately 700 by 1963. The pathologist workforce grew from an estimated 1,500 in 1936 to approximately 8,000 by 1960, driven by hospital expansion and clinical laboratory growth in the postwar period.

• Automated hematology analyzers1970–1996

  Automated hematology analyzers, flow cytometry, and immunohistochemistry (IHC)

  The 1970s-1990s brought a wave of automation to the clinical laboratory and a new toolkit for histopathologic interpretation. Automated hematology analyzers (Coulter STKS, Sysmex) replaced manual differential counts for most routine specimens; flow cytometry (commercialized in the 1970s) enabled quantitative immunophenotyping of leukemias and lymphomas. Immunohistochemistry, routinely available from the mid-1970s onward, transformed surgical pathology: pathologists could now apply antibody panels to tissue sections to determine cell lineage, receptor expression, and molecular markers, converting histologic pattern recognition from a largely morphologic art into a marker-guided science. These tools dramatically expanded what a pathologist could determine from tissue and drove a parallel expansion in subspecialization: dermpath, hemepath, neuropath, and cytopathology became increasingly distinct practices within the profession.

• Liquid-based cytology1996–2015

  Liquid-based cytology, molecular diagnostics, and NGS (ThinPrep 1996, PCR-based assays, FISH)

  The FDA approval of the ThinPrep liquid-based cytology system on May 20, 1996, modernized the Pap test -- reducing false negatives, enabling reflex HPV testing from the same sample, and introducing a form of automation to the highest-volume cytology workflow. The same era brought PCR-based molecular diagnostics into routine clinical pathology: FISH for HER2 amplification in breast cancer (1990s), BCR-ABL testing for CML, HPV genotyping. Next-generation sequencing arrived in pathology laboratories in the late 2000s and early 2010s: Foundation Medicine launched FoundationOne CDx in 2012, the first comprehensive genomic profiling test for solid tumors. These tools transformed the pathologist's report from a morphologic description ("invasive ductal carcinoma, grade II") into a molecularly annotated profile that directly guides targeted therapy selection.

  Effect on the work

  Molecular pathology became the fastest-growing subspecialty within pathology during this era. The expanded diagnostic scope required new training: pathology residencies added molecular and genomic pathology rotations, and new subspecialty certifications (molecular genetic pathology, via ABMGG/CAP joint program) emerged.

• Whole-slide imaging1999–2021

  Whole-slide imaging and digital pathology (Aperio 1999, telepathology, remote sign-out)

  Aperio Technologies, founded in 1999 in Vista, California, pioneered the commercial whole-slide imaging (WSI) scanner that could digitize an entire glass microscopy slide into a high-resolution digital file navigable on a computer screen. By the time Leica Biosystems acquired Aperio in 2012 for an undisclosed sum, Aperio had 1,100 systems deployed worldwide. WSI enabled a capability that had not been possible with glass slides: remote sign-out. A pathologist at one institution could review slides from another without physical transport; subspecialty consultations that once required shipping glass became same-day digital transfers. The COVID-19 pandemic accelerated digital pathology adoption sharply as laboratories shifted to remote work. By 2020-21, multiple FDA-cleared digital pathology platforms (PathAI AISight, Proscia Concentriq, Indica Labs HALO AP) provided regulatory approval for primary diagnosis rather than just consultation.

  Effect on the work

  Digital pathology expanded the geographic reach of pathologist expertise: a dermatopathologist in Boston could read slides from a community hospital in rural Montana. It also created the computational substrate on which AI would run -- every digital slide became a potential input for machine learning algorithms.

• FDA-authorized AI for digital pathology2021–present

  FDA-authorized AI for digital pathology (Paige 2021, Ibex 2025, PathAI, Proscia, Indica)

  On September 22, 2021, the FDA authorized Paige Prostate Detect as the first AI software in pathology cleared for primary diagnosis -- a de novo authorization for an algorithm that analyzes prostate biopsy whole-slide images and generates case-level and slide-level cancer detection alerts. This was the pivotal regulatory moment for AI in pathology: it established that an AI algorithm could serve as a decision-support tool in primary diagnosis (not just research), and it set the template for subsequent clearances. By 2025, a full suite of FDA-cleared AI pathology tools was in routine clinical use: Paige Breast Suite, Ibex Prostate Detect (510(k) January 2025), PathAI AISight Dx (primary diagnosis IMS), Proscia Concentriq AP-Dx (32,000 patients diagnosed daily as of July 2025), and Indica Labs HALO AP Dx. Every cleared tool is explicitly assistive-only; pathologist sign-out is required for all. The AI era in pathology is not autonomous diagnosis -- it is augmented diagnosis, where AI catches errors the human eye misses and compresses the time required to process routine cases, freeing pathologist attention for the complex interpretive work that AI cannot do.

  Effect on the work

  AI reduces prostate biopsy slide review time by 21.9% per slide and diagnostic errors by 70% (Paige Prostate Detect, Archives of Pathology 2025 pivotal study). Paige Breast Lymph Node achieves 98% sensitivity for metastases with 55% reading time reduction. These efficiency gains matter: US pathologist cancer caseload per pathologist rose 41.7% from 2007 to 2017 as workforce shrank against rising cancer incidence; AI is a direct response to this workload pressure.

What's changing in your day

Three parts of your work where AI is already doing real lifting, and what stays yours.