histopathology

Histopathology is the branch of pathology that focuses on disease of tissues as revealed by microscopic examination. It uses tissue samples obtained by biopsy, surgical resection, or autopsy to study cellular architecture and tissue organization in order to diagnose disease and understand its mechanisms.

The typical workflow starts with specimen handling, fixation in formalin, processing and embedding in paraffin, and cutting thin sections that are stained for visualization. Hematoxylin and eosin is the routine stain. Special stains, immunohistochemistry, in situ hybridization, and, in selected cases, electron microscopy provide additional information.

Histopathologic interpretation by a pathologist establishes diagnoses, often with judgments about cancer grade, depth of invasion, and margins, and may contribute to staging and prognosis. Findings influence treatment decisions across oncology, inflammatory and infectious diseases, and metabolic disorders. Cytology examines individual cells and is closely related to histopathology, often used for less invasive sampling such as fine-needle aspirates.

Subspecialties include surgical pathology and cytopathology, with intraoperative frozen-section consultation. Autopsy pathology examines deceased individuals. Advances in digital pathology and whole-slide imaging enable remote review and computer-assisted analysis. Molecular pathology and ancillary tests integrate genomic and proteomic data to refine diagnoses and guide targeted therapies. Limitations include sampling error and interpretive variability, underscoring the need for standardized quality control.