What is Pathology?


The term pathology can be translated into the study (logos) of suffering (pathos). It is a discipline that is devoted to studying both structural and functional changes while bridging clinical practice and basic science. Through morphologic, molecular, immunologic, and microbiologic techniques, pathology tries to explain why some signs and symptoms occur along with providing a basic understanding of rational therapy and clinical care. Traditionally, pathology can be divided into general and systemic (special) pathology). General pathology involves the basic reactions of cells and tissues to stimuli that lead to disease. Systemic pathology revolves around the specific responses of certain tissues to well-defined stimuli. The core of pathology can be formed by aspects of a disease. This includes:

  • Etiology – the cause of disease. Generally, it can be divided into intrinsic (genetic) or acquired. 

  • Pathogenesis – the mechanism of disease. It refers to the sequence of events caused by the etiologic agent or stimulus. Pathogenesis does not only involve the study of the etiology but also the various events that lead to the development and progression of the disease.

  • Morphologic changes – the structural alterations. These alterations seen in tissues or cells are characteristic or diagnostic. Diagnostic pathology helps identify the nature and progression of the disease through the study of changes and chemical alterations. 

  • Clinical significance – the functional consequences of the morphologic changes. This results in the signs and symptoms experienced in the disease. It also influences the course and prognosis of the illness. 

Surgical Pathology

Surgical pathology is one of the most time consuming and significant branch of pathology. It involves the examination of tissues to achieve a diagnosis. Specimens that are surgically removed such as core biopsies from suspected cancers, skin biopsies, and specimens resected in the operating room are subjected to examination or analysis. The molecular properties of these specimens are evaluated through immunohistochemistry and various other tests. Tissue sections are processed for histological examination using either frozen section or chemical fixation. A frozen section involves freezing of the tissue to generate thin slices of specimens that are mounted on glass slides. The slides are then stained with antibodies or chemicals before viewed under a microscope. The pathologist also performs autopsies to evaluate diseases, injuries, and determine the cause of death. 


Cytopathology is a branch studying and diagnosing diseases on the cellular level. It is often used to help in the diagnosis of cancer, infectious diseases, and inflammatory conditions. It can be performed on specimens that contain tissue fragments or free cells. These specimens can be collected through procedures such as fine needle aspiration, removed through abrasion, or spontaneous exfoliation. One good application of cytopathology is the screening tool (pap smear) used in the detection of precancerous cervical lesions. 

Molecular Pathology

This is a fairly recent branch of pathology that has made great progress in the past decade. It involves the diagnosis and study of diseases via molecular examination of tissues, organs, and bodily fluids. Diseases such as cancer have been found to be due to alterations or mutations of the genetic code. The identification of these changes helps clinicians to choose the best treatment for the individual. This has resulted in personalized medicine where molecular analysis is used to predict responses to different therapies based on each individual’s genetic component. Molecular pathology also includes studying the development of genetic and molecular approaches to both the diagnosis and classification of tumors. It has also allowed experts to design and authenticate biomarkers to assess the prognosis and likelihood of disease in individuals. Molecular assays have high levels of sensitivity allowing the detection of small tumors that are usually undetectable through other means. This will lead to earlier diagnosis, improved care, and better prognosis for patients. 

Laboratories and Staff

There are different pathology labs available. This includes:

  • Hospital labs – that support clinical services that are provided by the hospital. Most pathology labs at hospitals usually include cytopathology, surgical pathology, autopsy, and clinical pathology. 

  • Reference labs – are private and commercial labs that provide special laboratory testing. These tests are generally referred from hospitals and other patient care facilities. 

  • Public health labs – are managed by the local health departments or state to protect the general population from potential health threats. They perform tests to monitor diseases in the community. 

All laboratories require trained staff such as:

  • Pathologists – are physicians who specialize in the diagnosis of disease. They may be general pathologists or have a subspecialty such as hematopathology, cytopathology, nephropathology, dermatopathology, etcetera. They ensure accurate and timely reporting of tests while serving as a resource that aids in result interpretation.

  • Pathologists’ assistants – are individuals who assist with some responsibilities of the pathologist. This includes gross description and dissection. Pathologists’ assistants work closely with pathologists and can also assist in intraoperative assessment and tissue selection.

  • Cytotechnologists – are individuals who help in screening specimens composed of cells instead of whole sections. They screen specimens and refer abnormal cells to pathologists for further review. 

  • Histotechnologists – manage tissue processing in the lab. They also make slides (fixing, embedding, sectioning, staining) that will be evaluated by the pathologists. 

  • Medical laboratory technician – perform tests and analysis on specimens to determine the absence or presence of disease.

  • Phlebotomists – are individuals trained to draw blood from a patient for various purposes such as research, testing, donations, or transfusions. 


  1. Introduction to the pathology laboratory. Healio Learn Genomics. Accessed 3/8/2019. https://www.healio.com/hematology-oncology/learn-genomics/pathology-assessment-of-tumor-tissue/introduction-to-the-pathology-laboratory

  2. What is pathology? McGill Department of Pathology. Accessed 3/8/2019. https://www.mcgill.ca/pathology/about/definition

  3. Cellular Adaptations, cell injury, and cell death. Robbins and Cotran Pathologic Basis of Disease; page 6: 7th Edition, 2005.