Pathology is a branch of medical science that involves the study and diagnosis of disease through the examination of surgically removed organs, tissues (biopsy samples), bodily fluids, and in some cases the whole body (autopsy). Aspects of a bodily specimen that may be considered include its gross anatomical make up, appearance of the cells using immunological markers and chemical signatures in the cells. Pathology also includes the related scientific study of disease processes whereby the causes, mechanisms and extent of disease are examined. Areas of study include cellular adaptation to injury, necrosis (death of living cells or tissues), inflammation, wound healing, and neoplasia (abnormal new growth of cells). Pathologists specialize in a wide range of diseases including cancer and the vast majority of cancer diagnoses are made by pathologists. The cellular pattern of tissue samples are observed under a microscope to help determine if a sample is cancerous or non-cancerous (benign). Pathologists also employ genetic studies and gene markers in the assessment of various diseases.
Surgical Pathology is the most significant and time consuming branch of pathology with a primary focus on examining tissues with the naked eye or under a microscope for definitive diagnosis of disease. Surgically removed specimens are received from sources such as small biopsies of skin, core biopsies for the diagnosis of cancer, and the operating room where tumours are removed. Surgical pathology involves macroscopic (gross) and microscopic (histologic) tissue analysis where the molecular properties of tissue samples are assessed by immunohistochemistry or other laboratory tests.
Histological sections of tissue are processed for microscopic viewing using either chemical fixation or frozen section. Frozen section processing involves freezing the tissue and generating thin frozen slices of the specimen which are mounted onto glass slides. Prior to viewing the tissue under a microscope, slides processed by chemical fixation or frozen section are either stained with chemicals or antibodies to reveal cellular components.
Cytopathology is a branch of pathology that studies and diagnoses diseases on the cellular level. It is usually used to aid in the diagnosis of cancer, but also helps in the diagnosis of certain infectious diseases and other inflammatory conditions. Cytopathology is generally used on samples of free cells or tissue fragments that spontaneously exfoliate or are removed from tissues by abrasion or fine needle aspiration, in contrast to histopathology, which studies whole tissues.
Molecular Pathology is a relatively recent discipline that has achieved remarkable progress over the past decade. It emphasizes the study and diagnosis of disease through the examination of molecules within organs, tissues or bodily fluids. Many diseases such as cancer are caused by mutations or alterations in the genetic code of a person, and identification of specific hallmark mutations allows clinicians to classify a disease and choose the appropriate treatment. As a result, molecular analysis is leading the way towards personalized medicine by allowing us to predict a patient’s response to certain anti-cancer therapy based on their own genetic make-up. Molecular Pathology includes the development of molecular and genetic approaches to the diagnosis and classification of human tumours and also to design and validate predictive biomarkers for prognosis of the disease, and susceptibility of developing certain cancers in individuals. The high levels of sensitivity provided by molecular assays allows for the detection of very small tumours that are otherwise undetectable by other means, and will likely result in earlier diagnosis, improved patient care and better outcomes for survival.