What Is a Biopsy?

A biopsy is a medical procedure in which cells, tissue, or fluid are removed from a living patient for examination by a pathologist, with the goal of diagnosing disease, assessing its extent, or guiding treatment decisions. The term derives from the Greek roots for life and appearance, reflecting the procedure's purpose of examining living tissue. Biopsies are the diagnostic gold standard for cancer, where visual and imaging findings are insufficient to confirm malignancy or determine tumor type without direct tissue analysis.

The procedure spans a wide range of clinical specialties, including oncology, gastroenterology, nephrology, dermatology, and pulmonology. Advances in imaging technology, minimally invasive instrumentation, and molecular diagnostics have considerably expanded what can be learned from a biopsy sample, enabling histological diagnosis and genetic profiling of the tissue to guide targeted therapy selection.

Types of Biopsy Procedures

Biopsy methods are selected based on the anatomical location, size, and accessibility of the target tissue. Needle biopsy encompasses several subtypes: fine-needle aspiration (FNA) withdraws cells and fluid using a thin needle, while core needle biopsy uses a hollow needle with a cutting tip to extract a cylindrical core of tissue that preserves histological architecture. Image-guided needle biopsy combines ultrasound, CT, or MRI guidance with core needle technique to reach lesions in the liver, lung, kidney, or prostate that are not palpable from the skin surface. Endoscopic biopsy passes forceps through a flexible endoscope to take mucosal specimens from the gastrointestinal or respiratory tract. Surgical biopsy, either incisional (removing a portion) or excisional (removing the entire lesion), is reserved for cases where other methods yield insufficient tissue or inconclusive results. The American Cancer Society's overview of biopsy types provides a structured comparison of these approaches in the context of cancer diagnosis.

Histopathological Analysis

Once collected, biopsy specimens undergo processing in a pathology laboratory. Tissue is fixed in formalin to halt cellular degradation, embedded in paraffin wax, sectioned at three to five micrometer thickness, and stained with hematoxylin and eosin (H&E) to reveal cell morphology. Pathologists examine the sections under a light microscope to assess nuclear size and shape, mitotic activity, tissue architecture, and invasion of surrounding structures. Immunohistochemistry (IHC) applies antibodies conjugated to detectable labels to identify specific proteins expressed by cells, enabling tumor subtyping. For example, breast cancer specimens are routinely tested for estrogen receptor (ER), progesterone receptor (PR), and HER2 expression, because the results determine whether hormonal therapy or HER2-targeted agents are appropriate. The NCI cancer dictionary definition of biopsy situates the procedure within the broader framework of cancer staging and treatment planning.

Emerging Techniques

Liquid biopsy is an approach that detects tumor-derived components, including circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), and exosomes, in a blood sample rather than from a tissue specimen. This enables repeated sampling over the course of treatment without the invasiveness of repeat tissue procedures, facilitating real-time monitoring of tumor evolution and treatment response. Advances in massively parallel sequencing have made liquid biopsy panels increasingly sensitive, though clinical validation for most tumor types is ongoing. Another development is optical biopsy, in which spectroscopic or optical coherence tomography methods characterize tissue in situ during endoscopy, providing immediate feedback without the delay of laboratory processing. Johns Hopkins Medicine's clinical overview of biopsies describes how emerging technologies are being integrated with traditional biopsy approaches in academic medical centers.

Applications

Biopsy has applications in a range of fields, including:

• Oncology: cancer diagnosis, grading, and molecular profiling for therapy selection
• Transplant medicine: monitoring organ rejection through protocol surveillance biopsies
• Infectious disease: diagnosis of tuberculosis, fungal infections, and viral hepatitis in tissue
• Dermatology: identification of melanoma, basal cell carcinoma, and inflammatory skin diseases
• Nephrology: assessment of glomerular disease and chronic kidney injury patterns