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Needle aspiration: Type of needle biopsy. Removal of fluid from a cyst or of cells from a tumor. A needle is used to reach the cyst or tumor, and to draw up (aspirate) samples for examination under a microscope. If the needle is thin, the procedure is called a fine needle aspiration or FNA. (See: Biopsy.)

Needle biopsy: Removal of fluid, cells, or tissue with a needle for examination under a microscope. There are two types: fine needle aspiration (FNA) and core biopsy. FNA uses a thin needle to draw up (aspirate) fluid or small tissue fragments from a cyst or tumor. A core needle biopsy uses a thicker needle to remove a cylindrical sample of tissue from a tumor.

Needle localization: Rrocedure used to guide a surgical breast biopsy when the lump is hard to locate or when there are areas that look suspicious on x-rays but where there is no distinct lump. A thin needle is inserted into the breast. X-rays are taken and used to guide the needle to the suspicious area. The surgeon then uses the path of the needle as a guide to locate the abnormal area to be removed.

Neoblastic: New tissue growth.

Neonatologist: Doctor specializing in the care of newborn (until about 6 weeks of age).

Neoplasm: Abnormal growth (tumor) starting from a single altered cell; neoplasm can be benign or malignant. Cancer, therefore, is a "malignant neoplasm".  A benign neoplasm is not cancerous.

Nephrologist: Doctor specializing in kidney diseases.

Nervous System: System of delicate nerve cells complexly interlaced with each other.  Primary elements include the brain, spinal cord, spinal nerves, autonomic ganglia, ganglionated trunks, and nerves that, together, maintain the vital function of reception and response to various internal and external stimuli.

Neurosurgeon: Doctor specializing in operations to treat nervous system disorders.

Neuroglia (also called "neuroglial" or simply "glia"): Cells and fibers that make up the tissues forming the interstitial (supporting) elements of the nervous system. Plays important role in the reaction of the nervous system to injury or infection.

Neutrophils: White blood cells that fight bacterial infection.

Nitrogenous base: A nitrogen-containing molecule having the chemical properties of a base.
Nodal status: Indicates whether cancer has spread (node-positive) or has not spread (node-negative) to lymph nodes.

Nodule: Small, solid lump locatable by touch.

Non-Hodgkin's lymphoma: Cancer of the lymphatic system, which is a network of thin vessels and nodes throughout the body designed to help it fight infection. What distinguishes non-Hodgkin's lymphoma from Hodgkin's lymphoma is the absence of a type of cell called the Reed-Sternberg cell. This cell is present only in Hodgkin's lymphoma. Treatment methods for Hodgkin's and non-Hodgkin's lymphomas are very different.

Nuclear medicine scan: Method of localizing diseases of internal organs such as the brain, liver, or bone. Small amounts of a radioactive isotope are injected into the blood. It collects in certain organs and a special camera called scintillation camera is used to produce an image of the organ and detect areas of disease.

Nucleic acid: A large molecule composed of nucleotide subunits.

Nucleotide: A subunit of DNA or RNA consisting of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or 
RNA molecule. See DNA, base pair, RNA.

Nucleus : Center of a cell where DNA is found. Studying the size and shape of a cell's nucleus under a microscope helps pathologists tell cancerous cells from benign cells. The cellular organelle in eukaryotes that contains the genetic material.

Nurse practitioner : Registered nurse with a master's or doctoral degree. Licensed nurse practitioners actually diagnose and manage illness and disease, usually working closely with a doctor. In many states, they may prescribe medications.