Copy number variation is a change in how many copies of a DNA segment a person’s cells contain. It can involve extra copies (gains) or missing copies (losses) of genes or larger chromosome regions. In oncology, it is commonly used to help describe tumor biology and guide diagnostic classification. It is also used in genetics to evaluate inherited (germline) conditions.

Gene fusion is a genetic change where parts of two different genes become joined together. This joining can create a new “fusion” gene that may change how a cell behaves. Gene fusion is commonly discussed in cancer care because some fusions help drive tumor growth. It is also used in oncology testing to support diagnosis and guide treatment selection.

An Actionable mutation is a change in a tumor’s DNA (or related biomarker change) that can help guide clinical care. It is “actionable” because it may be linked to a specific therapy, a clinical trial option, or a recommended testing or monitoring approach. The term is most commonly used in oncology pathology reports and precision medicine discussions. It can apply to solid tumors and some blood cancers, depending on the disease and setting.

A Driver mutation is a genetic change in a cancer cell that helps the cancer start or grow. It is different from many other mutations that are present but do not affect tumor behavior. The term is commonly used in oncology reports, tumor genomic testing, and treatment planning. It is also used in research to understand why certain cancers respond to specific therapies.

A Tumor suppressor gene is a gene that helps keep cells from growing and dividing out of control. It acts like a cellular “brake,” supporting normal DNA repair, cell-cycle checkpoints, and cell death when damage is severe. When a Tumor suppressor gene is altered (mutated) or inactivated, cancer risk can increase because growth control is weakened. The term is commonly used in cancer genetics, tumor molecular testing, pathology reports, and oncology treatment planning discussions.

An Oncogene is a gene that can drive cancer when it becomes abnormally active. It is often a changed version of a normal gene involved in cell growth and survival. In oncology, Oncogene changes are discussed in tumor biology, genetic testing, and targeted therapy. Clinicians use this concept to help explain why a cancer grows and how it may respond to treatment.

A Tumor marker is a measurable substance or feature linked to cancer. It can be found in blood, urine, body fluids, or tumor tissue. Clinicians use it alongside symptoms, imaging, and biopsy results. It most often helps with monitoring and treatment planning rather than stand-alone diagnosis.

CTC most commonly refers to **circulating tumor cells**. These are **cancer cells that have detached from a tumor and entered the bloodstream**. CTC testing is usually done from a **blood sample** and is often discussed as part of “liquid biopsy” approaches. It is used mainly in oncology to **help assess prognosis, monitor disease over time, and support research**.

Circulating tumor cells are cancer cells that have entered the bloodstream from a tumor site. They can sometimes be detected with a blood sample using specialized laboratory methods. They are studied to better understand how cancer spreads and how it responds to treatment. They are most commonly discussed in the context of “liquid biopsy” in solid-tumor oncology.

cfDNA stands for cell-free DNA, which is small DNA fragments found circulating in the bloodstream. It comes from normal cells and, in some people with cancer, from tumor cells as well. Clinicians most often measure cfDNA through a blood sample as part of a “liquid biopsy” approach. It is commonly used in oncology to support tumor profiling and disease monitoring in selected situations.