Glossary of medical terms and definitions

Medical terminology and definitions associated with cancer can be difficult to understand. We’ve explained some of them to help make things clearer.

Common medical terms

Terms Definition
Adjuvant therapy Adjuvant therapy is used after initial treatment for cancer such as surgery. It reduces the chance of the cancer coming back. Adjuvant therapies include chemotherapy, radiotherapy, immunotherapy and hormone therapy.
Benign Benign refers to a condition, tumour or growth which is not cancerous. It does not spread to other parts of the body. A benign tumour usually grows slowly and is not harmful. However, it can cause problems if it becomes too big or is near blood vessels, the brain, nerves or organs.
Cancer of unknown primary If it’s not clear where a cancer has started but it has spread to another part of the body, it’s called a cancer of unknown primary (CUP). A secondary cancer has been found but the site of the primary tumour is unknown.

The grade indicates how fast the cancer is growing. This is judged by what it looks like under a microscope and how different it looks from a normal cell. The most common grading system is:

  • Grade 1 – the cancer cells look like normal cells and aren’t growing quickly
  • Grade 2 – the cancer cells don’t look like normal cells and are growing faster than normal cells
  • Grade 3 – the cancer cells look abnormal and grow quickly, potentially spreading to other tissues more easily
Malignant is another word for cancerous and means cancer cells which can invade and kill nearby tissue and spread to other parts of the body.
Metastatic cancer Metastatic cancer is a cancer which has spread from the part of the body where it originated to other parts of the body. It’s also called secondary cancer.
Neoadjuvant therapy Neoadjuvant therapy is given before the main treatment, which is usually surgery. It aims to decrease the chance of the cancer coming back and to shrink the cancer so it’s easier to remove. Neoadjuvant therapies include chemotherapy, radiotherapy and hormone therapy.
Palliative care Palliative care aims to improve quality of life through treatment, care and support for people living with a life-limiting illness. It’s also called supportive care. It can involve managing physical symptoms including pain and psychological, social and spiritual support for family and carers as well as the patient.
Primary cancer Primary cancer means where the cancer started. Cancers are named based on the primary site. For example, cancer which starts in the liver is called primary liver cancer.
Prognosis Prognosis means the likely outcome of cancer or the chance of recovery or recurrence.

A recurrence is when the cancer returns after treatment. It can come back weeks, month or years after the original cancer was treated. The chance of recurrence depends on the type of primary cancer.

Remission Remission means that the signs and symptoms of cancer have partially or completely disappeared. Complete remission is when treatment has got rid of all the cancer cells. Partial remission is when the cancer has partially responded to treatment but part of the tumour or some cancer cells remain.
Secondary cancer

Secondary cancer describes a cancer which has spread from where it started. For example, if breast cancer spreads to the lungs, it’s known as secondary breast cancer. Some of the most common places for secondary cancers to grow are bones, lungs, liver and lymph nodes. Where a cancer is most likely to spread depends on where the primary cancer was. Secondary cancer is also called metastatic cancer.


The stage of a cancer means the size of the tumour and how far it has spread. There are different types of staging systems for different types of cancer. One of the most common methods of staging is:

  • Stage 0 – the cancer is where it started and hasn’t spread
  • Stage I – the cancer is small and hasn’t spread
  • Stage II – the cancer has grown, but hasn’t spread
  • Stage III – the cancer is larger and may have spread to the surrounding tissues and/or lymph nodes
  • Stage IV – the cancer has spread to at least one other body organ. This is called ‘secondary’ or ‘metastatic cancer’
Systemic therapy Systemic therapy involves drugs which spread throughout the body to treat cancer cells. It includes chemotherapy, biological therapy and hormone therapy.

Radiotherapy terminology

Terms Definition
Brachytherapy Brachytherapy is a type of internal radiotherapy treatment that delivers radiation to cancer cells using sealed sources called implants. The implants are placed close to the tumour site and release radiation into the cancer cells, destroying them, while the surround healthy tissue receives a lot less.
Chemoradiation A combined approach to cancer treatment that uses both chemotherapy and radiotherapy
Deep inspiration breath hold (DIBH) DIBH is a simple yet highly effective technique that uses surface-guided radiotherapy (SGRT) and breath holding to reduce damage to healthy tissues while receiving radiotherapy for cancers of the breast or near the chest wall. When taking a deep breath, your lungs inflate and push some of your vital organs (including the heart) away from the chest wall and the area being treated. DIBH minimises the amount of radiation to your heart, lungs or liver, meaning you get fewer or less severe side effects.
External beam radiotherapy (EBRT) EBRT refers to the delivery of targeted radiation beams from outside the body. EBRT is delivered from a machine known as a linac, over the course of several daily treatment sessions, called fractions. Depending on your condition, your treatment course for EBRT may last anywhere between a few days to a number of weeks.
Image-guided radiotherapy (IGRT) IGRT uses computer imaging techniques to ensure you’re in the correct position while receiving radiotherapy. Before your radiotherapy starts, you’ll have a scan of your tumour which will then be compared to a previous scan from your planning appointment. Your radiologist will use these to precisely align you so that the radiation beams will be targeted accurately at the tumour site.
Intensity-modulated radiotherapy (IMRT) IMRT is a type of radiotherapy that uses computer-generated images to show the size and shape of the tumour. During treatment, beams of radiation are delivered together at different intensities and from a number of angels, to create a shape that closely fits the area of the tumour.
MR linac An MR linac is an advanced radiotherapy technology that combines magnetic resonance imaging (MRI) scanning with radiotherapy. This allows us to adapt radiotherapy delivery during your treatment session so we can treat tumours more accurately. At GenesisCare, we have an advanced MR linac called the MRIdian in our London and Oxford centres.
Radiotherapy Radiotherapy is a treatment that uses high-energy rays, such as X-ray, to destroy cancer cells. Radiotherapy kills cancer cells by damaging their DNA. The radiation can also damage the DNA of some healthy cells and this causes side effects. Radiotherapy treatment is usually external and the radiation is delivered from a machine outside of the body, but for some cancers you may receive internal radiotherapy where radiation is released from within the body, for example, during surgery or using specialised equipment or targeted radioactive medicines (Theranostics).
Stereotactic ablative radiotherapy (SABR) SABR targets tumours in the body with higher doses of radiation than conventional radiotherapy, and usually with a few days. With a higher dose of radiation, you have a better chance of destroying the tumour. This treatment is carefully planned and precisely delivered to limit damage to surrounding healthy tissues and reduce side effects.
Stereotactic radiosurgery (SRS) SRS is an advanced radiotherapy technique that precisely delivers multiple beams of radiation to tumours in the brain and spinal cord. SRS can be delivered in a single treatment session, sometimes in as little as 20 minutes, and is recognised for its ability to preserve quality of life for people with cancers that have spread to the brain.
Rectal spacers

Rectal spacers, or spacers, are an effective technique that help reduce the side effects of prostate cancer radiotherapy, by moving the rectum away from the prostate gland during treatment. The absorbable spacer is injected during one-off procedure and is gradually eliminated naturally from the body.

Surface-guided radiotherapy (SGRT) SGRT uses sophisticated 3D and 4D camera technologies to confirm you’re set up in the correct position for radiotherapy. During treatment, the cameras monitor your movement to ensure accurate targeting. Unlike conventional radiotherapy, SGRT means you don’t have to have any permanent markings on your skin, so is often referred to as tattoo-free treatment.
Volumetric modulated arc therapy (VMAT)

VMAT is an advanced radiotherapy treatment that delivers radiation to cancer cells as the machine (called a linac) moves in an arc around you. During VMAT, the linac also automatically changes the shape and intensity of the radiation beam, maximising the radiation to the tumour while limiting delivery to the surrounding healthy tissue. At GenesisCare, we use VMAT radiotherapy as standard for a wide range of cancer types in our centres.

What is cancer?

Cancer is where cells in a part of the body grow and reproduce uncontrollably. These cancerous cells can spread and destroy surrounding healthy tissue, including organs. Cancer can start almost anywhere in the body.

Normal cells grow and divide in an orderly way. When they are worn out or damaged, they die and new cells take their place. In cancer the cells keep growing and making new cells which are not needed. These extra cells may form growths or tumours.

A solid tumour is a mass of tissue which is found in many cancers. Cancers of the blood don’t form solid tumours. Tumours can be benign or malignant. Benign tumours grow slowly and aren’t harmful. Malignant tumours are cancerous and can spread to other parts of the body.

Terms Definition
Breast cancer

Breast cancer starts in the breast tissue when cells in the breast divide and grow in an uncontrolled way. It can begin in different parts of the breast. Most breast cancers start in the ducts, which are tubes that carry milk to the nipple. Cancer can also start in the lobules, which are the glands that produce milk. It’s more uncommon for cancer to begin in the fibrous and fatty connective tissue in the breast.

Breast cancer can be non-invasive or invasive:

  • Non-invasive breast cancer means there are cancer cells in the breast, but they’re only found inside the milk ducts and have not spread any further. This is also called ductal carcinoma in situ (DCIS). Sometimes the cancer cells stay inside the ducts, but they may also grow into the surrounding breast at a future time
Prostate cancer

Prostate cancer develops when cells in the prostate gland grow in an uncontrolled way. Some prostate cancer grows so slowly it doesn’t cause any problems. Therefore, many men with prostate cancer may never need treatment. If the prostate cancer grows quickly and is likely to spread, it needs to be treated.

There are different types of prostate cancer:

  • Early prostate cancer (also called localised prostate cancer) is when the cancer cells are contained inside the prostate and haven’t spread. This type of cancer may not need treatment
  • Locally advanced prostate cancer means the cancer has grown through the capsule which surrounds the prostate and may have spread into nearby tissue or organs
  • Advanced prostate cancer is when the cancer cells have spread from the prostate to other parts of the body. It most commonly spreads to the bones and lymph nodes. Advanced prostate cancer can’t be cured, but treatment can keep it under control
Skin cancer

Skin cancer is the growth of abnormal cells in the outermost layer of the skin called the epidermis. It’s a common form of cancer which often develops on skin which is exposed to the sun. It can also develop on skin not usually exposed to sunlight.

There are three main types of skin cancer:

  • Basal cell carcinoma starts in the basal cells at the bottom of the epidermis. It’s very common and appears most often on skin exposed to the sun, such as the head and neck. Most basal cell carcinomas grow slowly and rarely spread to other parts of the body
  • Squamous cell carcinoma is the second most common type of skin cancer. It develops in the squamous cells, which make up the middle and outer layers of the skin. It grows slowly and doesn’t spread unless left untreated for a long time
  • Melanoma develops in cells called melanocytes. These cells produce melanin which helps protect the skin from the sun’s ultraviolet light. Melanoma is a serious form of skin cancer and can spread to other organs if not treated at an early stage
Blood cancer

Most blood cancers develop in bone marrow where blood is produced, and there’s uncontrolled growth of abnormal blood cells. These cancerous cells stop the blood performing many of its functions.

The most common types of blood cancer are:

  • Leukaemia is caused by an increase in the number of abnormal white blood cells. These cells aren’t able to fight infection and crowd out the red blood cells and platelets which the body needs to be healthy
  • Lymphoma starts in the lymph glands or other organs of the lymphatic system, which helps protect the body from infection. There are many different types of lymphoma
  • Myeloma, which is also called multiple myeloma, develops from plasma cells. It affects numerous places in the body and can cause bone pain and bone thinning