What is large granular lymphocytic leukaemia (LGLL)?

Around 200 people in the UK are diagnosed with LGLL each year.

LGLL happens when the body makes too many abnormal large granular lymphocytes in the bone marrow and not enough of the other types of blood cells. There are three main types of lymphocytes: B cells, T cells and NK cells. LGLL affects the T cells or, less commonly, the NK cells.

There are two main types of LGLL:

  • slow growing (chronic) T-cell or NK-cell LGLL (this is the most common type)
  • fast growing (aggressive) T-cell and/or NK-cell LGLL (a rare type).

> Download our fact sheet on LGLL to find out more

What causes LGLL?

We don’t know exactly what causes LGLL, but we do know that there are some things that can affect how likely you are to develop it:

  • Sex – LGLL affects both men and women, but it’s slightly more common in women.
  • Age – LGLL mainly affects older people – the average age at diagnosis is 60. Children rarely get LGLL.
  • Abnormal cell pathways and gene mutations – people with LGLL may have abnormalities in genes such as STAT3 and/or STAT5.
  • Other health conditions – around 30% of people with LGLL have rheumatoid arthritis. Rheumatoid arthritis is the second mostcommon form of arthritis in the UK and causes inflammation in the joints. This suggests that overactivity of the immune system may be one of the causes of LGLL.



Everyone is different, so it’s important to remember that not everyone will have the same symptoms. Around two thirds of people with LGLL have symptoms when they’re diagnosed. Common symptoms before diagnosis include:

  • extreme tiredness (fatigue) which may be caused by a lack of red blood cells (anaemia)
  • muscle, bone and joint pain
  • infections
  • chronic neutropenia (a low level of a certain type of blood cell called neutrophils which means that you’re more at risk of infection)
  • swelling of the lungs (pneumonia)
  • an enlarged spleen
  • sore throat and loss of voice
  • night sweats and difficulty sleeping
  • breathlessness
  • a loss of appetite.


Tests and diagnosis

LGLL is most often diagnosed from a full blood count (FBC) which is a blood test that measures the number of each type of cell in your blood: red cells, white cells and platelets. A FBC will give an initial diagnosis of LGLL, because the doctor can see the large pink granules under a microscope. The blood count has to be repeated after a few weeks to confirm the diagnosis.

As LGLL is difficult to diagnose, your doctors may have to do some more tests, including:

  • a blood test called immunophenotyping, to detect the presence or absence of different white blood cells (this tells if you have T-cell or NK-cell LGLL)
  • a bone marrow test
  • scans to monitor the impact of LGLL on other organs in your body.

You’ll have more blood tests during follow-up appointments to monitor your body’s response to LGLL and to check if you need treatment.

Treatment and side effects

As LGLL is usually a slow developing (chronic) condition, many people may not notice symptoms for a while. Some people may be placed on 'watch and wait' until they do need treatment. This will mean you won’t start treatment straight away – instead you’ll be monitored with regular tests and only start treatment when you need to. However, as a result of frequent infections, the majority of people (60%) with LGLL will eventually need treatment.

Currently there’s not one standard form of treatment for LGLL, so it’s important to speak to your healthcare team to find out which treatment is best for you.

The drugs used for treating chronic LGLL are designed to lower the activity of your immune system. They are not aggressive cell-killing drugs. This means that the side effects are usually mild, but different treatments will have different side effects. You can always speak to your specialist or healthcare team about the possible side effects of a particular treatment.


Although it’s not possible to cure LGLL at the moment, most people (87%) who do have treatment generally respond well and have a good quality of life.

People with LGLL have a higher risk of developing infections which in very rare cases can be fatal. Having treatment – when you need it – lowers this risk.

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