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About CLL, SLL and MBL

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Diagnosed with Chronic Lymphocytic Leukaemia? So, what now?

The following is a brief guide to CLL, and we also explain the relationship with SLL and MBL. You can find more detailed information in other places on this website.

When you are newly diagnosed, it can be a huge shock and you are bound to feel anxious and afraid. But the first thing to say is that there are many promising treatment options for CLL and, very likely, you will have many long years ahead of you. Many patients live with CLL for decades and stay active and, importantly, have a good quality of life.

We suggest that you take time to learn about your disease – there’s lots to learn – and a good place to start is right here. We set out below some of the basics of CLL and point you to further information for when you are ready. Knowing more about CLL will help in your discussions with your consultant and medical team. So, let’s start.  Have a look at these short animations, which explain about diagnosis and the period known as ‘Watch and Wait’ or ‘Active Monitoring’.

What is Chronic Lymphocytic Leukaemia?

Chronic lymphocytic leukaemia (CLL) is a form of cancer that affects the blood — specifically a type of white blood cells called lymphocytes — and bone marrow.

CLL is the most common leukaemia in adults. Many people are symptom-free when they learn they have the disease. The good news is that CLL has a survival rate that is higher than many other cancers.

While it’s true that there is no known cure for CLL, many cases are very slow to spread. If you are diagnosed with a more aggressive form of the disease, there is also much hope, as every year brings newer, more effective treatments that can extend both the quality and quantity of life.

More about how CLL is diagnosed can be found here.

What is MBL?

You may have been diagnosed with a condition known as MBL, and here we explain what it is, and its relationship to CLL and SLL.

MBL (monoclonal B-cell lymphocytosis)  is a type of disorder of white blood cells known as B-cells. The medical term for these cells is lymphocytes. In MBL, some of these B-cells have developed abnormally and are known as monoclonal lymphocytes. This just means that they have developed from a single original cell, but they do not operate in the blood as normal B-cells.

There are two types of monoclonal lymphocytes known medically as Low-count and High-count. Low-count does not progress to a disease, whereas High-count may.

MBL tends to increase with age. It can be as high as 20% in otherwise healthy people older than 60 years and as high as 75% in subjects older than 90 years.

What causes MBL?

There is some research that indicates that it may be the result of a viral infection at some time in the past. There also may be an inherited genetic predisposition in some cases, but research is still needed to fully understand this.

How is MBL diagnosed?

You will have had a sample of blood taken, probably for your doctor to check something not related to MBL. This blood test showed up an abnormal number of monoclonal lymphocytes and to confirm a diagnosis, you will usually have another test, or tests, after a few months. You may have annual checks after this.

Will my MBL develop?

If you have been diagnosed with High-count MBL there is a chance that it could develop into Small Cell Lymphoma (SLL) or Chronic Lymphocytic Leukaemia (CLL). However, any progression is usually slow, and you will be monitored regularly to see if there has been any change.

What if it does change to SLL or CLL?

Both these conditions are usually slow growing and are very manageable with modern treatments. The medical policy is to wait until treatment becomes necessary, rather than treat at an early stage. This is usually referred to as Active Monitoring or Watch and Wait.

It is very likely that you will be able to lead a normal life, and around 30% of patients will never need treatment. SLL and CLL are slightly different versions of the same disease and are treated in the same way.

You may like to learn more about SLL and CLL and you can find out everything you need to know in the following sections.


In conclusion, there is a good chance that your diagnosis of MBL may never develop. If it does, it could still not become serious enough to need treatment. If treatment is required, current excellent options are available which mean that you could expect to live a normal lifestyle.


What is Small Cell Lymphoma (SLL)?

SLL was once thought to be a separate disease to CLL, but they are now regarded as the same disease.

The difference between SLL and CLL is where the blood cancer is located. CLL has most of the cancerous B lymphocytes in the bloodstream, whereas SLL has most of the cancerous B lymphocytes in the lymph nodes and lymphoid tissue such as the spleen and the tonsils.

SLL and CLL can be coupled together and are usually expressed as CLL/SLL.

The first sign of SLL is usually a painless swelling in the neck, armpit or groin which is caused by enlarged lymph nodes due to infiltration of normal lymph nodes by the cancerous B-cells. Other symptoms of SLL are similar to CLL (see below).

Diagnosis and treatment of CLL and SLL are the same, and where you see CLL on this website, we are referring to both conditions.


CLL Symptoms

Most CLL patients do not have any symptoms on diagnosis, but these can develop if the disease progresses. Here are some of the main symptoms to look out for.

The four major symptoms of CLL are night sweats (where the bed can become soaked and may need to be changed several times a night), fevers and chills, unexplained weight loss, and general fatigue (this is more than just feeling a bit tired and can be complete exhaustion).

CLL symptoms may also include bone pain, easy bruising, and bleeding, swelling of lymph nodes under your arms or in your neck or groin, and swelling of your abdomen, particularly your spleen. Frequent infections can also be a problem. These symptoms will be taken into account when treatment is being considered. You can find more about treatment here.

This may sound frightening at first, but don’t panic. Not all these symptoms occur in all cases. It’s also important to remember that for many patients, CLL symptoms won’t appear until several years after an initial diagnosis.

You should inform your consultant of any changes you experience so that you can be monitored.

CLL Causes

The exact cause of CLL is unknown, but scientific advances are helping researchers develop a fuller understanding of the disease.

CLL Risk factors

These factors may increase the risk of CLL:

Gender has also been noted as a potential risk factor for CLL. More men than women are diagnosed with the disease, but the reasons for this are unknown.

I have blood cancer. Why am I not being treated?

Good question. Because CLL is often very slow in progressing, there is no benefit in treating most patients when they are diagnosed. Some, roughly a third, will never need treatment, whilst another third won’t need treatment for several years. The final third of patients will need early treatment.

All treatments have side effects, and it is considered best to put most patients on a system of medical monitoring, also known as ‘Watch and Wait’. This means that you will be seen regularly by your medical team, who will carefully assess you to see how your disease is behaving. They will look at what stage your CLL is.  See more below.

CLL Staging

Once diagnosed, your consultant will ‘stage’ your CLL. Staging is used to describe where the CLL is located and the extent to which the CLL is affecting the blood count and the number and size of lymph nodes. Staging CLL in this way helps your consultant to predict how quickly the cancer may grow and to keep track of it.

More about staging here.

Emotional support

As we said earlier, being diagnosed with CLL can be a huge shock. People react in many ways, but you may feel depressed, or even in denial: “It can’t be happening to me!” These are quite normal reactions and will usually subside as you learn more about the disease.

Many people feel the need for emotional support, and we have developed a special tool to help. Some of our members have found it to be very beneficial. You can find it here.

Other support

If you need to speak to someone, we have a helpline: 0800 977 4396. You can be sure of a sympathetic ear and sound advice.

Our online forum is a very good source for the latest information about CLL and you are certain to get a warm welcome from the community. You will need to join, and you can do so here.

Learning about your CLL can really be of benefit to you. It helps you to recognise any changes in your body and to discuss treatment plans with your consultant if this is needed.

As a CLL patient, you are entitled to free prescriptions. You can find out more here.

You have started on your CLL journey. We wish you well and don’t forget that we are to help.

CLL Overview & Treatment

CLL Overview

We asked two of our leading CLL doctors to give an insight into the working of Multi-disciplinary Team (MDT) meetings


Over a relatively short time period a remarkable number of effective new therapies have been developed for patients with CLL.

Living with CLL/SLL

Kevin and Sue Powell share their experience of CLL at our Bournemouth Conference

Find out more about the experiences of some of our members by watching this video.

Click here to go to our online community

What is smoldering CLL?

In the video to the right Gwyneth Stafford CLL & Lymphoma Nurse Specialist at Cambridge University Hospitals discusses managing infections and goes on to the challenges that CLL patients experience when managing their symptoms. A theme running through these videos is the importance of keeping the medical team informed and working together to find strategies and support to reduce impact.