This article, by Oncologist and lymphoma treatment expert answers the most frequently asked questions regarding a new form of treatment known as radioimmunotherapy. This will be of interest to anyone suffering from lymphoma who would like to know what the latest treatment options are.
- What is radioimmunotherapy?
- What are monoclonal antibodies?
- What are the advantages of radioimmunotherapy?
- What type of radioimmunotherapy is used to treat lymphoma?
- How is radioimmunotherapy given?
- What are the side effects of radioimmunotherapy?
- Is radioimmunotherapy a cure for follicular lymphoma?
Radioimmunotherapy (RIT) is a cancer therapy that involves the use of targeted radiotherapy, which is delivered directly to lymphoma cells by a monoclonal antibody. The radiotherapy is delivered in the form of a radioactive particle or ‘radioisotope’ that is attached to the antibody.
Antibodies that are designed to be identical to one another and to recognise one single target are called ‘monoclonal’ antibodies (mAbs for short). The monoclonal antibody used for lymphoma treatment is specially manufactured to recognise an antigen on a particular kind of lymphocyte – the B lymphocyte or B cell. This antigen is called CD20 and it is found on most B cells. When the monoclonal antibody recognises the antigen on the surface of the cell, it attaches itself to it. As monoclonal antibodies target the B cell, they are only used to treat lymphomas that have developed from B cells. Most monoclonal antibody therapies use just the antibody alone, or the antibody in addition to chemotherapy. The most common monoclonal antibody used for treating lymphoma in this way is rituximab (MabThera®). Radioimmunotherapy is different from this kind of monoclonal antibody treatment in that it attaches radiation to the monoclonal antibody.
The targeted radiation comes from a tiny radioactive particle or radioisotope, which is bound to the monoclonal antibody using a strong chemical bond. This bond enables the radioisotope to stay connected to the monoclonal antibody and to deliver the radiation to kill the lymphoma cells. Another advantage of radioimmunotherapy over monoclonal antibody therapy used on its own is that the radiation kills the surrounding tumour cells and not just the cells the monoclonal antibody attaches to. This process is sometimes referred to as the ‘crossfire’ or ‘bystander’ effect.
The radioimmunotherapy approved for use in lymphoma in the UK is called Zevalin®. This is a combination of a monoclonal antibody called ibritumomab and a radioisotope called yttrium-90. It is approved for use in people with follicular lymphoma that has relapsed following treatment with rituximab and/or rituximab plus chemotherapy. More recently, the drug has been approved for use as a consolidation therapy in patients who have completed initial chemotherapy as their first-line (initial) therapy for follicular lymphoma. Zevalin® has also been used for other types of lymphoma in clinical trials in Europe and in the US.
Radioimmunotherapy is given on an outpatient basis in larger hospitals that have a nuclear medicine department. It is given by healthcare staff who have been specially trained to give this treatment. Rituximab is given prior to receiving Zevalin® as a drip inserted into a vein in the arm. It takes about 60–90 minutes to administer and you will be able to go home after this if you are feeling well.
After 7–9 days you come back to have another treatment with rituximab. This is immediately followed by the Zevalin®, which is administered through the same drip. This takes about 10 minutes and is given in a radioisotope therapy room, usually in a nuclear medicine department.
About a third of people experience mild flu-like symptoms, including weakness, chills, fevers, aches and pains. These side effects are usually easy to treat and should not last long (usually around 24–48 hours). Zevalin® can lower the numbers of healthy cells in your blood, in particular your platelets and white cells, rarely the red blood cells. The most common problem is a low platelet numbers that can lead to a tendency to bruise easily and rarely bleeding. Such low counts may require a platelet transfusion and can sometimes it can take between 8 and 12 weeks to recover after the Zevalin® treatment.
Zevalin® is not considered to be a cure for follicular lymphoma, but it has produced durable remissions for some patients even in patients who are no longer responding to chemotherapy or rituximab. As with all new treatments, there are some challenges ahead for radioimmunotherapy. The safe and effective use of radioimmunotherapy needs a skilled team and special facilities, so it cannot be given in every hospital. The question of equal access to this drug for patients in all areas of the country will also need to be addressed. Currently access still varies from region to region, but doctors do refer patients across regional boundaries and they might also be able to apply for funding through the national Cancer Drugs Fund. Notwithstanding the challenges, radioimmunotherapy has the potential to be more effective than chemotherapy and there is sufficient evidence to suggest that it can be effective for many patients even when other treatments have failed.