Characteristics
Follicular lymphoma (FL) is a slow-growing or indolent form of non-Hodgkin lymphoma (NHL) that arises from B-lymphocytes. These B-lymphocytes are a type of white blood cells that produce antibodies to target viruses, bacteria, cancer cells, and other foreign substances. The term ‘follicular’ refers to the fact that the abnormal B cells in FL usually develop in clumps, or ‘follicles’ inside lymph nodes.
FL is the most common type of low-grade NHL. It can develop at any age, but it is more common in people older than 60 years. In most cases, the cause of FL is unclear. However, there is an established association between FL and conditions that affect the immune system, such as auto-immune disorders, HIV, or the use of immunosuppressive medication following an organ transplantation. In 2021, about 200 patients were diagnosed with FL in Belgium.
While FL follows an indolent disease course in most patients, it can transform into a more aggressive type of NHL, such as diffuse-large B-cell lymphoma (DLBCL).
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Symptoms
FL is usually slow-growing, and symptoms typically develop gradually over time. Some patients do not experience any symptoms and the disease can be detected during tests for a different health issue.
The most common symptom of FL is a painless swelling of lymph nodes. These swollen lymph nodes can develop in any area of the body, but most commonly occur in the neck, armpit, or groin. In addition to this, FL can be associated with fatigue. Some patients with FL may also experience so-called ‘B-symptoms’, although this is far less common than in patients with more aggressive NHL subtypes. These B-symptoms include heavy sweating during the night, fever, and an unexplained weight loss over short a period of time.
In FL patients with bone marrow involvement (about 50%), a disturbed blood cell production may lead to shortness of breath and fatigue, an increased risk of infections and a tendency to bleed or bruise easily. FL may also manifest itself outside of the lymph nodes (‘extranodal’ lymphoma). Depending on the location of these extranodal manifestations, patients can experience a variety of symptoms.
Diagnostic tests
The diagnostic process for FL starts with a physical examination, during which the doctor palpates lymph nodes and other areas of the body to check for swelling. The doctor will also assess the medical history of the patient to better understand the general health status and any potential risk factors. If a FL is suspected, a lymph node biopsy is performed to make a final diagnosis. This is a simple procedure during which all, or part of a suspicious lymph node is removed from the body and sent to the laboratory for a microscopic evaluation. If this analysis is indicative for FL, additional tests can be performed to assess how far the cancer has spread. This includes blood tests and imaging tests to look for signs of FL in other areas of the body (X-ray, CT, PET, MRI, ultrasound). To better characterize the exact FL subtype, genetic and/or molecular assays can be performed on FL cells in the blood or bone marrow.
Treatments
In patients who do not exhibit symptoms of FL, physicians usually opt for a ‘watch-and-wait’ strategy. This means that no treatment is initiated, but that the patient is closely monitored to see if the disease progresses.
For patients with limited disease, radiotherapy to the affected lymph nodes is often able to control the disease for an extended period of time. For patients with more advanced disease who exhibit symptoms, the initial treatment usually consists of a monoclonal antibody (e.g., rituximab or obinutuzumab) in combination with chemotherapy (e.g., bendamustine, a combination of cyclophosphamide, doxorubicin, vincristine, and dexamethasone [CHOP]). If this treatment leads to a remission, patients often receive additional therapy to delay the lymphoma from coming back (relapse). This treatment phase is referred to as maintenance therapy and usually consists of rituximab, or obinutuzumab monotherapy. Rituximab may also be used as monotherapy in patients with advanced-stage, low-grade FL.
While the initial treatment for FL is usually effective, the disease remains to be incurable, and most patients will eventually suffer a relapse. The treatment for patients with relapsed disease depends on the treatment that was given in first line, how the patient responded to this treatment and how quickly the relapse occurred. Possible treatments for patients with relapsed FL (and for patients who do not respond to the initial therapy [refractory patients]), include rituximab or obinutuzumab alone, or in combination with chemotherapy, the combination of rituximab and the immunomodulating agent lenalidomide (R2), or radiotherapy. If second line therapy leads to a good remission, a stem cell transplantation can be considered for fit patients. In addition, also bispecific antibodies represent a promising new treatment modality for patients with indolent lymphoma, including FL. Finally, participation to clinical trials may offer the opportunity to be treated with new therapies.
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