Chronic lymphocytic leukaemia that no longer responds to treatment, known as refractory disease, or returns after a period of remission, called relapsed disease, presents a significant challenge for patients and their healthcare teams. While treatments have improved dramatically in recent years, understanding what happens when the disease progresses and knowing the available options can help patients navigate this difficult phase of their journey.

Understanding Relapsed and Refractory Chronic Lymphocytic Leukaemia

When someone with chronic lymphocytic leukaemia experiences disease progression after treatment, they fall into one of two categories. Relapsed disease occurs when someone who previously achieved a complete or partial response to treatment shows evidence of disease coming back after six months or more.^[1] The disease may return after a long period of complete remission following initial treatment, or within months after a partial response to second or third-line therapy.

Refractory disease describes a situation where the leukaemia does not respond adequately to treatment, or where the response is very short-lived. This can happen with any line of therapy and indicates that the cancer cells have found ways to resist the medications being used.^[3]

Chronic lymphocytic leukaemia is characterised by a pattern of relapses and remissions, meaning that even after successful treatment and prolonged periods without symptoms, the disease often returns. This chronic, relapsing nature means many patients will receive multiple lines of treatment throughout their lives.^[1] The goal of treating relapsed or refractory disease is not typically to cure the condition, which remains largely elusive, but rather to control the disease, delay progression, and maintain quality of life.^[1]

How Common Is Relapsed or Refractory Disease

Chronic lymphocytic leukaemia predominantly affects older adults and is one of the most common types of leukaemia in Western countries.^[1] The disease typically occurs during or after middle age and rarely affects children.^[2] As patients live longer with improved treatments, the likelihood of experiencing relapse increases.

Even with modern frontline treatments, relapse is common. For example, after treatment with fludarabine, cyclophosphamide, and rituximab—one of the most frequently used first-line combinations—approximately six percent of patients relapse within six to twelve months, and a further fourteen percent do so within two years.^[1] These statistics highlight that while treatments can be effective, they rarely provide permanent disease control.

The pattern and timing of relapse varies considerably between patients. Some individuals may remain stable and symptom-free for years before their disease progresses, while others may experience more rapid progression. Multiple factors influence how quickly and aggressively the disease returns, including the genetic characteristics of the leukaemia cells and how well the disease responded to previous treatments.

Why Does Chronic Lymphocytic Leukaemia Relapse or Become Refractory

The development of relapsed or refractory disease stems from the cancer cells’ ability to adapt and develop resistance to treatments. With continuous use of certain medications, particularly covalent BTK inhibitors (drugs that block an enzyme called Bruton’s tyrosine kinase), resistance may emerge. This resistance is commonly associated with mutations in the BTK gene or other enzymes that work downstream in the same cellular pathway.^[1]

The presence of certain high-risk genetic features in leukaemia cells makes relapse more likely and often leads to more aggressive disease. Patients with features such as unmutated IGHV (a gene involved in immune function) and TP53 aberrations (changes in a crucial tumour suppressor gene) face a population of significant unmet need due to aggressive disease biology and limited durable responses to treatment.^[10]

Additionally, patients who progress after treatment with BTK inhibitors may show specific mutations in the BTK gene, particularly at a location called C481. These mutations allow the cancer cells to continue growing even in the presence of the medication that previously controlled them.^[1] The cancer’s ability to evolve and find alternative survival pathways explains why sequential treatments are often needed.

Risk Factors for Relapse and Treatment Resistance

Several factors increase the risk of relapse or the development of refractory disease. The genetic makeup of leukaemia cells plays a crucial role. Patients with deletions in chromosome 17 (del 17p) or mutations in the TP53 gene tend to have shorter remission periods. For instance, in patients treated with ibrutinib, a commonly used BTK inhibitor, those with del(17p) had a median remission duration of about 40 months, while patients without this deletion or another high-risk feature called del(11q) had remissions that had not yet been reached at the time of analysis, suggesting much longer disease control.^[9]

The number and type of prior therapies also influence outcomes. Using BTK inhibitors in earlier lines of therapy is associated with longer progression-free survival. Patients who received ibrutinib after only one prior therapy had remissions that had not yet been reached in studies, compared to 27.3 months for those who had received five or more prior therapies.^[9] This suggests that the cancer becomes more difficult to control with each successive treatment.

Patients who are “double refractory”—meaning their disease no longer responds to both BTK inhibitors and BCL-2 inhibitors (another major class of drugs)—face particularly challenging circumstances. Real-world evidence suggests that treatment options for this group have reduced durability, making disease control more difficult.^[10]

Age and overall health status also play important roles. Chronic lymphocytic leukaemia is mostly seen in older patients, and factors such as performance status and the presence of other medical conditions significantly influence treatment selection and outcomes.^[1] A patient’s ability to tolerate treatment side effects becomes increasingly important when considering options for relapsed or refractory disease.

Recognizing Symptoms of Relapsed Disease

In the early stages of relapse, chronic lymphocytic leukaemia may not cause any noticeable signs or symptoms. The disease might be detected during routine blood tests before patients feel unwell.^[2] However, as the disease progresses, several symptoms may develop that signal the need for treatment.

Common symptoms of progressive or relapsed chronic lymphocytic leukaemia include painless swelling of lymph nodes in the neck, underarm, stomach, or groin. Patients may experience persistent weakness or feeling unusually tired, which can significantly impact daily activities.^[2] Some individuals develop pain or a feeling of fullness below the ribs, which may indicate an enlarged spleen.

Fever and recurrent infections are concerning signs, as the abnormal lymphocytes produced by chronic lymphocytic leukaemia are not able to fight infections effectively. Easy bruising or bleeding may occur as the expanding population of leukaemia cells leaves less room in the bone marrow for platelets, the blood cells responsible for clotting.^[2] Some patients notice small, flat, pinpoint dark-red spots under the skin called petechiae, which are caused by bleeding.

Unexplained weight loss and drenching night sweats are also common symptoms that may indicate disease progression. These symptoms occur because the body is working harder to fight the cancer, leading to increased energy expenditure and metabolic changes.^[2] Any of these symptoms should prompt a visit to the doctor for evaluation, as they may indicate that the disease is progressing and treatment may be needed.

Changes in the Body During Relapsed Disease

Understanding what happens in the body when chronic lymphocytic leukaemia relapses helps explain the symptoms patients experience. In this disease, too many blood stem cells become abnormal lymphocytes, specifically B lymphocytes. These abnormal cells may also be called leukaemia cells.^[2] When the disease relapses, the number of these abnormal cells begins to increase again.

The leukaemia cells are not able to fight infection effectively, which is why patients with progressive disease are more vulnerable to infections. As the number of leukaemia cells increases in the blood and bone marrow, there is progressively less room for healthy white blood cells, red blood cells, and platelets.^[2] This crowding effect in the bone marrow leads to multiple problems throughout the body.

The reduction in healthy white blood cells makes it harder for the body to fight off bacteria, viruses, and other pathogens, leading to frequent infections. A decrease in red blood cells results in anaemia, causing fatigue, weakness, and shortness of breath because the body cannot deliver enough oxygen to tissues. When platelet numbers drop, patients experience easy bruising and bleeding because their blood cannot clot properly.^[2]

The leukaemia cells can also accumulate in lymph nodes throughout the body, causing them to swell. When these cells collect in the spleen, an organ in the upper left part of the abdomen, the spleen enlarges and may cause discomfort or pain. The body’s immune system attempts to fight the cancer, but this constant battle leads to fatigue and the production of substances that can cause fever and night sweats.

Current Treatment Approaches for Relapsed or Refractory Disease

The treatment landscape for relapsed or refractory chronic lymphocytic leukaemia has changed dramatically over recent decades. Targeted therapies have now become the preferred standard of care, showing superiority over traditional chemoimmunotherapy (combinations of chemotherapy and antibody-based drugs) in terms of survival advantages.^[1]

Two main classes of targeted therapy are currently used: continuous BTK inhibitors and fixed-duration treatment with venetoclax (a BCL-2 inhibitor) combined with anti-CD20 monoclonal antibodies. Both classes are effective for relapsed and refractory disease, though they differ in potential side effects and how they are administered.^[3] These treatments may be used in either sequence, although few randomized studies have directly compared their use in sequential order.

Second-generation BTK inhibitors, including acalabrutinib and zanubrutinib, have shown improved safety profiles compared to the first BTK inhibitor, ibrutinib.^[1] These medications work by blocking the BTK enzyme, which is crucial for the survival and growth of leukaemia cells. Patients typically take these drugs continuously until the disease progresses or side effects become unmanageable.

Newer non-covalent BTK inhibitors, such as pirtobrutinib and nemtabrutinib, are showing promising results for patients whose disease has become resistant to earlier BTK inhibitors. These drugs work differently from covalent inhibitors and can remain effective even when mutations develop at the C481 location of the BTK gene.^[1] In the phase 3 BRUIN-321 trial, pirtobrutinib demonstrated prolonged progression-free survival, with a median time to next treatment of approximately two years, even in heavily pretreated patients.^[10]

Emerging and Investigational Therapies

The therapeutic armamentarium for relapsed or refractory chronic lymphocytic leukaemia continues to expand with several promising approaches currently being studied. Chimeric antigen receptor T-cell therapy, commonly known as CAR T-cell therapy, has shown significant activity for relapsed and refractory disease and has recently received regulatory approval for chronic lymphocytic leukaemia.^[1][3]

CAR T-cell therapy works by collecting a patient’s own immune cells, genetically modifying them in a laboratory to recognize and attack leukaemia cells, then infusing them back into the patient. While effective in select cases, its use is limited by patient eligibility, as many individuals with chronic lymphocytic leukaemia are older or have other medical conditions that may make them unsuitable candidates for this intensive treatment.^[10]

Bispecific antibodies represent another novel approach showing encouraging early-phase results. These specially designed antibodies can simultaneously bind to leukaemia cells and T cells (a type of immune cell), bringing them together so the T cells can destroy the cancer. One such antibody, epcoritamab, has achieved complete remissions in approximately forty percent of heavily pretreated patients in early studies.^[10]

BTK degrader molecules are a newer class of drugs that don’t just block the BTK enzyme but actually cause it to be broken down and removed from cells. These agents have demonstrated clinical activity even after patients have progressed on non-covalent BTK inhibitors, suggesting they may provide options when other treatments fail.^[3][10]

Another area of active investigation involves measurable residual disease (MRD) assessment. This highly sensitive testing can detect very small numbers of leukaemia cells that remain after treatment, even when conventional tests show no evidence of disease. There is mounting evidence that achieving MRD negativity—meaning no detectable leukaemia cells—improves outcomes, particularly with venetoclax-based limited-duration therapy. However, it remains to be seen whether MRD will become an established endpoint for guiding treatment decisions.^[1]

Preventing Relapse and Managing Disease Progression

While it is not currently possible to prevent relapse entirely in chronic lymphocytic leukaemia, several strategies can help optimize outcomes and potentially extend the time before disease progression. Following prescribed treatments exactly as directed is essential, as incomplete or irregular treatment may allow the cancer to develop resistance more quickly.

Maintaining overall health plays an important role in managing the disease. The interval between relapse identification and starting next-line therapy should be used to optimize both leukaemia-related issues and general health. This includes establishing adequate vaccination against common infections, as people with chronic lymphocytic leukaemia have weakened immune systems and are more susceptible to serious infections.^[3]

Regular surveillance for second primary malignancies is important, as patients with chronic lymphocytic leukaemia have an increased risk of developing other cancers. Addressing non-leukaemia-related medical conditions that may impact wellbeing and the ability to tolerate future treatments should be a priority during periods when the disease is stable.^[3]

Close monitoring through regular appointments and blood tests allows the healthcare team to detect progression early, before symptoms become severe. Early identification of relapsed or progressive disease prompts close monitoring and timely discussion about next treatment options when specific indications for treatment are met.^[3] This proactive approach ensures that interventions can begin at the optimal time.

Maintaining open communication with the healthcare team about any new symptoms or concerns is crucial. Patients should not hesitate to report fever, increasing fatigue, new or worsening swollen lymph nodes, unusual bleeding or bruising, or any other changes in their health status. These symptoms may indicate that the disease is becoming active again and requires evaluation.