Introduction

Managing follicular lymphoma is a significant challenge for clinicians because of its inevitable tendency to relapse. This condition is generally considered incurable and is manageable as a chronic disease. The current conventional approach to treatment has not been successful in eliminating the disease. Therefore, in the majority of patients, this cancer is characterised by phases of relapse and remission.¹

Minimal residual disease (MRD) detection has emerged as a ray of hope in treating this condition. MRD monitoring has a significant role in disease management and improving patient outcomes. Studies have shown that MRD assessment is an important factor in long-term disease control in follicular lymphoma.²

This article will focus on MRD, its importance in follicular lymphoma, its detection, and how it influences treatment decisions.

What is follicular lymphoma?

Follicular lymphoma is a form of non-Hodgkin lymphoma. It is a type of blood cancer. This cancer affects white blood cells called B-lymphocytes. These B cells become abnormal and multiply uncontrollably, forming tumours in the lymph nodes or other body organs. It is typically an indolent (slow-growing) lymphoma. This cancer is classified into four stages, 1-4, based on the spread of the disease. This classification determines the treatment options for patients.³  

Signs and symptoms

Common symptoms include generalised, painless lymphadenopathy (swelling of lymph nodes) in the armpit, neck, or groin regions. Other symptoms are fever, weight loss, and night sweats. Often, many patients show no symptoms, and the condition is diagnosed during a general clinical examination. ³

Treatment

Treatment of follicular lymphoma depends on the patient’s condition and involves various approaches depending upon the disease stage. Different treatment options include radiation therapy, chemotherapy, antibody therapy, immunochemotherapy (a combination of chemotherapy and antibody therapy), radiation therapy in combination with immunochemotherapy, etc. Treatment is not immediately given to asymptomatic patients. A watch-and-wait strategy is adopted, which means treatment is delayed until necessary.³

What is minimal residual disease?

Minimal residual disease is a term used for the small number of cancer cells that remain in a patient’s body after treatment. It is also known as measurable residual disease. These cells are a significant concern in cancer treatment because they can potentially cause disease relapse. These cells are too limited to be detected through standard methods such as microscopes, imaging scans, or blood tests. MRD can only be detected using highly sensitive techniques that can identify one cancer cell among many normal cells.⁴

^{How is MRD detected?}

Techniques for detecting MRD include polymerase chain reaction (PCR), flow cytometry, and next-generation sequencing (NGS).

These techniques use peripheral blood (drawn from veins) and bone marrow cell samples. Bone marrow cells are obtained by a procedure called bone marrow aspiration. In this procedure, a small amount of liquid marrow is extracted by inserting a needle into the bone.

A positive MRD finding shows that there are still cancer cells after treatment, while a negative MRD result indicates that there are no cancer cells present.

Techniques for detecting MRD

• Polymerase chain reaction (PCR)

 PCR is a technique in which a part of DNA is amplified to study it in detail. PCR targets specific genetic markers. Follicular lymphoma targets BCL2/IGH rearrangement. This marker is considered a genetic hallmark of follicular lymphoma. Different types of PCR techniques are used, such as quantitative PCR (qPCR) and droplet digital PCR (ddPCR). The PCR technique is a sensitive and clinically helpful method for MRD detection.⁵  

•  Flow cytometry 

The process of flow cytometry involves staining cells with a light-sensitive dye and then immersing them in a fluid. These fluid-containing cells are then placed in a flow cytometer machine and passed through a light beam. These cells are analysed to identify immunological markers on the surface of cells. This helps in the 

identification of immunophenotypic abnormalities. It is an established method for identifying MRD in other forms of non-Hodgkin lymphomas. However, its use in follicular lymphoma is not yet established.^5,6

• Next-generation sequencing (NGS) 

 NGS is an advanced technique with a higher rate of sensitivity and specificity. It can detect even minor mutations and assess multiple genes simultaneously. This technique is also known as massively parallel sequencing. However, its use is not yet standardised due to a lack of guidelines.^{5, 7}

Why is MRD important in follicular lymphoma?

Routine monitoring for minimal residual disease (MRD) is increasingly becoming common in clinical practice. MRD testing on a regular basis helps doctors make better therapeutic decisions. Research has shown that those patients exhibiting MRD-negative results demonstrated improved progression-free survival compared to MRD-positive individuals. This highlights the importance of sustained negative MRD status over time.^8,2 MRD assessment has a significant role in disease management and improving patient outcomes. It is crucial to monitor and treat these cells because they can lead to disease relapse. Therefore, MRD monitoring after the initial treatment of follicular lymphoma holds significant importance. Clinical implications of minimal residual disease include:

Identifying early signs of relapse

The key benefit of MRD testing is its capability to detect early signs of relapse. Residual cancer cells are often undetectable using conventional diagnostic methods like imaging or standard lab tests, which leads to a delay in recognising disease recurrence. However, highly sensitive test methods used to detect minimal residual disease help in the early detection of relapse and allow for timely intervention.^8,2 

Assessing the effectiveness of treatment 

The MRD status is helpful in determining the efficacy of a therapy. If the MRD test results show a reduction in the level of these cells, it means that treatment was effective, while unchanged or increasing levels suggest the need for a therapy adjustment.²

Prognostic indicator

MRD status is a crucial factor for predicting progression-free survival in patients with follicular lymphoma. Studies have shown that patients who achieve MRD-negative status after treatment have significantly longer progression-free survival compared to those who remain MRD-positive.^{8, 2}

Tailoring treatment plans

Test results aid in making personalised treatment plans based on the MRD status of individual patients. The various treatment approaches followed are:^{8, 2}

• Adjusting treatment intensity

If MRD is detected after initial therapy, a more aggressive treatment approach is adopted to eliminate these residual cells. Depending on the patient’s condition, doctors use high doses of chemotherapy or a combination of therapies. Conversely, if patients obtain MRD-negative results it means they may not require further aggressive treatment. This personalised approach helps in attaining prolonged remission periods.

• Reducing unnecessary treatment

MRD testing helps identify patients responding well to initial treatment. Therefore, MRD status can help doctors determine if a more conservative approach can be followed, thus sparing the patients from complications linked to intensive therapies.

• Guiding maintenance therapy

The objective of maintenance therapy is to sustain positive treatment outcomes. MRD testing during maintenance therapy helps clinicians monitor the efficacy of the treatment so that they can make timely adjustments to control the disease.

What are the ways to educate and support patients with MRD?

Various ways to educate and support patients with MRD include:⁹

• Counselling services to manage feelings of anxiety and uncertainty linked with MRD
• Joining cancer support groups can assist patients in coping with mental and emotional challenges more effectively
• Getting access to various educational resources to understand the concepts of minimal residual disease. This will help patients understand the importance of MRD monitoring and its implications in treatment

Patients can utilise a combination of these educational and support strategies. These services will assist them in gaining a better understanding of the condition. It will help them adhere to treatment plans and maintain a higher quality of life.

Summary

MRD testing is an important breakthrough in the field of oncology. This advanced diagnostic tool has revolutionised the management of various cancers, including follicular lymphoma. MRD monitoring has played an essential role in longer remission periods and improved survival in follicular lymphoma. MRD can only be detected using highly sensitive techniques. MRD monitoring has a significant role in clinical practice, such as identifying relapses at an early stage, assessing the effectiveness of treatment, playing an important role as a prognostic indicator, aiding clinicians in making more personalised decisions and tailoring treatment plans based on the MRD status of individual patients. The future of MRD testing in follicular lymphoma seems promising as this field is continuously growing. Advancements aim to bring better MRD testing tools with improved sensitivity and specificity. These developments will enable more personalised and effective treatment strategies. Continual advancements in MRD detection techniques and their integration into routine clinical practice will ultimately improve patient outcomes and quality of life.