In this “Science Simplified” series, we’ll be sharing insights from the latest research presented at the American Society of Hematology (ASH) conference in December 2025. Each article will stand on its own, explaining what was studied, what was discovered, and what it could mean for patients, while the full series will offer a bigger-picture view of where the science is heading.
Our goal is simple: to make the latest research understandable, relevant, and useful to you.
Follicular lymphoma is a slow-growing (indolent) form of non-Hodgkin lymphoma, that doesn’t always need immediate treatment. Available therapies can cause side effects, and so clinical teams often try to avoid unnecessary treatment. This means that many people who are diagnosed with Follicular Lymphoma and have no symptoms from the disease are often advised to go on active monitoring, otherwise known as “watch and wait”.
In 1997, the French Study Group on Follicular Lymphomas (Groupe d’Etude des Lymphomes Folliculaires – GELF) developed a list of markers to help doctors decide when follicular lymphoma needs treatment. Referred to as “The GELF criteria”, these identify signs that your lymphoma may need treatment now rather than later. These include:
This was an important breakthrough as researchers found patients who met fewer of these criteria (which they referred to as “low tumour burden”) often went months or years without needing any treatment. If any of these GELF criteria developed (which they refer to as “high tumour burden”) doctors would then recommend treatment.
At ASH 2025, an expert panel supported by the Follicular Lymphoma Foundation met to begin re-evaluating the GELF criteria and how they are applied in practice, to ask how to make this list of criteria even more precise. One important part of this discussion focused on whether all parts of the GELF criteria carry the same level of risk.
A large study from Memorial Sloan Kettering Cancer Center looked at over 2,000 patients with follicular lymphoma. Interestingly, it found that only certain GELF features were linked to a higher risk of early death and indicated a higher priority for treatment.
These high-risk criteria were: B symptoms (such as fevers, night sweats, or weight loss), low blood counts (cytopenias) and fluid buildup. Their study found that other GELF criteria (listed above) did not appear to carry the same risk.
This raised an exciting area for further research: Could some patients who technically meet GELF criteria still be safely observed under active monitoring? While this work is still ongoing, it reflects a growing effort to make treatment decisions more personalized and less “one-size-fits-all.”
Another interesting area of research presented at ASH25 included: for those low-tumour burden FL patients who are treated, can we do better?
Previous studies gave patients only the immunotherapy drug rituximab (a monoclonal antibody), without chemotherapy. While these studies showed that treatment could keep the lymphoma under control for longer periods, it did not improve overall survival. Many patients ended up receiving treatment when they may never have needed it.
At ASH 2025, researchers reported results from a study led by Villasboas involving 101 patients with untreated, low-tumor burden follicular lymphoma, given a different type of immunotherapy, a bispecific antibody called mosunetuzumab. We hear from patients the impact of watch & wait can have on people’s mental health, so we were keen to understand more about this study.
We often hear how watch & wait can impact a patient’s mental health, so when results from a study involving 101 patients with untreated, low-tumour burden FL were reported at ASH 2025, we were keen to learn more. Led by Dr. Villasboas (Mayo Clinic, US), the study was of patients given mosunetuzumab, a different type of immunotherapy with a bispecific antibody.
While most patients responded to treatment and 93% remained free of disease progression one year later, it is important to look at the whole picture (see previous blog “How to make sense of research”). This study was not very large and had a relatively short follow-up time, which matters even more in a slow-growing disease like FL. We know from earlier studies treating low-tumour burden FL patients with rituximab, that just because a patient responds well to treatment it doesn’t necessarily mean better outcomes in the longer term.
The study also found a high rate of infections (13% having serious infections) which means experts agree that mosunetuzumab should currently only be used in clinical trials for patients with low-tumor burden FL. However, a bigger trial is now comparing mosunetuzumab to rituximab and results from this will help clarify whether newer treatments truly offer advantages over watch & wait.
The most important takeaway from ASH 2025 is reassuring: active monitoring remains a safe and appropriate standard of care for many people with low-tumor burden FL.
We remain interested to see the research continue to explore how this approach can be used with more precision. There are still several areas to understand more deeply – how to use current diagnostic and prognostic criteria more effectively, the long-term effects of earlier treatment, how to better predict which patients will benefit the most from early treatment, and more.
For now, if your doctor recommends watch & wait, it is because this approach is backed by strong evidence.
Want to know more? Watch our recent webinar about watch and wait here:
For the full technical report, find our Chief Medical Officer’s article here:
Acknowledgements
These articles are supported by sponsorship from AstraZeneca, Genmab, AbbVie, Ipsen and Incyte.
All of the above have had no influence on, control of, nor input into the development or content of any article
