The health of the thymus is associated with cancer patients’ outcomes to immune checkpoint inhibitor treatment, according to a ground-breaking international study reported at the recent ESMO Congress 2025.
“Immune checkpoint inhibitors have transformed cancer treatment, but responses remain limited in some patients,” said lead author Dr Simon Bernatz, Artificial Intelligence (AI) in Medicine Programme, Mass General Brigham, Boston, US. He noted that current biomarkers for immunotherapy, such as PD-L1 or tumour mutational burden, focus on tumour characteristics, but largely overlook patients’ immune capacity.
The new study investigated whether thymic health might be associated with response to immunotherapy by analysing routine chest CT scans from nearly 3,500 real-world patients treated with immune checkpoint inhibitors. Using an AI tool based on a deep learning framework developed to carry out multi-layered analysis of data from CT scans, researchers assessed thymic size, shape, and structure to score thymic health, and examined how these scores related to patients’ outcomes with immunotherapy.
Results showed that higher thymic health was associated with a 35 per cent lower risk of cancer progression (hazard ratio (HR) 0.65; 95% CI 0.54-0.77) and 44 per cent lower risk of death (HR 0.56; 95% CI 0.46-0.68) in the group of just over 1,200 patients with non-small cell lung cancer included in the study. There was also a positive association between thymic health and immunotherapy outcomes in patients with other cancers, including melanoma, renal, and breast cancers.
A further part of the study confirmed that the deep learning analysis of CT scans provided a valid proxy for thymic health.
“Immunotherapy relies on unleashing T-cells and the thymus is where T-cells are matured. Our study shows that thymic health is associated with improved immunotherapy outcomes across diverse cancer types,” explained Dr Bernatz.
Looking to the future, he believes the findings suggest that thymic health could serve as a non-invasive biomarker of adaptive immune competence in a range of different cancers.
“Thymic health has the potential to enhance patient stratification in precision oncology,” he suggested. “Randomised clinical trials will be needed to establish this in clinical practice. But we think thymic health is one of the missing pillars from current cancer biomarker panels and can start bringing the patient’s immune system into clinical decision making alongside established tumour-centred biomarkers.”
The main limitation of the finding is that it has not been validated prospectively, said Dr Alessandra Curioni-Fontecedro, Professor of Oncology, University of Fribourg, Switzerland, not involved in the study. “We need a prospective study including evaluation of thymic health in patients undergoing immunotherapy.”
However, she noted that the inclusion of a validation cohort added to the study’s quality and that, although thymic health is not routinely assessed, chest CT scans are commonly performed in patients with cancer.
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