Thymic Health Identified as Key Predictor of Immunotherapy Outcomes

A new study presented at ESMO 2025 has uncovered a previously underappreciated factor influencing cancer patients’ responses to immunotherapy: the health of the thymus. By analyzing routine chest CT scans from nearly 3,500 patients, researchers found that thymic health is significantly associated with outcomes to immune checkpoint inhibitors across multiple tumor types.

The thymus plays a central role in the maturation of T cells, which are essential for the immune response activated by immunotherapy. Unlike current biomarkers—such as PD-L1 expression or tumor mutational burden—that focus on tumor biology, thymic health offers a window into the patient’s immune competence. This shift in focus from tumor to host may enable a more comprehensive approach to predicting treatment efficacy.

Using an AI-powered deep learning framework, the study assessed thymic size, shape, and structural integrity to develop a thymic health score. In patients with non-small cell lung cancer (NSCLC), those with higher thymic scores had a 35% lower risk of disease progression and a 44% lower risk of death compared to patients with poorer thymic health. While similar trends were preliminarily observed in melanoma, renal, and breast cancers, the data in these subgroups are more limited and require further validation.

To explore the biological basis for these imaging findings, the researchers performed T-cell receptor sequencing and immune profiling in a subgroup of 464 NSCLC patients. The results demonstrated a correlation between thymic health scores and markers of T-cell differentiation and function—suggesting that CT-based thymic assessment may serve as a non-invasive proxy for the immune system’s functional capacity, though it is not yet a validated surrogate endpoint.

While thymic health is not currently evaluated in clinical settings, the study leveraged standard chest CT scans—already part of routine cancer care—to extract this additional layer of information. This positions thymic health as a potentially accessible and cost-effective biomarker, complementary to existing molecular diagnostics.

Experts emphasize that prospective clinical trials are needed to confirm the predictive value of thymic health before it can be adopted in practice. However, the findings highlight the potential of integrating host immune readiness into treatment planning, particularly in contexts where immunotherapy is used alone or in combination with chemotherapy.

If future trials validate these observations, thymic health may eventually be incorporated into the evolving framework of precision oncology, offering another tool to refine patient selection for immunotherapy and potentially improve outcomes across a range of cancer types.