A RECENT phase 2 clinical trial explored the potential of preoperative radiation therapy as a means to prime the immune system in patients with intact human breast cancers, specifically those that are oestrogen receptor-positive and HER2Neu nonamplified. The study aimed to determine whether a preoperative radiation therapy boost could significantly increase tumour-infiltrating lymphocytes (TILs) within the tumour microenvironment.
Twenty patients participated in the trial, receiving either a single fraction of 7.5 Gy or five fractions of 2 Gy, administered 6 to 8 days before surgery. Stromal TIL levels were measured using haematoxylin and eosin-stained samples, while short-term safety was assessed by monitoring time to surgery, treatment-related toxicities, and cosmetic outcomes for up to six months post-treatment.
The results revealed a statistically significant increase in stromal TILs following radiation therapy. Median TIL levels rose from 3.0% (interquartile range [IQR], 1.0-6.5) before treatment to 5.0% (IQR, 1.5-8.0) after treatment, with a P-value of 0.0037, indicating a meaningful immune response. Importantly, no patients experienced grade 3 or higher toxicities within the six-month follow-up period. Furthermore, cosmetic outcomes were favourable, with 94% of patients who underwent breast-conserving surgery demonstrating good-to-excellent results, as assessed by physicians.
These findings suggest that a preoperative radiation therapy boost can safely induce a short-term increase in stromal TILs, potentially enhancing the tumour’s immune environment. With minimal side effects and promising cosmetic outcomes, this approach could offer a feasible method for priming the immune system in breast cancer patients. Further research is needed to assess long-term effects and potential improvements in treatment response.
Katie Wright, EMJ
Reference
Shaitelman SF et al. PRECISE: preoperative radiation therapy to elicit critical immune stimulating effects-a phase 2 clinical trial. Int J Radiat Oncol Biol Phys. 2025;121(1):90-6.
