Cancer-associated fibroblasts (CAFs) are an important component of the desmoplastic stroma in rectal cancer. Preoperative chemoradiotherapy plays a pivotal role in the management of locally advanced rectal cancer. Patient-derived CAFs were used to evaluate the response to radiotherapy and its consequent impact on colorectal cancer cells (COLO320DM). COLO320DM cells were seeded and 24 hours later 1.8Gy irradiated. Subsequently, 24h later COLO320DM cells were treated with the secretome of 10x 1.8Gy irradiated CAFs or sham treated CAFs in 0.5% of serum. RNA was isolated 6 hours or 48 hours later.