Cancer-associated fibroblasts (CAFs) in the stroma play an important role in influencing the proliferation, invasion and metastasis of cancer cells. Fibroblast activation protein-α (FAP-α) is known as a marker of CAFs, while stromal cell-derived factor-1 (SDF-1) is primarily expressed by CAFs. Herein, we investigated whether the expression levels of these genes are associated with clinical outcome after pre-operative chemoradiotherapy (CRT) in rectal cancer patients. We obtained total RNA from residual cancer stroma using microdissection from a total of 52 rectal cancer specimens from patients who underwent pre-operative CRT, we performed transcriptional analyses, and the serum protein concentrations in 40 matched microdissected specimens were measured by enzyme-linked immunosorbent assay. Additionally, we sought to clarify the location of FAP-α and SDF-1 expression using immunohistochemical staining. Of the 52 patients, 15.6 and 36.8% showed detectable FAP-α and SDF-1 mRNA expression, respectively. A significant correlation was observed between stromal FAP-α and SDF-1 mRNA levels. Moreover, there was a significant correlation between stromal SDF-1 gene expression levels and serum protein levels. Patients who developed distant recurrences after CRT had positive expression of both genes (P<0.05). The positive expression of both genes was also associated with poor probability of recurrence-free and overall survival (P<0.05). Patients with elevated serum SDF-1 levels had equally poor overall survival as those with positive stromal SDF-1 gene expression (P<0.05). In immunohistochemistry, both FAP-α and SDF-1 expression was observed in certain activated fibroblasts. In conclusion, FAP-α and SDF-1 expression was shown to be involved in tumor re-growth and recurrence in rectal cancer patients treated with pre-operative CRT.

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