Chemotherapy-induced thymidine phosphorylase modulation in colorectal cancer

Abstract

e15050 Background: Thymidine phosphorylase (TP) is an inducible enzyme responsible for nucleoside metabolism, antiapoptosis activity, and promotion of angiogenesis. In addition, conversion of the prodrug capecitabine (C) to its active form depends on TP activity. Preliminary evidence suggests that TP immunohistochemical expression may predict benefit from first-line treatment of metastatic colorectal cancer (CRC) with C plus irinotecan. Several chemotherapeutic agents have been shown to modulate TP expression. The aim of the present analysis was to verify if TP expression differs among primary and paired metastases in CRC patients, or may vary depending on patients’ exposure to chemotherapy. Methods: TP expression was evaluated by immunohistochemistry (clone p-P-GF.44C, Abcam, Cambridge, UK) in a series of 120 primary CRC and their matched distant metastases. Tsuda's scoring system was adopted, defining TP expression as negative (score 0–1) or positive (score 2–3). Results: Data on the first 57 patients are here presented. Sites of biopsied metastases were liver (n=41), lung (n=10), and peritoneum (n=6). Metastases were asynchronous in 42% of patients. Higher TP expression was observed in primary cancers than in metastases (36.8% vs. 15.8%, p=0.007). Among patients who received at least one cycle of chemotherapy before metastasis sampling (38.6%), a TP expression decrease was demonstrated in only 13% of metastatic samples. Oppositely, a significantly higher proportion of untreated patients lost TP expression in metastasis sites (36%, p=0.01). Conclusions: In advanced CRC patients, TP expression tend to decrease in metastases, particularly in those patients who did not receive chemotherapy before metastatic sampling. Although intratumoral heterogeneity and other causes of discrepancy cannot be excluded, true chemotherapy-induced modulation of TP may be hypothesized. No significant financial relationships to disclose.