Primary colorectal tumour is not an accurate predictor of thymidylate synthase in lymph node metastasis.

Analysis of tumour markers is helping to predict individual patient response to chemotherapy. However, the difficulties in obtaining metastatic disease samples has led to a reliance on assessment of primary tumour, with little data on its predictive ability. This study assessed thymidylate synthase (TS), a target for the commonly used drug 5FU, in 42 paired primary colorectal tumour and lymph node metastasis. High TS staining was seen in 63% of primary colon tumour cells and 81% of the secondary lymph node. Primary tumour did not have significant predictive power for secondary tumour samples (kappa=0.125; p=0.38). There was no significant relationship between TS staining and expression of G1/S cell cycle proteins p21, p27, p53, cyclin D1, proliferating cell nuclear antigen (PCNA) and retinoblastoma protein (Rb) (p>0.05 in all cases). Discordance in TS protein levels between primary and secondary tumours demonstrates the danger of predicting outcome after chemotherapy in metastatic colorectal cancer from the primary tumour.