The present data indicate that the MMR is not playing any role in cell response to 5FU treatment and suggest that MMR status of tumours in patients with CRC is not a suitable predictive marker to 5FU therapy. Our finding suggests that patients with fast-growing tumour may respond better than patients with slow-growing tumours to 5FU therapy. The present work emphasizes that the proliferation speed of tumour must be considered in predicting response to 5FU therapy.