Some of the most interesting data presented at ASCO was the data on MSI and 18qLOH in a European clinical trial.
Last year at ASCO, Dr. Daniel Sargent presented new data that patients with stage II disease with microsatellite instability do not only not benefit from 5-FU, but they may be harmed, and it was recommended to test for MSI in all stage II colon cancer patients and in the presence of MSI-high not to give 5-FU. For stage III colon cancer that was not the case.
This year, the PETACC-3 clinical trial was analyzed for MSI and did not show the same the same findings. It seems that chemotherapy does not harm these patients, and they may benefit.
This has been an ongoing controversy over the last couple of years with some studies showing benefit and other not. Last year’s ASCO showed there even may be harm. What MSI means is now again up in the air. We can certainly state that the presence of MSI is a GOOD prognostic marker, meaning that these patients have a lower risk of tumor recurrence. However, if chemotherapy is beneficial or not is still not clearly answered.
Another finding in this clinical trial showed that 18q deletions are not prognostic in stage II disease when MSI status is known. That is important because our clinical trial E-5202 in the US assumed that patients with an 18q deletion are at higher risk for tumor recurrence independent of MSI, which may alter the interpretation of the clinical trial.
All these data show that we are learning a tremendous amount about the molecular make up of tumors, but it also shows that it is not easy to develop clinically meaningful markers. However, there is no doubt that new markers will be identified and validated over the years to come and will make our personalized oncology care a reality.