1. Medical Oncology Department, Ramón y Cajal University Hospital, 28034 Madrid, Spain
2. Ramón y Cajal Health Research Institute (IRYCIS), 28034 Madrid, Spain
3. Gastroenterology Department, Ramón y Cajal University Hospital, 28034 Madrid, Spain
4. Pathology Department, Ramón y Cajal University Hospital, 28034 Madrid, Spain
5. Biomedical Research Network in Cancer (CIBERONC), 28029 Madrid, Spain