Clear cell renal cell carcinoma (CCRCC) is the most common type of kidney cancer. In a study published online on January 31 in the Journal of Clinical Investigation, Niraj Shenoy, MD., M.S., Amit K. Verma, M.B.B.S., and colleagues describe a new prognostic biomarker for this type of cancer called 5-hydroxymethylcytosine (5hmC). As kidney cancer advances, tumor levels of 5hmc progressively decrease. The researchers found that loss of 5hmC occurs because an aberrant metabolic intermediate inhibits enzymes called TET (Ten-eleven Translocation). Furthermore, the presence of ascorbic acid (Vitamin C) prevents the aberrant intermediate from affecting TET and restores 5hmC levels. High-dose intravenous ascorbic acid inhibited kidney cancer growth in a mouse model and increased 5hmc within the tumors. These findings have led to an ongoing multicenter randomized phase 2 clinical trial of vitamin C as an adjunct to standard of care treatment for metastatic and unresectable CCRCC. Dr. Verma is professor of medicine and of developmental and molecular biology at Einstein and attending physician in oncology at Montefiore Einstein Center for Cancer Care. Dr. Shenoy is an assistant professor of medicine at Einstein and attending physician in oncology at Montefiore Einstein Center for Cancer Care.