Furthermore, we show that not all of the genes that are methylated in tumor tissues are also highly methylated in serum cfDNA, as the case for HOXD13 and HOXA11. Although knowledge of the underlying mechanisms involved in determining the levels of these genes in circulating DNA is still limited [46], some evidence suggests that cfDNA is released from tumors as a glyconucleoprotein complex, which might protect it from degradation by nucleases [47]. The gene discussed is HOXD13; the disease is neoplasm.