YKL-40, also known as chitinase-3-like 1 (CHI3L1) or human cartilage glycoprotein-39, is a 40 kDa secreted glycoprotein with two potential N-linked glycosylation sites which has been proposed as a biomarker in a variety of cancers but has not received FDA approval [132]. Here, CHI3L1 is linked to cancer.