Others have reported that plasma YKL-40 can be used as a biomarker for monitoring cancer recurrence and prognosis after operation for CRC [21], melanoma stages I and II [34], high grade glioblastomas [14], [35], head and neck cancer after radiotherapy [36], and for metastatic prostate cancer after hormone therapy [37]. The gene discussed is CHI3L1; the disease is head and neck cancer.