BACKGROUND: Patients with certain types of tumors, in particular brain tumors, will frequently rely on radiologic imaging, such as magnetic resonance imaging (MRI), for diagnosis and treatment monitoring. Unfortunately, MRI and similar modalities are often subject to interpretation and can be highly subjective in nature, making it difficult to differentiate between actual tumor recurrence and treatment effect. Subsequent or alternate methodology involving biopsy or other surgical procedures, can be highly invasive, dangerous, and lead to an extensive recovery time in patients undergoing such procedures. A less invasive method to reliably identify tumor recurrence would be valuable to clinicians and their patients during evaluations following treatment and/or surgical resection of a tumor. TECHNOLOGY: UCSF inventors have discovered a novel cancer biomarker that is expressed on the surfaces of myeloid cells, so that tumors can be evaluated for recurrence by screening small amounts of peripheral blood in patients. So far, these findings have been done in glioblastoma and prostate cancer patients, but further studies are underway for other types of solid tumors.