The diagnosis of cancer involves the analysis of tissue and cytology specimens obtained through several procedures, including surgical biopsy, endoscopic biopsy, core or aspirational needle biopsy, venipuncture, spinal tap, pleural or ascitic tap, scraping of tissue surfaces and collection of exfoliative cells from urine and sputum. A tumor marker is one which can be used at early stages of the cancer which indicates the likely presence of cancer or that provides information about the likely future behavior of a cancer (e.g. ability to metastasize or to respond to therapy).