Is a $950 test that searches for upwards of 50 types of cancer in your bloodstream worth it? That depends on who you ask. Grail, the Silicon Valley healthcare company developing blood tests to pick up early cancer , presented its largest study to date on Saturday at the American Society of Clinical Oncology meeting (ASCO) in Chicago. The study, tracking more than 140,000 older people in the UK, assessed whether people who took Grail's $950 Galleri test each year for three years could catch