to the public. nbc's erica edwards has more. >> reporter: even when surgery, chemotherapy and radiation effectively cure cancer patients, survivors often have lingering questions. >> is someone truly cured or are there a few cells five to ten laters might come back and start to grow. >> reporter: this doctor is a lung cancer expert. he's one of many around the country scheduled to begin clinical trials on a blood test predicted to detect a single cancer cell still circulating in the body after treatment. >> you don't see a tumor on a cat scan, a ct scan, until it's grown a certain size. so this could be potentially more sensitive than imaging. >> reporter: if the test proves to be successful doctors say it has the potential to replace painful biopsies used now to check for cancer cells that have spread. it could also give doctors an early head's up on whether a treatment is working and a better understanding of what's