Cynthia Langwiser is in the fight of her life, battling late stage breast cancer that has spread.
 
"Things have gone very, very well for me. I've had very good results. And you know, I have, you know, essentially my disease is pretty much stable," says Langwiser.
 
Doctors use CT scans to keep track of her therapy, to see if it's working or not.
 
"They always come in and they always tell you what your scan results are immediately because they think, they know, that people have anxiety about that," says Langwiser.
 
She's right. And it can take time for something to show up on an imaging test.
 
"It can take two to three months before we'll see changes. If we'll see something shrink or, worse, if we see something new or growing. And so I'd rather not wait that long," says Breast Oncologist Dr. Minetta Liu.
 
Now Dr. Liu and her patients may not have to. The Georgetown researcher found that a new type of blood test can reliably catch tumor changes sooner.
 
"It's called the CellSearchTM circulating tumor cell test," says Liu.
 
When cancer spreads, tumor cells break free and roam through the blood to a new site. The CellSearch blood test detects and counts those cells, one by one.
 
"So the studies that we've done have linked the number of cells relative to a threshold of five with whether or not a treatment is working and whether patients are doing well or not," says Liu.
 
In other words, if a patient has five or more tumor cells circulating in her blood before treatment, and that number goes down to less than five afterwards, then that treatment's working. Cynthia is a participant in the study and prefers a blood test to scans.
 
"If there was a blood test that was really reliable and the standard of care was such that, you know, you didn't have to have these CT scans, or you know people have to have MRI's so frequently, I think it would be, you know, really good," says Liu.
 
Especially if your number comes up somewhere between zero and four.