Just like their human owners, many dogs suffer from cancer, which is often malignant, spreading through the body via blood. Once tumors have spread, they usually result in the dog’s death. The tumor cells in circulation (CTCs) can be counted in the blood of people with cancer using immunocapture devices. The number of CTCs in blood can tell us how bad the tumor is, its potential to spread, and how long a person will live for. We have no such way of detecting CTCs in our canine companions. Development of an assay for counting CTCs in canine blood would be of tremendous benefit to our pets because, from a simple blood test, we could detect hidden tumors and get information on tumor severity and the likelihood of spread. Here, we propose to test a novel immunocapture microdevice – the GEDI - for counting tumor cells in dog blood. This device can capture CTCs from blood in human patients with various cancers. We are now going to test to see if it works in the dog. We will take blood samples from healthy dogs, add cultured breast cancer cells to the blood in a test tube, then add the tumor-spiked blood into the GEDI, and count how many added tumor cells are captured. If we find that the GEDI does capture the added tumor cells, we will move forward to see if the device can capture CTCs from the blood of dogs that are known to have cancer.