While it is a popular hobby for many, fishing is also a pastime full of uncertainty. Each time you have something on the line, you can never be completely sure what type of fish you've hooked until you pull it out of the water. In a similar way, scientists "fishing" for biomarkers—molecules whose health care applications include signaling for the presence of cancer—in biofluids such as blood can also encounter unpredictability. Finding a specific protein biomarker in a pool of thousands is like trying to catch a particular fish species in the vast ocean.