Bron101

From other sources (https://www.medscape.com/viewarticle/891491) I was able to find they had a specificity of >99%, with a sensitivity averaging 70% but was as low as 20% on certain cancers (esophageal cancer).

With such an excellent specificity this sounds promising as a cheap screening tool, although the sensitivity is too low in some cancer types to be used as a means to rule out cancer.