Administration of a CAIX-specific nanobody into mice with DCIS xenografts overexpressing CAIX showed after 2 h a mean tumor-to-normal tissue ratio (TNR) of 4.3 ± 0.6, compared to a TNR of 1.4 ± 0.2 in mice injected with the negative control nanobody R2-IR. Here, CA9 is linked to ductal breast carcinoma in situ.