Compared to our previously published peptide [18F]414 (Pra(6-[18F]FGlc)-NLys8-Lys9-Pro10-Tyr11-Tle12-Leu13, Fig. 1A), the tumor uptake of [18F]21 was 3–fivefold higher (5%ID/g) and [18F]21 revealed improved tumor retention at 60 to 90 min p.i. (2.1–2.6%ID/g). The gene discussed is S100A6; the disease is neoplasm.