Despite the missing proof that progress as assessed by bone scintigraphy is correct, Imbriaco et al. introduced a method of measuring metastatic bone involvement in bone scintigraphy of prostate cancer—the so-called bone scan index (BSI) [24]—and could show that it features a high correlation with prostate-specific antigen (PSA) and low intra- and inter-observer variability. The gene discussed is KLK3; the disease is prostate cancer.