Editorial Comment to Bone scan index: A new biomarker of bone metastasis in patients with prostate cancer

Abstract

The bone scan index (BSI) was introduced to the clinical setting just a couple of years ago; however, in this short time, the BSI has made a significant impact on the radiographic assessment of bone metastatic lesions in prostate cancer. The fact that BSI has been cited in updated recommendations from the Prostate Cancer Clinical Trials Working Group 3 shows the global acknowledgment of its assessment ability. 1In the previous era, the extent of disease score was used in assessing the amount of bone metastasis, which categorized groups based on the number of metastasis sites of 6 and 20. However, as the range of each score is broad, the detailed assessments are limited. In the case of BSI, the amount (%) of bone metastasis can be calculated by adapting the artificial neural network, which enables the detection of precise baseline metastasis, as well as the range of change among metastatic lesions. 3 The BSI has been adopted in the assessment of bone metastasis among hormone-na€ ıve to hormone-resistant prostate cancer.4,5 The cut-off of the BSI in predicting worse survival varies from 1% to 5%. Uemura et al. reported that a BSI ≥1% predicted survival in metastatic castration-resistant prostate cancer patients, whereas Miyoshi et al. reported a BSI ≥1.9% predicted survival in metastatic castration-sensitive prostate cancer patients. 4,5 Anand et al. reported the change in BSI was useful in predicting survival in castrationresistant prostate cancer patients treated with enzalutamide. 3In terms of a novel approach in radiographic assessment, trans-1-amino-3-18F-fluorocyclobutanecarboxylic acid positron-emission tomography was approved by the US Food and Drug Administration in 2016 as a new diagnostic imaging agent to detect recurrent prostate cancer.6 Furthermore, 68Galabeled prostate-specific membrane antigen positron-emission tomography has emerged to show an advantage over 18 F-choline-based positron-emission tomography in detecting metastatic lesions. 7By combining novel diagnostic tools, we have more options than ever before to evaluate radiographic progression during the course of treatment for prostate cancer. The significance of radiographic assessment is expected to increase in the next couple of years.

State‐of‐the‐art imaging techniques in the management of preoperative staging and re‐staging of prostate cancer

“…BS, however, proves to have a relatively low sensitivity in a per‐lesion analysis because it cannot detect early lesions (which are osteolytic for a short period) and is planar (bone single‐photon emission computed tomography is usually carried out only on positive findings) …”

“…82 BS, however, proves to have a relatively low sensitivity in a per-lesion analysis because it cannot detect early lesions (which are osteolytic for a short period) and is planar (bone single-photon emission computed tomography is usually carried out only on positive findings). 35,83 Nowadays, BS is used in the diagnostic flow chart of PCa patients in many different clinical settings. Thanks to new semiquantitative software, it is also possible to standardize and measure the BS index, which is an imaging biomarker of the extent of whole-body bone metastasis.…”