Prostate cancer is the second most common cancer in American men and will affect 1 in 8 during their lifetime.1 Management at time of diagnosis depends on the disease stage. If the disease is confined to the prostate, limited surveillance or local treatment of lesions with surgery, brachytherapy, high-intensity focused ultrasound, or radiotherapy may be used.2 Androgen-deprivation therapy will be used in addition to local therapy if the patient has advanced prostate cancer.2 Eventually, many patients will develop resistance to androgen-deprivation therapy or castration-resistant prostate cancer along with metastases and require androgen receptor–targeted therapy or chemotherapy.2 To evaluate these metastatic lesions, positron emission tomography (PET) is used, which can also be used to guide treatment.3 Computed tomography (CT) scans and Tc99m-MDP bone (Tc99) scans were used to develop current therapeutics for patients with castration-resistant prostate cancer.3 More sensitive scans have been developed, including 18F-sodium fluoride (NaF) PET imaging, which has increased bone lesion sensitivity relative to Tc99 scans.3
At the 2021 European Society for Molecular Oncology Congress, Madan and colleagues presented the results of an analysis of serial PET imaging and paired Tc99 scans in 18 patients with castration-resistant prostate cancer who were treated with enzalutamide, an androgen receptor–targeted therapy, with or without prostvac.3 These patients demonstrated no improvement with this therapy. Serial CT, Tc99, and NaF PET scans were used to evaluate the patients. Radiographic progression was found in 14 patients. AIQ technology was used to automatically detect lesions found on NaF PET scans and matched across timepoints.3 The lesions were grouped into 5 categories: completely responding, partially responding, stable disease, progressing disease, or new lesions.
Sixty-seven serial NaF PET scans were evaluated. Although there were 233 completely resolved lesions after treatment start, 52 lesions eventually returned. There were 394 new lesions discovered and 112 of these lesions resolved. In 14 of the 18 patients, new lesions were found that eventually improved. Disease progression occurred in 14 patients, with an average of 11.7 new lesions developing from baseline on the NaF closest to radiographic progression.3 There were 4 patients who had stable Tc99 throughout the study period. These patients had an average of 9.8 new lesions found with serial NaF PET scans.3 Further research is needed to fully understand the clinical significance of the new lesions seen on NaF PET imaging of these patients with stable disease as indicated on Tc99 scans.
