Imaging - June 2021

This issue is focused on the PSMA scan, which represents a major advance in prostate cancer imaging. This technique allows us to image prostate cancer metastases to bone and other sites down to 2-4 mm, far below the threshold of the commonly used CT and MRI scan.

 The PSMA scan looks to improve the management of prostate cancer at several points in the natural history of this cancer. In men with newly diagnosed prostate cancer, this scan will improve our ability to identify men with early metastatic disease. These men are likely to recur after radical prostatectomy and can better be treated by approaches that take into consideration the extent of their disease.

 In patients with metastatic disease, this scan is much better than the CT and bone scan in identifying the sites of metastatic disease. This will likely improve our ability to identify oligometastatic disease as well as direct radiation therapy in this setting. It is also likely to do a better job documenting response to systemic treatment as well as progression.

 It is important to recognize that this scan has certain limitations. While this scan is quite sensitive, it does have a lower limit of 2-4 mm in the size of the metastases it can visualize. Additionally, there are prostate cancers that produce little or no PSMA and are thus not identified by this scan. Some metastatic lesions have been shown to have areas that are PSMA negative and areas that are positive. Thus treatment targeted at PSMA positive cancer might foster the emergence of PSMA negative cancer.

 Charles E. Myers, Jr., MD

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