New Imaging Tool Could Improve Precision in Prostate Cancer Diagnoses

The prostate-specific membrane antigen-targeted positron emission tomography imaging technique will be part of the National Comprehensive Cancer Network guidelines beginning in 2022.

A new imaging technique using prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET) imaging could help locate prostate cancer tumors for more precise treatment, according to a press release.

In addition to identifying cancer lesions in the prostate, the technique could help track cancer that has spread to other parts of the body, which is often missed by current standard-of-care imaging techniques. The tool utilizes PET scanning to identify a radioactive tracer that is highly effective in finding prostate cancer lesions throughout the body, enabling better visualization and more selective treatment.

Researchers at the University of California, Los Angeles and University of California, San Francisco investigated the technique, and according to the press release, their resulting paper led to an FDA approval for the imaging technology. The paper examined the use of the technology for primary staging of prostate cancer before any initial therapy is done.

When patients are diagnosed with prostate cancer and have some pathologic features suggesting risk of metastasis in the lymph nodes or bones, the press release said physicians should know whether the cancer has spread outside of the prostate. PSMA PET/CT scanning is a whole-body imaging modality with high accuracy rates for locating these potential metastases and is the best currently known modality for whole-body prostate cancer staging, according to the paper authors.

In the study, the scan was used in patients at initial staging prior to surgery. The investigators’ primary goal was to evaluate the performance of the scan to detect pelvic lymph node metastasis. The pelvic lymph nodes are commonly the first site of metastasis outside of the prostate, before the cancer has spread to the bone or other organs.

Importantly, the researchers said the only true way to verify whether the cancer is in the pelvic lymph node is to analyze the nodes following surgical removal. They evaluated the ability of the scan to detect some pelvic lymph nodes and identify them as cancerous, compared with the reference gold standard of histopathology analysis.

At the end of the study, only 277 of the 764 patients who received the scan underwent surgery. Approximately 64% of participants underwent another treatment instead of surgery because their scans showed some disease outside of the prostate and the surgeon felt that surgery was no longer ideal. Other treatment options included radiation and hormonal treatments, according to the press release.

Regarding the main goal of the study, the researchers found that the scan had 40% sensitivity, meaning it could detect pelvic lymph node disease in 40% of the patients who actually have pelvic lymph node disease. In 60% of patients, the lesions were still too small to be detected, although the researchers said this is better than any other imaging technique currently available. Furthermore, they noted that the sensitivity would have been much higher if all 764 patients underwent surgery, because most of the patients who did not undergo surgery had large lesions detected by the scan but were not included in the analysis.

In addition to these important findings, the researchers also found very high specificity of the test. When patients did not have pelvic lymph node metastasis, the scan was correctly negative in 95% of cases. Based on this, the investigators said that when the scan finds a positive lesion it is very likely prostate cancer.

According to the press release, the PSMA PET scan is now part of the National Comprehensive Cancer Network (NCCN) guidelines beginning in 2022. The NCCN panel wrote that they “do not feel that conventional imaging is a necessary prerequisite to PSMA-PET. They added that “PSMA-PET can serve as an equally effective, if not more effective, front-line imaging tool for these patients,” according to the press release.

REFERENCE

UCLA Jonsson Comprehensive Cancer Center. Q&A: How a new imaging tool helps to better stage men with prostate cancer. September 16, 2021. Accessed September 23, 2021. https://cancer.ucla.edu/Home/Components/News/News/1740/1631