FDA Approves First Agent for PSMA-PET Imaging in Prostate Cancer

Zosia Chustecka

December 02, 2020

A new radioactive diagnostic agent for use in prostate cancer has been approved by the US Food and Drug Administration (FDA).

The product, Gallium 68 PSMA-11 (Ga 68 PSMA-11), has been approved for institutional use at the University of California, Los Angeles (UCLA) and the University of California, San Francisco (UCSF) under an academic new drug application (NDA).

The FDA approval was based partly on a clinical trial conducted by the UCSF and UCLA research teams on the effectiveness of PSMA PET.

"It is rare for academic institutions to obtain FDA approval of a drug, and this unique collaboration has led to what is one of the first co-approvals of a drug at two institutions," said Thomas Hope, MD, an associate professor at UCSF. "We hope that this first step will lead to a more widespread availability of this imaging test to men with prostate cancer throughout the country."

This approval allows use of PSMA PET only at these two centers. Some other US centers are currently using PSMA as an investigational technique, generally as part of a clinical trial, and they can apply for expedited FDA approval.

The drug itself, Ga 68 PSMA-11, was developed outside the United States by the University of Heidelberg, in Heidelberg, Germany.

A commercial NDA from Telix Pharmaceuticals for TL591-CDx, a radiopharmaceutical cold kit for the preparation of Ga 68 PSMA-11 injection, is under consideration by the FDA.

This is the first drug approved specifically for use in positron-emission tomography (PET) imaging of prostate-specific membrane antigen (PSMA)–positive lesions in men with prostate cancer, the agency noted.

This new imaging approach can "detect whether or not the cancer has spread to other parts of the body," commented Alex Gorovets, MD, acting deputy director of the Office of Specialty Medicine in the FDA's Center for Drug Evaluation and Research

The product is indicated for use in patients with suspected prostate cancer metastasis whose conditions are potentially curable by surgery or radiotherapy, the agency noted. It is also indicated for patients with suspected prostate cancer recurrence, as determined on the basis of elevated serum prostate-specific antigen (PSA) levels.

The FDA notes that two other PET diagnostic agents ― fluciclovine F18 and choline C11 ― are approved for prostate cancer imagining. However, they are only approved for use in patients with suspected cancer recurrence.

Ga 68 PSMA-11 used in PET imaging specifically indicates the presence of PSMA-positive prostate cancer lesions in the tissues of the body.

"PSMA PET/CT is a novel molecular and functional imaging modality specific for prostate cancer cells that has good sensitivity and outstanding specificity in detecting metastasis," commented T. Martin Ma, MD, PhD, of UCLA.

Ma presented a US study on the technique at the recent annual meeting of the American Society for Radiation Oncology. That study showed that PSMA PET/CT led to nodal upstaging in 19.7% of patients and metastasis upstaging in 9.4%.

He said these results were similar to those from the Australian proPSMA trial, which was published in The Lancet earlier this year. That trial found PSMA PET/CT to be superior to conventional imaging with CT and bone scanning for primary staging of high-risk prostate cancer.

"These findings carry significant clinical implications and can affect treatment decision making," Ma commented.

"PSMA PET has been a real game changer in high-risk prostate cancer and has implications in the various stages of prostate cancer management from diagnosis and staging to theranostics," said Renu Eapen, MBBS, of Peter MacCallum Cancer Center, Melbourne, Australia, who was not involved in either study.

"PSMA PET/CT has challenged conventional imaging in staging before curative-intent surgery or radiotherapy," Eapen added.

The accuracy of PSMA PET/CT was 27% higher than that of conventional imaging in the proPSMA trial, she noted in an interview last month. This superior accuracy can ultimately affect management. The imaging has additional benefits of lower radiation dose as well as reproducibility with high reporter agreement, potentially making it a "one-stop-shop" scan.

Clinical Data From Two Trials

The FDA noted that the safety and efficacy of Ga 68 PSMA-11 were evaluated in two prospective clinical trials with a total of 960 men with prostate cancer, each of whom received one injection of the product.

The first trial involved 325 patients with biopsy-proven prostate cancer who underwent PET/CT or PET/MRI scans performed with Ga 68 PSMA-11. "These patients were candidates for surgical removal of the prostate gland and pelvic lymph nodes and were considered at higher risk for metastasis. Among the patients who proceeded to surgery, those with positive readings in the pelvic lymph nodes on Ga 68 PSMA-11 PET had a clinically important rate of metastatic cancer confirmed by surgical pathology," the agency noted.

"The availability of this information prior to treatment is expected to have important implications for patient care," the FDA commented. "For example, it may spare certain patients from undergoing unnecessary surgery.

"The second trial enrolled 635 patients who had rising serum PSA levels after initial prostate surgery or radiotherapy, and thus had biochemical evidence of recurrent prostate cancer. All of these patients received a single Ga 68 PSMA-11 PET/CT scan or PET/MR scan. Based on the scans, 74% of these patients had at least one positive lesion detected by Ga 68 PSMA-11 PET in at least one body region (bone, prostate bed, pelvic lymph node, or extra-pelvic soft tissue). In patients with positive Ga 68 PSMA-11 PET readings who had correlative tissue pathology from biopsies, results from baseline or follow-up imaging by conventional methods, and serial PSA levels available for comparison, local recurrence or metastasis of prostate cancer was confirmed in an estimated 91% of cases," the agency noted.

"Thus, the second trial demonstrated that Ga 68 PSMA-11 PET can detect sites of disease in patients with biochemical evidence of recurrent prostate cancer, thereby providing important information that may impact the approach to therapy," it added.

The FDA also noted that no serious adverse reactions were attributed to Ga 68 PSMA-11. The most common adverse reactions were nausea, diarrhea, and dizziness.

The agency also noted that there is a risk for misdiagnosis because Ga 68 PSMA-11 binding may occur in other types of cancer, and certain nonmalignant processes may lead to errors in interpreting images. In addition, there are radiation risks, because Ga 68 PSMA-11 contributes to a patient's overall long-term cumulative radiation exposure, which is associated with an increased risk for cancer.

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