Cyotgen (Princeton, New Jersey) has reported the publication of a seven-year survival study that suggests its molecular imaging agent, Prostascint, may help predict which patients are less likely to benefit from brachytherapy for prostate cancer.

The company said that Prostascint is the “first and only” commercial monoclonal antibody-based agent that targets prostate-specific membrane antigen (PSMA) to image the extent and spread of prostate cancer. PSMA is expressed in prostate cancer cells, with increased expression in high-grade cancers, metastatic disease and hormone-refractory prostate cancer.

The study evaluated the use of Prostascint fusion imaging to define brachytherapy treatment regimens for 239 newly diagnosed prostate cancer patients.

“[Fusion imaging] is a process whereby you combine two separate imaging techniques to form a single fused image,” Cytogen CEO Michael Becker told Diagnostics & Imaging Week.

According to Becker, an imaging technique like CT or MRI provides “exquisite anatomical information” however, what it does not provide — that is available through other imaging techniques like SPECT — is “functional information, in other words, where the cancer cells are, [and] where the disease has progressed to,” which is something that imaging with an agent like Prostascint or PET imaging can provide.

Fusing the two types of images — anatomical and functional — really provides “the best of both worlds,” Becker said.

Prostascint is a “nuclear medicine-based imaging agent” and consists of Cytogen’s PSMA-targeting monoclonal antibody, 7E11-C5, linked to the imaging radioisotope Indium-111. Cytogen said that by targeting PSMA, the Prostascint molecular imaging procedure can detect the extent and spread of cancer by using a standard gamma camera.

The recently published study on Prostascint appears in the online edition of the American Brachytherapy Society’s (Reston, Virginia) peer-reviewed journal Brachytherapy.

The study evaluated the use of Prostascint’s fusion imaging to define brachytherapy treatment regimens for 239 newly diagnosed prostate cancer patients. Prostascint fusion imaging was used to assess local and distant disease and to alter the radiation dose to areas of suspected high tumor burden.

Prostascint was found to significantly and independently predict biochemical disease-free survival. Using the American Society for Therapeutic Radiation and Oncology (ASTRO; Fairfax, Virginia) standard criteria to monitor PSA response for reporting disease-free survival, the cure rate was 90.6% for patients whose fused Prostascint scan showed local disease vs. 66.1% for patients with distant disease.

Becker said that because prostate cancer is a relatively slow-growing cancer, companies need “a longer time period to kind of dissect or distinguish trends in prostate cancer studies.”

“The continued improvement in this type of imaging technology has now led to a refinement in treatment planning based on the fused images,” said Rodney Ellis, MD, a radiation oncologist and assistant professor of urology with the Case School of Medicine of Case Western Reserve University (Cleveland) and the lead author of the publication. “These data suggest that Prostascint fusion imaging is emerging as an important tool to help determine patient-specific treatment regimens for prostate cancer patients.”

Becker told D&IW that in its initial years of launch following its FDA approval in 1996, Prostascint “was somewhat discounted in terms of its ability to add value for the patient or the physician.” One problem was that the technology available only offered “very low resolution and somewhat . . . difficult-to-interpret images.”

Now, he said, not only has technology advanced, but also studies such as the one just published “illustrate the attributes for Prostascint for prostate cancer patients.”

Prostascint is FDA-approved for two separate groups of patients: newly diagnosed, high-risk patients; and patients with recurrent disease.

In the current study, the researchers used Prostascint in an off-label capacity, or one for which the FDA has not given its approval. Instead, researchers used the Prostascint-enabled image to determine where to implant seeds in the prostate. It allowed the physician to use fewer seeds in areas of the prostate where there was less cancer, and to place more seeds in areas where there was more cancer, Becker said, thereby allowing him to “minimize the toxicity” and “increase the efficacy.” And although it is not approved for this use, physicians can do so.

“It’s certainly not [uncommon] in the oncology landscape to have not only diagnostics but therapeutics used in off-label indications,” Becker said.

Prostate cancer is the most common type of cancer found in men in the U.S., other than skin cancer. The American Cancer Society (Atlanta) estimates there will be about 218,890 new cases of prostate cancer in the U.S. in 2007, and about 27,050 men will die of the disease.