• Researchers from the University of California Davis (Sacramento, CA) presented the first patient scans from a custom-built breast PET/CT system. According to Ramsey Badawi, assistant professor of radiology at UC Davis, the technology enables physicians to "get much more accurate images of tumours - especially small tumours - than conventional full-body PET scans". As well as determining the stage of the cancer and the appropriate treatment, breast PET/CT could eventually be used for early detection of a drug's effectiveness in individual patients, and for studying new drugs and imaging agents.
The PET camera consists of two adjustable planar heads made up of pixelated LSO crystal arrays. Patients lie prone while the PET and CT systems rotate around the freely suspended breast. Initial patient scans indicated that PET and CT images of the uncompressed breast are accurate and provide clinically relevant data (scientific paper 97).
• Molecular Insight Pharmaceuticals (Cambridge, MA) described two new molecular imaging radiopharmaceuticals that demonstrate promising prostate-tumour targeting profiles. Working in collaboration with Johns Hopkins Medical Institutions (Baltimore, MD), the biopharmaceutical company developed radio-iodinated small molecules that bind specifically to prostate-specific membrane antigen (PSMA). PSMA is expressed at high levels in almost all prostate cancers, including metastatic disease, and its expression correlates with tumour stage, progression and disease recurrence.
According to the researchers, molecular targeting with small molecules may provide more effective diagnosis and monitoring of prostate cancer than current radiolabelled anti-PSMA antibodies, due to their potential for high tumour uptake and rapid normal-tissue clearance (scientific paper 389).
• A research team headed up at the Radboud University Nijmegen Medical Center in the Netherlands has proposed a radioimmunoimaging scheme based on a two-step approach to radioisotope delivery. This so-called pre-targeting involves injection of a bispecific monoclonal antibody (bsMAb), which recognizes both a tumour-associated antigen and a peptide-conjugated imaging agent. Once the bsMAb has accumulated in the tumour, the imaging agent is given, which then targets this localized bsMAb.
Pre-targeting in human colon cancer cells transplanted in mice resulted in high tumour-to-blood and tumour-to-kidney ratios of radioisotope uptake. The scheme thus offers an attractive alternative to traditional radioimmunoimaging, in which radioisotopes are delivered to the tumour linked to antibodies (which exhibit slow blood clearance). The researchers note that bsMAb pre-targeting has applications beyond molecular imaging, and could also be used to improve the selective delivery of therapeutic isotopes and cytotoxic drugs to cancers (scientific paper 209).
• PET imaging with the radiotracer Pittsburgh Compound B (PiB) shows promise for early detection and progression monitoring of Alzheimer's disease (AD). PiB binds to the beta-amyloid plaques found in the brains of patients with AD, and thought to be responsible for the onset of the disease. Researchers at the University of Pittsburgh (Pittsburgh, PA) scanned 35 patients: four with AD, 10 with mild cognitive impairment (MCI) and 21 elderly controls. They hypothesized that that MCI subjects with brain plaque would develop AD and those without would not advance to AD.
About 60% of MCI subjects had plaque loads comparable to AD subjects, while about 35% had no detectable plaque. After monitoring the participants for four years, the researchers found that only those with plaque progressed on to a clinical diagnosis of AD. They note that about 25% of the control group also had significant deposits of plaque in their brains and suggest that these subjects are in a pre-symptomatic, at-risk state that will eventually lead to AD (scientific paper 139).