Pinpointing prostate problems without surgery

Magnetic resonance spectroscopy, the molecular cousin of MRI could be used to pinpoint the exact location of prostate cancers and to determine the aggressiveness of a tumour, according to research published in the Science Translational Medicine. The approach could help guide treatment.

Prostate cancer is one of the most prevalent forms of cancer in men and can be lethal if left untreated. However, precise diagnosis is difficult, metastases are common in the lethal forms, and successful excision relies on being able to obtain detailed images of the spread of the tumour. Magnetic resonance (MR) spectroscopy which can analyse the biochemistry rather than the physical structure of tissues could give oncologists a better way to home in on prostate cancers at the early stages of growth and so ultimately improve treatment success rates.

"Based on prostate cancer statistics that the majority of prostate cancer detected from PSA tests are not lethal, but the current pathology cannot differentiate them from lethal ones, thus the biggest issue is over treatment, but the current report does not yet have the ability to address this, it could address another important issue ie untargeted biopsy with targets," Leo Cheng told spectroscopyNOW.

Prostate-specific antigen (PSA) screening is the standard for detecing prostate disease but does not, unfortunately, distinguish between benign and malignant growth, making a surgical biopsy a necessity for detecting cancer. But, prostate tumours may be confined to only a small portion of the prostate, which means even a surgical assessment can easily fail to detect the presence of malignant tissue.

Chin-Lee Wu of the Department of Pathology, at Massachusetts General Hospital (MGH), Harvard Medical School, Boston, MA, and colleagues explain the problem further: "As current radiological approaches cannot accurately localize prostate cancer in vivo, biopsies are conducted at random within prostates for patients at risk for prostate cancer, leading to high false-negative rates." They point out that, "Metabolomic imaging can map cancer-specific biomolecular profile values onto anatomical structures to direct biopsy."

The current work builds on a 2005 study by Cheng and colleagues in which they demonstrated that metabolomic profiles constructed from MR spectroscopy could distinguish between malignant and benign tissue from the prostate. The technique emerging from that study was superior, the team said, to traditional pathology in forming a prognosis for the patient.

They have now carried out a preliminary study by evaluating five whole prostates, rather than samples, removed during prostatectomy from cancer patients who had biopsy-proven cancer. They obtained localized, multi-cross-sectional, multivoxel magnetic resonance spectra were then used to construct a profile of the malignancy of the prostates. "We generated profiles for the 7T data according to the 14T profile structure, and tested how close the resulting profile in comparison with pathology to the metabolomic profiles we had obtained in the 2005 study using a high-power, 14 Tesla, NMR spectrometer," Cheng adds.

The researchers have now correlated their malignancy index with lesion size and were able to obtain an accuracy of 93 to 97% in detecting cancerous tissues compared with the conventional non-spectroscopic diagnostic techniques.

"Collectively analyzing all the metabolites measurable with a 7-Tesla MR scanner maps out prostate cancer in a way that cannot be achieved by any other current radiological test or by analysing changes in a single metabolite," explains senior author Leo Cheng of the MGH Imaging and Pathology departments. "It detects tumours that cannot be found with other imaging approaches and may give us information that can help determine the best course of treatment."

Cheng explains that the metabolic profile of a prostate tumour could be a very powerful technique. "As we analyse more and more tumours with spectroscopy, we should be able to define profiles that reflect specific clinical and pathological states, achieving a true needle-free, MR biopsy," he explains. "And once these spectra are measured, they can be recombined to provide profiles reflecting parameters from the tumour's location to, ultimately, its aggressiveness."

The aim of the research is to facilitate MR spectroscopy as a diagnostic technique, without having to surgically remove the prostate, and the use of the whole-body scanner for the MR spectroscopy should make this possible. Tests to confirm that 3 T machines would be adequate are also planned.

The removal of the prostate is a major surgical intervention and does not have the most positive outcome for patients in terms of quality of life, although it does save lives, of course.

The team hopes to move into clinical trials within a year or two. "As long as we can define appropriate metabolomic profiles, this concept could someday be used for any kind of tumour or medical condition," adds Cheng. Eventually we hope to move the field of radiology from analyzing images that show the effects of disease to producing images that reveal the disease process itself."

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.