BRUSSELS – Researchers developing advanced imaging techniques for breast cancer patients are striving to move beyond merely documenting the size and shape of tumors to also generate information on a tumor’s physiologic characteristics and molecular composition. But these goals remain investigational, leaving the proven role of advanced imaging techniques somewhat limited.
Work is underway trying to combine the structural information obtained from MRI with metabolic imaging using a glucose tracer and positron emission tomography (PET). Investigators are also trying to expand the capabilities of PET and single-photon emission computed tomography (SPECT) with new labeled tracers that can help visualize estrogen receptors, androgen receptors, and HER2 receptors.
But even the most basic PET and SPECT analyses available today require more supporting data before they can enter routine practice. "We have to prove that it affects clinical decision making and is useful," said Dr. Elisabeth de Vries, during an imaging session at the IMPAKT 2013 Breast Cancer Conference.
Currently, the development of imaging modalities for assessing breast cancer drug targets like HER2 and estrogen receptors is "still in its infancy," said Dr. de Vries, professor and head of the department of medical oncology at the University of Groningen, the Netherlands.
The potential exists to use PET and SPECT to find and assess tumor metastases throughout a patient’s body, and to gain insight into receptor heterogeneity with a new tracer for each important breast cancer marker, but these methods still need refinement and documentation of utility, she said.
Dr. Katja Pinker-Domenig believes that the best imaging information to guide breast cancer management will come from combining information from multiple sources, such as MRI and PET or MRI and SPECT, and her group has begun to assess these couplings. Last December, they reported their experience using 3-Tesla MRI and labeled glucose in PET imaging to assess 60 patients with lesions initially detected by mammography or ultrasound and classified as categories 3-5 on the Breast Imaging Reporting and Data System (BI-RADS).
Combining the two methods resulted in a diagnostic sensitivity of 100%, a specificity of 91%, and a diagnostic accuracy of 97%, significantly better than the 97%/77%/90% rates obtained in the same patients using MRI alone, they reported at the annual meeting of the Radiological Society of North America (RSNA). Adding the metabolic PET assessment to MRI produced two false positives and unnecessary biopsies, compared with five false positives and unneeded biopsies that would have been done based on MRI only, said Dr. Pinker-Domenig, a radiologist at the Medical University of Vienna.
Another MRI enhancement she is working on adds information from MRI diffusion-weighted imaging, which can distinguish benign cells, which freely diffuse and have a high apparent diffusion coefficient, and malignant cells, which have much more restricted diffusion. In another report at the RSNA last December, Dr. Pinker-Domenig and her associates presented results from 233 patients with 279 suspicious breast lesions examined by diffusion-weighted imaging using a 3-Tesla magnetic field. Overall sensitivity was 92% and specificity was 90% compared with subsequent biopsy and histopathology.
"With diffusion-weighted imaging we can often see changes before they are visible with contrast-enhanced MRI. We can even see malignancies disappear during chemotherapy. What is thrilling about DWI is that we can see changes before we can pick them up with conventional imaging with contrast-enhanced MRI," she said.
Another way of dealing with the limitations of conventional, stand-alone MRI has been to move to higher magnetic field strengths, at 3 or 7 Tesla. Last year, Dr. Pinker-Domenig and her associates reported results using 3-Tesla MRI on 150 breast cancer patients with 99% sensitivity, 81% specificity, and a diagnostic accuracy of 93% (Eur. Radiol. 2012;22:322-30), results she called "pretty good but not sufficient." In February, the group reported at the annual meeting of the European Society of Radiology their initial experience in 25 patients using 7-Tesla MRI to image breast cancers. The boost in field strength produced only a modest uptick in sensitivity and diagnostic accuracy, but Dr. Pinker-Domenig maintained the extra cost was worth it because "the pictures are clearer," and they also likely provide more information on tumor heterogeneity, she said.
In contrast to these advances, using imaging to assess bone metastases in breast cancer patients has made little progress. "We’re not very good at looking at bone metastases with bone scans, x-rays, or PET," said Dr. Gary Cook, a radiologist at King’s College, London. These imaging modalities allow radiologists to see gross changes, but not in the detail needed for reproducible measurements. "There is a lack of sensitive, specific, reproducible, and quantifiable methods to monitor bone metastases," he said.