Combining conventional imaging, noninvasive imaging test improves kidney tumor classification

Johns Hopkins University researchers found in a recent study that adding 99mTc-sestamibi SPECT/CT, a noninvasive imaging test, to CT or MRI increases accuracy in classifying kidney tumor. This potential improvement in diagnostic accuracy could reduce unnecessary surgery.

The study, published in Clinical Nuclear Medicine, details the researchers work to improve kidney tumor classification. The team reports that the sestamibi SPECT/CT test adds extra diagnostic information in conjunction with CT and MRI and improves physicians’ ability to differentiate between benign and malignant kidney tumors.

"Sestamibi SPECT/CT lets radiologists and urologists 'see' the most common benign kidney tumor, something CT and MRI have not succeeded in doing alone," said Mohamad E. Allaf, MD, MEA Endowed Professor of Urology at Johns Hopkins, in a statement. "This noninvasive scan may prevent patients with a potentially benign kidney tumor from having to undergo a surgery to remove the tumor or potentially the entire kidney, along with its associated risks and high costs. At Johns Hopkins, use of this test has already spared a number of our patients from unnecessary surgery and unnecessary removal of a kidney that would require them to be on dialysis. These results are hugely encouraging, but we need to do more studies."

As part of the study, 48 participants who were diagnosed with a kidney tumor on conventional CT or MRI were imaged with sestamibi SPECT/CT prior to surgery. Radiologists graded the conventional and sestamibi SPECT/CT images benign or malignant using a five-point scale (1= definitely benign, 5=definitely cancerous). Radiologists were also asked not to talk amongst each other on their findings.

After patients underwent surgery, similarly “blinded” pathologists assessed the tumors without knowing any of the radiologists findings and found that eight of the 48 were benign. The other 40 were classified as a variety of other tumor types, including malignant renal cell carcinomas.

Taking a look at sestamibi SPECT/CT scan results in conjunction with CT or MRI altered the initial rating levels from cancerous toward benign in nine cases and changed reviewers’ score from likely cancerous to definitely cancerous in five cases. This conjunction also increased the reviewers’ diagnostic certainty in 14 of the 48 patients.

The investigators were able to identify seven of the nine benign tumors by adding sestamibi SPECT/CT and noted that this addition to conventional imaging outperformed conventional imaging alone. On this measure, a value of 0.50 indicates that a diagnostic test is no better than chance. Conventional imaging combined with sestamibi SPECT/CT had a value of 0.85, while conventional imaging by itself had a value of 0.60.

The researchers also noted the addition of sestamibi SPECT/CT increased physicians’ confidence in being able to classify malignant tumors, which in turn decreases the risk of misdiagnosis and unnecessary surgeries.

"As radiologists, we have struggled to find noninvasive ways to better classify patients and spare unnecessary surgery, but this has not been easy," says Steven P. Rowe, MD, PhD, one of the two former residents who developed this approach, and now assistant professor of radiology and radiological science at the Johns Hopkins University School of Medicine. "Sestamibi SPECT/CT offers an inexpensive and widely available means of better characterizing kidney tumors, and the identical test is now being performed as part of a large trial in Sweden, for which the first results have just recently been published and appear to confirm our conclusions."

Researchers will need to further evaluate this approach to establish its validity, but as of now, Michael A. Gorin, MD, the other resident involved in developing this approach, said this test appears to be a less expensive, faster, noninvasive alternative to surgery.

"In the absence of diagnostic certainty, surgeons tend to remove kidney tumors in an abundance of caution, leading to an estimated 5,600 surgically removed benign kidney tumors each year in the United States," he said.