DISCOVERY IN KIDNEY CANCER
Is a Kidney Tumor Benign? This Not-So-New Test Can Tell
More cases of kidney cancer are being diagnosed now than ever before, in large part due to an increase in the use of cross-sectional imaging techniques such as CT and MRI. But many of these cancers are slow-growing and benign, and may not ever need to be treated, says urologist Michael Gorin, M.D. The problem, he adds, is that "in standard imaging, it's hard to tell whether a tumor is aggressive or not. Some tumors, particularly benign oncocytomas and hybrid oncocytic/chromophobe tumors (HOCTs) are unique in that they are composed of cells with numerous densely-packed mitochondria," the "battery" that makes the cell's energy.
"This test offers the potential of sparing a significant number of patients an unneeded invasive surgical procedure."
In the field of nuclear medicine, radioactive substances that are administered intravenously can be detected on a scan to measure how well or poorly an organ is functioning. One such imaging agent has a difficult name: 99mTc-sestamibi. "It is widely available, often used for heart imaging and to show parathyroid adenomas." 99mTc-sestamibi targets the mitochondria, and clearly shows mitochondria-packed tumors.
Gorin, Mohamad Allaf, M.D., Phillip Pierorazio, M.D. and colleagues recently found 99mTc-sestamibi to be effective in diagnosing oncocytomas and HOCTs. Their preliminary study of six patients was published in Clinical Nuclear Medicine. In a follow-up study, 50 patients who had a newly diagnosed renal tumor were imaged prior to surgery. "This allowed us to compare the results of the imaging test to the gold standard of surgical pathology," says Gorin. In this study, eight of 50 patients were diagnosed with either oncocytoma or HOCT at the time of surgery. 99mTc-sestamibi and SPECT/CT imaging correctly identified five of six oncocytomas and two out of two HOCTs, resulting in an overall sensitivity of nearly 88 percent. "Using this technology, we can be very certain that patients with a "hot" tumor have a benign mass," states Allaf. In addition, only two tumors were falsely positive on the imaging test.
"Based on these findings, 99mTc-sestamibi SPECT/CT appears to be an excellent test for the preoperative identification of benign renal tumors and offers the potential of sparing a significant number of patients an unneeded invasive surgical procedure," says Pierorazio. The investigators plan on confirming this with a larger study. Besides Gorin, Allaf, and Pierorazio, authors included Mark Ball, Christian Pavlovich Jonathan Epstein and Alex Baras.