If you were tuned to CNN on May 11th to watch HHS Secretary Tommy Thompson announce the approval of anti-cancer drug Gleevec, for treating a type of leukemia and a rare stomach tumor, you realize we’re at the dawn of a new era.
The excitement around Gleevec comes down to its standing as the first of a new kind of drug that is designed to kill only cancerous cells while generally sparing healthy ones. This first “molecularly targeted drug” is the fruit of three decades of research into the molecular biology of cancer, which gives this event importance that stretches far beyond the relatively small number of patients who stand to benefit from it immediately.
Drug approvals never gain such fan fare, but this announcement did, drawing Thompson, Richard Klauser, M.D., the director of the National Cancer Institute and Daniel Vasella, M.D., the chairman and CEO of the drug’s developer Novartis.
So what does this have to do with medical imaging?
A lot. This month we’re focusing on nuclear medicine (starting on page 26), and more specifically on the ability of PET and combined PET-CT scanners to allow physicians to “look” deep inside the body to diagnose and monitor cancer. The future of PET-CT in hybrid and fusion imaging will allow us to image beyond tumors to the molecules inside (via diagnostic compounds that bind to molecular targets) to find the precursors of disease. The hope is that this will eventually enable physicians to change the course of disease management by spotting disease even before traditional symptoms appear. We’re still at least five to 10 years off, but the first steps have been made.
Look at chronic myelogeneous leukemia or C.M.L., the type of leukemia Gleevec now targets. C.M.L., unlike most types of cancer that start when the tumor has accumulated many different genetic defects, starts with the swap of sections of DNA between two chromosomes, 9 and 22. In the swap, chromosome 22 loses a vital section that enables the signaling protein to shut itself off. The constant signaling of the defective protein is presumed to be what causes white blood cells to keep dividing. Gleevec works by jamming the protein in the off position, thus stopping the division of cancerous white blood cells.
Some day, imaging may enable physicians to predict those at risk of C.M.L. by examining their chromosomes — and cure the problem via pharmaceutical-based gene therapy (perhaps even personalize) before symptoms manifest themselves.
Tests of similar drugs are proving useful in blocking tumor growth by inhibiting certain proteins, although not killing the tumors altogether. Researchers thus see a transitionary period for cancer in its becoming a chronic disease like diabetes, with patients remaining alive for years even though the tumors are not gone. The next step would be eradication.
In the meantime, PET and SPECT are flourishing, with PET reimbursement blossoming and hard-core lobbying for more indications continuing. Research is finding more effective radiopharmaceuticals to increase the specificity of PET for targeting cancer as well as neurological and cardiovascular diseases. And perhaps most importantly, the proliferation of PET systems (the installed base of 200 is doubling annually), including mobile units, allows more physicians to use the technology and push the envelope of clinical knowledge and applications.
According to Thompson, the targeted approach to cancer treatment and rapid FDA approvals are “the wave of the future.” Imaging is sure to ride the wave.
Mary C. Tierney, Editor
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