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MILAN – Many U.S. patients with gastrointestinal stromal tumors today start on the wrong adjuvant treatment because their physicians don’t order genetic assessment of the cancer, said two American oncologists.
"Initial treatment for GIST [gastrointestinal stromal tumors] is enhanced by molecular decision making," Dr. Jonathan C. Trent said at Sarcoma and GIST 2014, hosted by the European Society for Medical Oncology.
Dr. Jonathan C. Trent
"I’ve had patients referred to me from academic centers where the patient was treated with imatinib [Gleevec], which didn’t work, sunitinib [Sutent], which didn’t work, and regorafenib [Stivarga], which didn’t work. We did genetic testing, and it was a D842V mutation [in the PDGFRA gene]. This patient should never have been treated with these drugs," because GIST that carry this PDGFRA mutation are resistant to all three of these tyrosine kinase inhibitor [TKI] drugs, said Dr. Trent, professor of medicine and director of the bone and soft tissue program at the University of Miami.
"If you’re thinking of giving adjuvant therapy, you absolutely need molecular profiling because in the primary, resected-disease setting, a full 20% of patients will have a mutation that makes imatinib useless, the D842V mutation," said Dr. George D. Demetri, professor of medicine at Harvard University and director of the Center for Sarcoma and Bone Oncology at Dana Farber Cancer Institute, Boston. The potential consequence of not performing a genetic analysis is "you could overtreat 20% of patients with what is a still moderately expensive drug that will give them side effects for 3 years when they don’t need it. That is bad medicine," Dr. Demetri said in an interview. "I’m flabbergasted that more people are not getting molecular profiling for GIST patients being considered for adjuvant therapy. We have not communicated this well. Genetic testing is easily accessible at reference labs."
Dr. Demetri highlighted that identifying a D842V mutation in the PDGFRA gene of a GIST is good news for patients, because when this mutation appears in a primary tumor it flags a very indolent form of GIST. "The physician can tell patients that they don’t need to take this drug because it won’t do them any good, plus most patients with your mutation don’t have their tumor recur for many years and sometimes never."
Dr. George D. Demetri
In its most recent guidelines for GIST management, the National Comprehensive Cancer Network (NCCN) said: "If tyrosine kinase inhibitors are considered as part of the treatment plan, genetic analysis of the tumor should be considered since the presence of mutations (or absence of mutations) in specific regions of the KIT and PDGFRA tyrosine kinase genes are correlated with response (or lack of a response) to specific tyrosine kinase inhibitors."
Similar language exists in the posted GIST management recommendations of the National Cancer Institute (NCI), which date from 2012: "KIT- and PDGFRA-mutational analysis may be of help in predicting responses to kinase inhibitors for patients with unresectable, metastatic, or recurrent GIST who are undergoing therapy with selective TKIs. However, the data are preliminary and mutational analysis for treatment decisions is not routine. There is currently no evidence that basing treatment decisions on mutational analysis improves OS [overall survival]."
Dr. Trent took issue with these positions and said that the NCCN and NCI need to call genetic assessment of primary GIST necessary, especially for patients considered for adjuvant treatment. But others saw reason for equivocation.
Dr. Robert G. Maki
"Since the mutational status of GIST can impact your use of adjuvant therapy or even therapy for metastatic disease, most sarcoma physicians prefer to see it done," noted Dr. Robert G. Maki, professor of medicine and director of the sarcoma program at Mount Sinai Medical Center in New York. "That said, we often do not have clinical trial data to support" this approach to management. For example, no trial results clearly show that GIST that carry a PDGFRA D842V mutation do not respond well to imatinib and have better outcomes when treated with some other drug. "I would like to have these data to discuss the options" with patients, Dr. Maki said in an interview. The relatively well-described patterns of genetic mutation and drug sensitivity seen in GIST make this tumor different from other adult sarcomas, he added.
"We had a patient with the PDGFRA D842V mutation who clearly responded to imatinib," said Dr. Robert S. Benjamin, professor and chairman of sarcoma medical oncology at M.D. Anderson Cancer Center in Houston.
Dr. Robert S. Benjamin
"You use imatinib empirically because it is the most benign drug, especially at the 400-mg/day level," Dr. Benjamin said in an interview. "It’s well tolerated, and it usually works." But Dr. Benjamin acknowledged the added value of learning a tumor’s genetic profile. "It’s analogous to infectious disease," where you might start a patient on an empiric antibiotic but then reconsider once you receive antibiotic-sensitivity results. Genotyping complements the clinical findings made after starting a patient on imatinib, he said.