A test that measures the amounts of two members of the same protein family - one of which appears to act as an oncogene, and the other as a tumor suppressor - helps identify patients with breast cancer who will likely benefit from chemotherapy and those who won't, according to researchers.
The test, known as OncoPlanTM, is already commercially available, and studies have shown that it can predict the aggressiveness of the patient's tumor and the relative risk of disease recurrence following surgery in breast, colon and gastric cancers. Now, researchers in the U.S. and Canada have studied whether it also can help identify breast cancer patients who would benefit most from chemotherapy.
Results were presented at the first meeting on Molecular Diagnostics in Cancer Therapeutic Development, organized by the American Association for Cancer Research.
OncoPlan measures two forms of Shc protein, which are known to drive the formation of protein complexes involved in signal transduction pathways and have been found to be involved in many of the pathways important to development of aggressive cancer. These two forms have a "push pull" relationship with each other: tyrosine-phosphorylated (PY)-Shc helps drive these dangerous cell pathways, but p66 Shc, after initial stimulation, works to inhibit the very growth pathway the other Shc proteins promote.
"This may be one mechanism whereby normal cells prevent runaway growth," said the study's lead author, A. Raymond Frackelton, Jr., Ph.D., a Brown University associate professor, staff scientist at Roger Williams Medical Center and Vice President of Research at Catalyst Oncology, which is marketing OncoPlan. "Perhaps more importantly, aggressive cancer cells must endure oxidative stress--stress that in normal cells triggers p66 Shc to cause cellular suicide," he said. "Tumor cells, then, may have both growth and survival advantages if p66 Shc levels are low."
Chemotherapy-mediated killing of tumor cells, however, does not require p66 Shc, Frackelton said, suggesting that patients whose tumor cells have low p66 Shc might respond well to chemotherapy. To test this idea, the researchers looked at the Shc proteins in tumors from 2,380 women from British Columbia who were diagnosed with invasive breast cancer, 717 of whom received chemotherapy as part of their initial treatment.
They found that, indeed, patients who had low levels of p66 Shc and did not receive chemotherapy had very poor outcomes. If similar patients received chemotherapy, however, their chances of relapsing and dying from their disease were reduced by two-fold or more, said Frackelton. Conversely, women with high levels of p66 Shc had a much higher likelihood of surviving their disease, but appeared to derive no benefit from chemotherapy, he said.
Possible additional associations between PY-Shc and chemotherapy benefit has not yet been fully explored, Frackelton said. "But even at this point, the results are very exciting because, with further validation in clinical trials, OncoPlan, which is already being used to predict disease aggressiveness, will help to ensure that individual patients receive the most beneficial therapies," he said.
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