A novel technique that particularly “tags” tumors responding to chemotherapy may offer a new strategy for determining a cancer treatment’s effectiveness within days of starting treatment, this is according to a new study done at Vanderbilt-Ingram Cancer Center and was published in Nature Medicine.   This new improved monitoring of tumor response could help customize patient treatment –now the popular term patient-specific care- and also speed up the development of new cancer drugs.   The researchers in the study have identified a small protein that specifically recognizes tumors responding to chemotherapy. The new protein, when tagged with a light-emitting molecule, can be used to visualize cancer response in mice within two days of therapy.  In the present day and age the response to chemotherapy is determined by measuring changes in tumor size with imaging techniques like CT (computed tomography) and MRI (magnetic resonance imaging).  In addition it often takes up to two to three months of cancer therapy before we can determine whether the therapy has been effective for a patient.   If we can get that answer within one to two days, we can switch that patient to an alternative regimen very quickly, and be able to provide the correct treatment to which that particular patient will respond much faster.  Rapid assessment of tumor response is especially important now given recent advances in molecular targeted therapies – chemotherapy medications that specifically interfere with the growth and proliferation of cancer cells while avoiding damage to healthy cells.   There are so many molecular targeted drugs to choose from, and that number is growing every year, so we are now at a point where a patient can be switched from one regimen to another and such new protein tags will be key tools to help make the decision to use an alternative therapy with the patient.  To find a rapid and noninvasive method to assess cancer response to these therapies, the researchers focused not on tumor size, but molecular and cellular changes in responding tumors.   From an array of billions of protein fragments the team identified one that specifically bound to tumors responding to therapy. To this peptide, they attached a light-emitting molecule and injected these labeled peptides into mice that had been implanted with human tumors.  Using specialized imaging methods that detect light in the near-infrared range and saw that tumors responding to therapy were lighting up compared to the non-responding tumors. The peptide detected response in a wide range of tumors – brain, lung, colon, prostate and breast –  all within two days of initiation of treatment.   The next step will be to move the technology into humans. However, the imaging technique used in mice (near-infrared) is not sensitive enough to penetrate deeply into human tissues, so the researchers are adapting the technology to an imaging modality commonly used in humans, called PET (positron emission tomography).   This imaging peptide is predicted to enter clinical trials within about 18 months to see if it is possible to image responding cancers in humans as well as we can in mice.