HJBR Mar/Apr 2023

58 MAR / APR 2023 I  HEALTHCARE JOURNAL OF BATON ROUGE ONCOLOGY DIAL GUE COLUMN ONCOLOGY What is precision oncology? For much of the history of medical oncolo- gy, treatment has relied on cytotoxic chemo- therapies that non-selectively target rapidly dividing cells. Because of their indiscriminate modes of action, these regimens have gen- erally had a suboptimal side effect profile, including hair loss, diarrhea, reduced blood counts, and other varied organ dysfunctions. Furthermore, these conventional approaches have been ineffective in some tumor types, especially in more indolent cancers. With ris- ing interest in personalizedmedicine, broadly speaking, medical oncologists have been ea- ger to embrace more precise approaches to enhance both the efficacy and safety profile of cancer treatments. Precision oncology revolves around the concepts of biomarkers and targeted therapies. Biomarkers aremolecular features that help to subclassify tumors beyond their base histol- ogy and can be prognostic or predictive . Prog- nostic biomarkers forecast the likely behavior of tumors and help determine whether they present a high or low risk of disease progres- sion and death. Predictive biomarkers predict the response or non-response of tumors to specific treatments, especially targeted thera- pies that have a selectivemechanismof action in contrast to themore indiscriminate behav- ior of conventional cytotoxic chemotherapies. Notably, the distinction between prognos- tic and predictive biomarkers often comes down to the availability of efficacious tar- geted therapies. For instance, pathognomon- ic BCR-ABL gene translocations in chronic myelogenous leukemia (CML) were once a prognostic biomarker that portended a ter- rible prognosis. However, with the advent of imatinib and other tyrosine kinase inhibitors (TKIs) targeting this fusion protein, this is now a predictive biomarker. With proper intervention, these patients can now have a nearly normal lifespan. Thus, there is hope that the prognostic biomarkers of today can become the predictive biomarkers of tomorrow. How has precision oncology changed practice thus far? Recent history is replete with examples of the successful implementation of precision oncology. Aside from the example of BCR- ABLTKIs in CML, perhaps the most apparent example of this is the use of biomarkers to subcategorize breast cancers by endocrine receptor and HER2 expression to best assign therapy. Rituximab and other CD20-directed therapies have dramatically improved out- comes in CD20-positive B cell lymphomas. In HITTING THE TARGET: Precision Comes to Medical Oncology