Recently, I saw a patient concerned about their family history of colon cancer. As a family physician familiar with genetics, I obtained a thorough family history and discussed the potential for Lynch Syndrome, the most common cause of hereditary colorectal cancer. I recognized the need for better electronic medical record support for documenting a family pedigree, as well as the need for more decision support in recognizing a condition that can be detected early with appropriate screening. Lynch syndrome increases an individual’s risk of developing colorectal cancer by as much as 80%, but with proper care and management, we can reduce this risk and improve their outcomes.
While relieved at a more comprehensive approach to their worries, my patient was still anxious by the prospect of the treatment for cancer. She told me that her brother had a tragic outcome after receiving chemotherapy, which caused severe sores in his mouth, loss of appetite and a fatal gastrointestinal bleed. Based on his diagnosis and treatment history, he likely had a genetic variation that made him more sensitive to fluoropyrimidine chemotherapy, which a simple pharmacogenetic test for DPYD could have detected and avoided.
DPYD mutations result in dihydropyrimidine dehydrogenase deficiency, which affects the metabolism of several important molecules. These include 5-Fluorouracil (5-FU) and its oral prodrug capecitabine, which is used in the treatment of many cancers, including colorectal cancer, breast cancer, and head and neck cancer. Studies have estimated that one in three patients receiving current-generation multi-drug regimens for the adjuvant treatment of colon cancer experienced severe toxicities typically associated with 5-FU.
We have made huge strides recently in the treatment of cancer based on molecular findings. Genetic analysis of tumor cells has emerged as routine testing of many cancers, with tremendous benefits on outcomes of diseases such as non-small cell lung cancer, colorectal cancer, breast cancer, and melanoma, to name a few. More and more biomarkers are available, and we are slowly bringing prevention and early screening to the forefront of treatment methods with the expanded use of genetic testing.
This begs the question: what can be done to accelerate the adoption of pharmacogenetic (PGx) testing in oncology, given its immense potential?
While cost is often cited as an objection, the truth is that the price of a broad pharmacogenetics panel is on par with other routine and frequently repeated chemistry panels. Keep in mind that this test is only done once in a lifetime, hence the mantra “test once, query often.” More importantly, PGx testing gives insight into the proper selection of many other concomitantly used drugs in cancer patients, including pain medicine, anti-nausea drugs, antidepressant treatments, anti-coagulants, proton pump inhibitors, and even Tamoxifen. Clearly, oncology patients deserve the safest and most effective treatments for more than the narrow spectrum of cancer chemotherapy, and by adopting pharmacogenomics testing into standard oncology treatment practice, physicians will be able to support proactive care while maintaining cost efficiency.
While the European Society for Medical Oncology issued a document recommending genetic testing in 2020, the US Food and Drug Administration has yet to mandate DPYD testing for patients receiving chemotherapy. However, other international and American authorities have weighed in on the subject. The Clinical Pharmacogenetics Implementation Consortium (CPIC) has published guidelines for dose reduction of fluoropyrimidines in patients carrying the gene, and the American Society of Clinical Oncology (ASCO) provides a knowledge base for oncologists to have an informed discussion with their patients about the genetic testing for DPYD.
The debate on mandated testing, while essential, unfortunately ignores the more practical need for wider adoption of pharmacogenetic testing. As a family physician involved in counseling cancer patients and their families on the safety and well-being of their comprehensive care, open discussions have reassured them we are doing everything we can to improve both the quantity and quality of their lives. If oncology continues to develop proactive care as a mantra, it will be up to industry leaders and educational programs to continue providing leading-edge information and education to oncologists as well as general, understandable testing and treatment information for oncology patients. By continuing an open discussion on precision medicine and precision care, we can truly accelerate pharmacogenomic testing to its full potential and focus on providing the highest quality care to those who need it most.
Photo: Andy, Getty Images
