The increase of targeted therapies in oncology practice highlights the opportunity to individualize cancer therapy through biomarker testing. Two patients with the same diagnosis can respond very differently to treatment because multiple factors influence their prognosis, treatment, and outcomes. Kristin Daly, MSN, ANP-BC, AOCNP®, a nurse practitioner from the Siteman Cancer Center in St. Louis, spoke at the 2022 ONS Bridge Conference about how biomarkers can help to identify who may benefit from targeted therapy and how identified variants can be used to determine cancer treatment.
Biomarkers Versus Tumor Markers
Terminology can be confusing to professionals and patients alike. Basically, biomarkers and tumor markers both provide data.
- Biomarker: Short for biological markers, a biomarker is a measurement that captures key information at that specific time. A biomarker is a “gene, protein, or other substance we can test for, specific to a patient’s cancer, which provides information that helps us design and refine a patient’s treatment and/or surveillance so that it is more effective and targeted,” stated Ms. Daly. She shared that oncology nurses are probably already familiar with biomarkers and their use in clinical practice (eg, HER2, ER/PR, CEA, p16, RET, EGFR, and BRCA1). Many more biomarkers than these exist, but testing for them is not yet available. Conversely, some biomarker testings are available but do not have actional targets, meaning no drug approvals exist against that specific target. Knowing these biomarkers help providers understand which patients may benefit from treatment and how to treat the cancer effectively.
- Tumor marker: Testing for tumor markers is another method to determine whether a patient is a candidate for a particular targeted therapy. A tumor marker is anything present in or produced by cancer cells or other cells in response to cancer. Although some tumor markers are associated with only one type of cancer (eg, CA-125 in ovarian cancer), others are related to multiple cancer types. “All tumor markers are biomarkers,” Ms. Daly explained, “but not all biomarkers are tumor markers.”
Germline Versus Somatic Variants
Biomarkers can be categorized as germline or somatic variants. Germline variants—changes that are inherited and can be passed on to children—occur only in 5-10% of cancers. Germline variant testing uses blood or a swab from the cheek. “While having this variant increases the risk of developing a cancer, there is not 100% penetrance, meaning not all persons with variants will get it,” said Ms. Daly.
Somatic variants are more common than germline variants. Somatic variants are not inherited or passed on to children but instead occur in the cells of a person’s body after conception. Somatic variant testing uses tumor tissue or liquid biopsy/circulating tumor DNA, making up most of the biomarker testing seen in cancer care. Somatic variants can be positive, negative, or neutral, and some variants can contribute to cancer. Some variants, such as BRCA, can be both somatic and germline.
Role of Biomarkers in Clinical Practice
Biomarkers influence oncology clinical practice in many essential ways. To communicate the role of biomarkers in personalizing care, oncology nurses must understand the different types of biomarkers.
- Diagnostic: Detect or confirm the presence of a disease or condition or identify those with a specific subtype (eg, PSA, HER2)
- Prognostic: Predictive of the likelihood of a clinical event, recurrence, or progression in a patient with a particular disease or condition
- Predictive: Identify patients more likely to experience a favorable/unfavorable response to treatment (eg, BRCA to determine response to PARP inhibitors in breast cancer)
- Monitoring: Repeated assessments of the status of a disease or condition following treatment (eg, PSA in prostate cancer)
In addition, biomarkers may help with symptom management. For example, with graft-versus-host disease (GVHD), biomarkers may help to identify patients at risk, confirm diagnosis, predict severity, and monitor response to treatment. Some stem cell transplant (SCT) centers test patients before and 1 week after SCT to help predict who might need more intensive treatment to minimize steroids when managing GVHD. Additional types of biomarkers include those measuring pharmacodynamic response, safety, and susceptibility/risk.
Understanding the role of biomarkers and how they affect oncology clinical practice is crucial to keeping up with the advancements in targeted therapies and how essential data can transform patient care. As more targeted therapies emerge, oncology nurses have an essential role in translating this knowledge into personalized care.
Understanding the role of biomarkers in treating cancer
National Cancer Institute: tumor markers
National Cancer Institute: dictionary of cancer terms
Oncology Nursing Society: biomarkers
Biomarkers of graft-vs-host disease: understanding and applications for the future