Hidden inherited cancer risks surface in routine tumor sequencing, oncologists warn

The practical framework outlined by Zhang and Madlensky arrives at a moment when the infrastructure of precision oncology is being tested by sheer volume. Tumor sequencing has shifted from an investigational tool available only at large academic centers to a routine diagnostic step across community oncology practices, and this democratization has outpaced the availability of genetics professionals who can interpret germline findings. The result is that many of the interpretive burdens described in the review—distinguishing somatic from germline events, recognizing suspicious variant allele frequencies, deciding when confirmatory testing is warranted—now fall on oncologists, oncology nurses, and advanced practice providers who may have received limited formal training in cancer genetics during their professional education. Educational initiatives from professional societies have begun to address this gap, but the pace of assay adoption continues to outrun the pace of workforce development, making practical guidance of the kind offered in this editorial particularly timely.

The biological logic underlying the two-hit model deserves further elaboration because it explains why germline findings in tumor reports so often correspond to specific tumor phenotypes. When a patient inherits a pathogenic variant in one copy of a tumor suppressor gene, the remaining functional copy in each cell acts as a safeguard against malignant transformation. Cancer arises in a given tissue only when that second copy is somatically damaged, which is why carriers of BRCA1 or BRCA2 pathogenic variants disproportionately develop tumors showing homologous recombination deficiency, and why carriers of Lynch syndrome genes develop mismatch repair deficient tumors that can be recognized by immunohistochemical loss of the corresponding proteins or by microsatellite instability on molecular testing. This relationship between germline genotype and tumor phenotype works in both directions: a pathologist or molecular oncologist who observes a characteristic tumor signature can reasonably suspect an underlying germline predisposition, and this suspicion should trigger consideration of confirmatory germline testing even when the patient did not meet traditional criteria based on family history alone.

The phenomenon of clonal hematopoiesis adds an important layer of complexity to the interpretation of high variant allele frequency findings, particularly in liquid biopsy results. Clonal hematopoiesis of indeterminate potential becomes increasingly common with age, and studies have suggested that a substantial fraction of individuals over seventy harbor detectable hematopoietic clones carrying mutations in genes such as DNMT3A, TET2, ASXL1, and TP53. When liquid biopsies are performed, these hematopoietic variants can be mistaken for tumor-derived mutations or for germline variants, since all three categories can present with elevated variant allele frequencies. Distinguishing among them often requires sequencing a matched buffy coat or saliva sample, and in cases where a hematologic malignancy is suspected, cultured fibroblasts provide a mesenchymal source of DNA that is unaffected by hematopoietic clonality. The review’s emphasis on this diagnostic nuance reflects a growing recognition that liquid biopsy results require careful contextual interpretation rather than reflexive action.

The observation that some laboratories simply filter out germline variants from paired tumor-normal reports without flagging them raises questions about transparency and consistency across the commercial testing landscape. Clinicians ordering paired sequencing may reasonably assume that a report lacking germline findings indicates the absence of germline variants, when in fact the laboratory may have applied internal filters that removed such variants from consideration entirely. This variability in reporting practices underscores the review’s recommendation that clinicians understand the workflow of the specific assay they have ordered. It also suggests a role for institutional molecular tumor boards, where clinicians, genetic counselors, pathologists, and laboratory directors can collectively review complex cases and clarify what a given report does and does not convey. Such multidisciplinary review has become an increasingly common mechanism for managing the interpretive challenges that arise as genomic testing proliferates.

The distinction between pathogenic variants and variants of uncertain significance carries practical consequences that extend beyond the individual patient. When a true pathogenic variant is identified in a patient with cancer, cascade testing of relatives becomes possible, allowing at-risk family members to learn whether they have inherited the same variant and to pursue appropriate surveillance or risk-reducing strategies. By contrast, a variant of uncertain significance cannot be used for cascade testing, since its clinical meaning remains unresolved. This asymmetry means that the distinction between these two categories has implications for entire families, not just for the individual patient. Genetic counselors play a critical role in communicating these distinctions to patients and their relatives, helping families understand why a VUS result does not change surveillance recommendations for family members even though it may feel significant to the patient who received it.

The reclassification dynamics of variants of uncertain significance represent an evolving area with real clinical consequences. As databases such as ClinVar accumulate evidence from functional studies, segregation analyses, population frequency data, and computational predictions, variants initially classified as uncertain may be reclassified as benign, likely benign, likely pathogenic, or pathogenic. The review notes that the majority of reclassified VUS ultimately prove to be benign or likely benign, which is reassuring but also means that patients who received a VUS result years ago may benefit from periodic re-evaluation of their original report. Some laboratories offer automatic reclassification updates to ordering clinicians, while others require proactive requests. Patients and clinicians who are unaware of this dynamic may continue to make clinical decisions based on outdated interpretations, or conversely may miss the opportunity to act on a variant that has been upgraded to likely pathogenic. Establishing a mechanism for tracking reclassification, whether through laboratory subscriptions, genetic counselor follow-up, or periodic chart review, represents a practical step that oncology practices can take to ensure that germline findings remain clinically current.

The review’s discussion of expanded versus focused panels touches on a tension that is likely to persist as genetic testing becomes more widespread. Expanded panels offer efficiency and can identify hereditary cancer syndromes that might not have been suspected based on personal or family history alone, particularly in adopted individuals or those with limited family information. However, the increased yield of uncertain and incidental findings creates a counseling burden that can overwhelm clinical encounters already constrained by time. Focused panels aligned with disease-specific guidelines reduce this burden but may miss predisposition syndromes outside the expected spectrum. The optimal balance between these approaches likely varies by clinical context, tumor type, and patient preference, and the review’s framework encourages clinicians to make these decisions deliberately rather than by default.

Finally, the editorial’s emphasis on confirmatory germline testing even when paired tumor-normal sequencing has identified a germline finding reflects the principle that clinical decisions with lifelong implications for patients and their families should rest on the most rigorous available evidence. Germline testing laboratories operate under different quality standards, use different assay designs, and provide interpretation within a framework specifically designed for hereditary cancer risk assessment. A finding that appears germline on a tumor-normal platform may require confirmation using blood, saliva, or other appropriate tissue, and in some cases may require additional testing such as RNA studies or deletion-duplication analysis that falls outside the scope of standard tumor sequencing panels. The practical considerations outlined in this editorial thus serve as a reminder that precision oncology, for all its technological sophistication, still depends on careful clinical judgment, clear communication among specialists, and a willingness to seek additional testing when the stakes for patients and their families are high.

Subject of Research: Precision oncology

Article Title: Tumor, germline, and paired testing in oncology: practical considerations

Article References: Zhang, X., & Madlensky, L. (2026). Tumor, germline, and paired testing in oncology: practical considerations. Supportive Care in Cancer, 34(10), Article 947. https://doi.org/10.1007/s00520-026-11177-w

Image Credits: AI Generated

DOI: 10.1007/s00520-026-11177-w

Keywords: germline testing, tumor sequencing, precision oncology, hereditary cancer, variants of uncertain significance, paired tumor-normal sequencing, clonal hematopoiesis, genetic counseling, cancer genetics, NGS, Lynch syndrome, BRCA