Have You Seen This?: Somatic vs Germline Discrepancies

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Holly Magliochetti

Genetics Institute of America

Genetics Institute of America (GIA) is a national laboratory dedicated to heightening the awareness of early intervention and genetic screening to promote the longevity and quality of life outcomes.  


Have You Seen This? 

Is Somatic Tumor Testing Sufficient for Proper Patient Care?

DELRAY BEACH, FL  – Somatic tumor genetic testing is becoming more common in oncology to understand a patient’s prognosis, eligibility for clinical trials, and targeted treatment opportunities. This type of testing isolates tumor tissue and identifies variants associated with cancerous growth. However, clinicians are not always referring patients for additional germline testing after receiving somatic testing results. Somatic testing is different than germline genetic testing, which seeks to identify genes associated with hereditary cancer syndromes. “Utilizing both [somatic tumor testing] and germline genetic testing when appropriate yields the highest likelihood of finding clinically actionable results that could impact patient care and familial cancer screenings.”1

Only using somatic tumor testing or germline testing could result in discrepancies within results and fail to yield the necessary information for improved patient outcomes. “Differing variant classification methods, intentional exclusion of germline variants on [somatic] reports, low variant allele fraction, and allelic drop out all may lead to discrepancies between PVs found by [somatic] and designated germline genetic testing.”1

A study funded by the National Cancer Institute and the University of Utah found that “germline testing identified actionable genetic aberrations in PV’s that were not detected by somatic testing. This led to treatment changes for the affected patients and impacted the care of patient’s relatives.” 1 Multiple individuals within the study’s cohort underwent somatic testing before germline testing and “these results would not have been known and these patients and their family members would have missed cancer screening opportunities to reduce their risk of diagnosis of cancer at late stage” and targeted treatment opportunities. 1

“Somatic testing was not found to be an equivalent proxy for germline genetic testing in this study” and, based on the study results, “clinicians should refer patients [for germline testing] who meet the criteria for genetic evaluation regardless of somatic testing outcomes.”1

  1. Pauley K, Koptiuch C, Greenberg S, et al. Discrepancies between tumor genomic profiling and germline genetic testing. ESMO Open. 2022;7(4):100526. doi:10.1016/j.esmoop.2022.100526
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