Kristin Daly on the Difference Between Somatic and Germline Variants in Precision Oncology


Kristin M. Daly, MSN, ANP-BC, AOCNP, highlights the difference between somatic and germline variants.

Many individuals are surprised to learn that most cancers are driven by somatic variants and not germline variants, according to Kristin M. Daly, MSN, ANP-BC, AOCNP.

Daly, who is a nurse practitioner at Siteman Cancer Center at the Washington University in St Louis School of Medicine, recently delivered a Precision Medicine Primer and Case-Based Workshop as part of the nursing track at the 40th Annual Miami Breast Cancer Conference®. During her presentation, Daly explained the different between genetics and genomics, noting that genetics are the study of genes and their effects, and specifically, it is the study of how genes are inherited and can create conditions or illness. Genomics, on the other hand, is the study of all of an individual’s genes (their genomes) and how they interact with one another and with the environment within that person, and how this contributes to illness.1

Along with the difference between genetics and genomics, oncology nurses should understand the difference between somatic and germline variants.

As Daly outlined in her presentation, somatic variants are acquired. These are changes in the cells of the body or tumor that occur following conception. They are not inherited and will not be passed to children because they are not present in germ cells. Moreover, somatic variants can be positive, negative, or neutral.

In contrast, germline variants are inherited. These changes are present in the germ cells (sperm or egg) and are therefore present in every cell of an individual. These can be passed to children, and often thought of as risk or susceptibility biomarkers. However, these are less common oncogenic drivers; they only represent about 5% to 10% of cancers.2

“The vast majority of biomarkers that we’re going to be testing for are going to be somatic,” Daly emphasized. “[Somatic] comes from the word soma [meaning] body. So somatic [variants] are changes that have occurred in the body after conception. They are not inheritable.”

“People are often surprised to know that only about 5% to 10% of cancers are caused by germline or inherited variants,” she noted. “That even sometimes surprises some oncology nurses. I was surprised when I first found that out. Still, it’s important to know. In breast cancer, [individuals] can have both germline and somatic [variants] and it’s important to know which.”

She noted that in with breast cancer, there are women with germline BRCA mutations cancer, but that it is not always the case. As an oncology nurse, it is important to understand a patient’s individual cancer, and help them to understand the potential risk they could pass to children and descendants.

“We do have patients who have BRCA-positive cancer, but it’s not germline,” Daly explained. “That means it can’t be passed on to their children and their descendants. That’s important to know. You can understand how a patient might find that very confusing or be worried if we’re [to say] ‘You have this [variant], and we have this therapy.’ Patients, by and large, aren’t going to know the difference between germline and somatic.”


  1. Genetics vs. genomics fact sheet. National Human Genome Research Institute. Updated September 17, 2018. Accessed March 6, 2023.
  2. Mahon SM. Germline and somatic variants: what is the difference? ONS Voice. January 14, 2020. Accessed March 6, 2023.
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