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DNA testing may reveal unknown genetic ancestry in triple-negative breast cancer
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Mitochondrial DNA testing may identify genetic ancestry that is discordant from self-identified ethnicity in patients with triple-negative breast cancer, according to study results published in Cancer.
The documentation of mitochondrial DNA (mtDNA) patterns may aid in the identification of genetic predispositions toward triple-negative breast cancer and aid in risk stratification, according to the researchers.
Triple-negative breast cancers do no express ER, PR or HER-2 receptors. These cancers are characterized by their aggressive histology and resistance to traditional breast cancer therapies.
Triple-negative breast cancers are predominantly seen in younger women and women of African American or Hispanic ancestry.
Research has shown that ethnicity may be related to response to neoadjuvant chemotherapy, as well as risk for toxicity from different chemotherapy regimens, in patients with triple-negative breast cancer.
“It is estimated that 10% to 30% of Americans may not be aware of their mixed ancestry,” Barbara B. Haley, MD, professor of internal medicine and Charles Cameron Sprague, MD, chair in clinical oncology at UT Southwestern Medical Center in Dallas, said in a press release. “This type of assessment has the potential to be informative for other cancers where we see ethnic differences in frequency without understanding the cause.”
Haley and colleagues conducted an analysis of mtDNA in 92 women (median age, 52 years) with triple-negative breast cancer at any stage of treatment or survival who self-identified as African American, white or Hispanic to define a hypervariable control region that may predispose individuals toward this cancer.
Of these women, 31 self-identified as African American, 31 self-identified as white, and 30 self-identified as Hispanic. The researchers confirmed each patient’s self-identification prior to buccal swab collection.
Self-identified Hispanic women had a younger median age (41 years) than African American women (53 years) or white women (57 years; P < .0001), were less likely to have a family history of breast cancer (P = .02), and presented with larger tumors (P = .01).
Eight women carried a BRCA mutation (African American, n = 2; white, n = 1; Hispanic, n = 5).
Self-identified racial analysis did not correlate with significant differences in surgery, lymph node metastases or OS.
The researchers used a commercially available assay to analyze patient mtDNA. They determined DNA sequence patterns through the use of a sequence similarity score and a database of 33,000 individuals of African lineage.
Seventy-seven percent (n = 21) of self-identified African American patients had Nigerian (n = 9), Cameroon (n = 8) or Sierra Leone (n = 5) ancestry. The researchers observed one discordance in this group, in which the mtDNA analysis of a self-identified African American woman indicated a haplogroup generally indicative of Native American or Hispanic ancestry.
The majority of self-identified white women (n = 20) exhibited associated with haplogroups indicative of white race/ethnicity. The researchers observed three discordances, suggesting Native American (n = 2) or Senegalese (n = 1) ancestry.
Hispanic women had a discordance rate of 26% (n = 8), the highest observed in the study.
Three women who self-identified as Hispanic had mtDNA indicative of Nigerian ancestry and one woman had mtDNA indicative of Sierra Leone ancestry. Additionally, one woman’s mtDNA was indicative of a haplogroup associated with Ashkenazi Jewish ancestry.
“Both African American and some Ashkenazi Jewish populations have a higher risk for triple-negative breast cancer,” Roshni Rao, MD, director of the George N. Peters, MD, Center for Breast Surgery at UT Southwestern Medical Center, said in a press release.
The overall study population had a 13% rate of discordance between their self-identified race/ethnicity and their genetic lineage.
“We found 12 differences among 92 patients — a significant amount,” Rao said. “If you know your ancestry, then you could be included in the group that gets screened at a younger age.” – by Cameron Kelsall
Disclosure: The researchers report no relevant financial disclosures.
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