Bodily Fluids Other Than Blood May Yield Clinically Relevant ctDNA in Breast Cancer

By: Liam Andrew Davenport, MA (Hons)

From: oncologynurseadvisor.com

Circulating tumor DNA (ctDNA) is detectable not only in peripheral blood samples but in many other bodily fluids, which may offer additional information when peripheral blood samples are inconclusive, suggests a comprehensive analysis of fluids and metastatic tissue from women with breast cancer.

The results also indicate that ctDNA levels in different bodily fluids may point to the presence of neighboring metastatic sites, and that alternative samples could contain oncogenic mutations not present in blood draws, study researchers report.

These findings were published in Nature Communications.

The UPTIDER study (NCT04531696) is a tissue donation program involving 20 women with metastatic breast cancer, of whom 4 women were de novo metastatic cases, while 16 relapsed after primary diagnosis. They were enrolled between December 2002 and September 2022, and all subsequently died.

The most common cancer type among the women was hormone receptor (HR)-positive/HER2-negative, in 16 cases, followed by triple-negative breast cancer in 3 cases. There was 1 case of HR-positive/HER2-positive breast cancer. The median time between primary diagnosis and death was 7.25 years.

The presence of ctDNA was assessed in 7 bodily fluids: ascites; blood, both peripheral and central; cerebrospinal fluid (CSF); pericardial fluid; left and right pleural fluid; saliva; and urine. Metastatic tumor samples were also taken. A median of 46 tumor and liquid samples were taken per patient, with a median of 6 tumor and 4 liquid samples taken during their lifetime.

Low-pass whole-genome sequencing was performed on a total 216 liquid and 745 metastatic tissue samples from the 20 patients, and whole-exome sequencing was carried out on 86 fluid samples from 11 patients to examine their mutational status.

Analysis of blood samples taken at different times indicated that ctDNA was detected in 50% of patients after they developed metastatic disease, in 69% after they were included in the program, and in 75% at autopsy, “highlighting the dynamic nature of the disease and ctDNA status,” the researchers wrote.

At autopsy, the detection rate of ctDNA was 92% in ascites, 80% in pleural fluid, 75% in peripheral blood, 67% in CSF, 63% in central blood, 36% in pericardial fluid, and 27% in urine. In the 40% of patients for whom peripheral blood was uninformative, ctDNA was detected in ascites in 75% of cases, as well as in pleural fluid (75%), CSF (50%), pericardial fluid (25%), and central blood (13%).

“Taken together, these results show that ctDNA can be detected in alternative body liquids than peripheral blood,” the researchers wrote.

It was also shown, for example, that ctDNA levels tended to be higher in pleural fluid and CSF when metastases were present in the pleura and central nervous system, but ctDNA fractions in ascites and urine were not linked to the presence of peritoneal and bladder invasion. This suggests that ctDNA related to metastatic sites can be specific to a bodily fluid, and so liquids other than peripheral blood “can provide complementary information,” the researchers noted.

Moreover, ctDNA relating to oncogenic mutations was found at differing rates depending on the fluid sampled: at 64% for peripheral blood, 56% for ascites, 55% for central blood, 50% for pleural fluid, 44% for pericardial fluid, 30% for CSF, and 25% for urine, although copy numbers were more stable.

These findings “indicate that non-blood fluids frequently capture alterations that are not observed in blood, some of which may have potential clinical relevance,” the researchers wrote.

“While promising, the prognostic clinical utility of liquid biopsy-based monitoring, potentially including multiple liquid biopsy sources, is still to be proven,” the researchers added. “The psychological burden imposed on patients by such monitoring should also be considered in future clinical applications and included in the risk-benefit analysis of these tests, preferably after thorough discussions with patient advocacy groups.”