cfDNA Flashcards
Current clinical uses of cfDNA
Noninvasive prenatal testing
Monitoring solid organ transplantation
Predictive biomarker for treatment selection in NSCLC
Variations in cfDNA
The quantity of circulating cfDNA:
* varies between individuals
* varies between physiologic states and pathologic conditions
* is elevated following traumatic injury and with infarction, pregnancy, and cancer
When is fetal cfDNA first detectable in maternal blood?
About 10 weeks eGA
What are some reasons it may take longer for cfDNA to be detectable in some pregnancies?
High maternal BMI
Some aneuploidies
Pregnancies resulting from assisted reproductive technologies
Confined placental mosaicism
May cause false positive results in cfDNA, making the cfDNA profile look like aneuploidy
cfDNA in assessment of transplanted solid organ rejection
The fraction of donor-derived cfDNA can be measured via SNP genotyping, HLA genotyping, copy number polymorphisms, and Y-chromosome measurements (in sex-mismatched patients).
The PPV of elevated cfDNA for rejection is low, as it is nonspecific and may be elevated in a variety of conditions affecting the graft. However, the sensitivity is good, and it may serve as a noninvasive monitoring tool.
Factors that predict the presence of detectable ctDNA in surgically resectable NSCLC
Squamous morphology
High tumor cell proliferation rate
Presence of LVI
cfDNA tends to come in increments of 150 bp (150, 300, 450bp . . .) because. . .
This is the number of bases it takes to wrap around a nucleosome
150 bp = 90%
300 bp = 9%
450 bp = 1%
Collecting ctDNA specimens
Use an EDTA or leukocyte stabilization tube (like CellSave).
Both work when plasma is isolated within 6h of collection, but leukocyte stabilization preparations work much farther out (>48 hours).
4 degrees C and room temperature storage are both fine. Freezing is fine too, although freeze-thaw cycles will gradually reduce yield.
The general principle is to collect, store at 4 degrees C until plasma is isolated, and isolated as soon as possible.
