2.8. Statistical analysis
Statistical evaluation was performed with Graph pad prism
for categorical variables. Fisher exact test was performed in
the instance of 2 and 3 variables.
(G12D) and of DNA from MCF-7 cells, that have wt KRAS, and
then spiked the DNA from the PANC1 cells into the DNA
from the MCF-7 cells. The results show that this assay is
able to discriminate at least 5 copies of mutant allele for
100,000 wt copies (i.e. an abundance ratio of 0.05%)
(Figure 1C and D). Additionally, we found that the performance
of ddPCR is at least 10-fold more sensitive than TaqMelt
(using Cobas z480) and HRM (using LC480 analyzer)
with a sensitivity limit for both techniques close to 0.5e1%
(Supp. Data 1). Next, we compared the capacity of ddPCR,
Sanger sequencing, TaqMelt and HRM to detect KRAS mutant
cells in whole blood (Figure 2). For this purpose, we spiked 100,
75, 50, 10 or 5 cells into healthy donor blood and then used the
size-based ScreenCell technology to enrich the fraction of
mutant cells from the leucocyte background. Next, DNA was
extracted and amplified from the enriched cell fraction and
then processed by the different molecular detection methods.
For ddPCR, we defined a threshold after processing of three independent
samples from healthy blood donor as “mean of the
abundance ratio þ 3 SD” thereby allowing us to fix the