Volume of preclinical xenograft tumors is more accurately assessed by ultrasound imaging than manual caliper measurements.
OBJECTIVE
The volume of subcutaneous xenograft tumors is an important metric of disease progression and response to therapy in preclinical drug development. Noninvasive imaging technologies suitable for measuring xenograft volume are increasingly available, yet manual calipers, which are susceptible to inaccuracy and bias, are routinely used. The goal of this study was to quantify and compare the accuracy, precision, and inter-rater variability of xenograft tumor volume assessment by caliper measurements and ultrasound imaging.


METHODS
Subcutaneous xenograft tumors derived from human colorectal cancer cell lines (DLD1 and SW620) were generated in athymic nude mice. Experienced independent reviewers segmented 3-dimensional ultrasound data sets and collected manual caliper measurements resulting in tumor volumes. Imaging- and caliper-derived volumes were compared with the tumor mass, the reference standard, determined after resection. Bias, precision, and inter-rater differences were estimated for each mouse among reviewers. Bootstrapping was used to estimate mean and confidence intervals of variance components, intraclass correlation coefficients (ICCs), and confidence intervals for each source of variation.


RESULTS
The average deviation from the true volume and inter-rater differences were significantly lower for ultrasound volumes compared with caliper volumes (P = .0005 and .001, respectively). Reviewer ICCs for ultrasound and caliper measurements were similarly low (1%), yet caliper volume variance was 1.3-fold higher than for ultrasound.


CONCLUSIONS
Ultrasound imaging more accurately, precisely, and reproducibly reflects xenograft tumor volume than caliper measurements. These data suggest that preclinical studies using the xenograft burden as a surrogate end point measured by ultrasound imaging require up to 30% fewer animals to reach statistical significance compared with analogous studies using caliper measurements.
Ayers
Gregory D
GD
Department of Biostatistics, Vanderbilt University Medical Center, Nashville, TN 37232-2310, USA.
McKinley
Eliot T
ET
Zhao
Ping
P
Fritz
Jordan M
JM
Metry
Rebecca E
RE
Deal
Brenton C
BC
Adlerz
Katrina M
KM
Coffey
Robert J
RJ
Manning
H Charles
HC
D000704:Analysis of Variance; D000818:Animals; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D016001:Confidence Intervals; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D051379:Mice; D008819:Mice, Nude; D010808:Physical Examination / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D014183:Transplantation, Heterologous; D014463:Ultrasonography / Q000379:methods*