Hypoxia marker labeling in tumor biopsies: quantification of labeling variation and criteria for biopsy sectioning

The error associated with using biopsy-based methods for assessing parameters reflective of the tumor microenvironment depends on the variability in distribution of the parameter throughout the tumor and the biopsy sample. Some attention has been given to intratumoral distribution of parameters, but little attention has been given to their intrabiopsy distribution. We evaluated the intrabiopsy distribution of CCI-103F, a 2-nitroimidazole hypoxia marker.

The hypoxia marker CCI-103F was studied in dogs bearing spontaneous solid tumors. Two biopsies were taken from each of seven tumors, for a total of 14 biopsies. Biopsies were serially sectioned and four to six contiguous slides from each 100-150 microm of the biopsy were used to formulate the best estimate of CCI-103F labeled area throughout the biopsy sample. One, two or four slides were then randomly selected from each biopsy and the labeled area, based on this limited sample, was compared to the estimate obtained from counting all available slides. Random sampling of slides was repeated 1000 times for each biopsy sample.

CCI-103F labeling variance throughout the biopsy decreased as the estimated overall labeled area in the biopsy decreased. The error associated with estimating the overall labeled area in a biopsy from a randomly selected subset of slides decreased as the number of slides increased, and as the overall labeled area in the biopsy decreased. No minimally labeled biopsy was classified as unlabeled based on limited sampling.

With regard to CCI-103F labeling, quantification of the labeled area in four randomly selected slides from a biopsy can provide, in most biopsies, an estimate of the labeled area in the biopsy within an absolute range of +/-0.05.