Profiling of breast cancer plasma proteins by ICAT. (A) Spectral count (total number of peptides) as a function of peptide count (number of unique peptides). Lower part is an enlarged view of spectral count ≤ 10 vs. peptide count. (B) Peptide count as a function of normalized rank of quantified proteins. Solid line: current data set, dashed line: tissue extract data set retrieved from  and reprocessed. (C) A quantile-quantile plot of the peptide quantification distribution. The percentiles of the logarithms of heavy-to-light peptide ratios are plotted against the percentiles from a normal distribution. (D) Profile of protein ratios. The ratios are log2-transformed. Bin size: 0.2.