The current standard of care for detection of CRC in individuals over the age of 50 is colonoscopy. The compliance rate, however, is only about 60%, despite the fact that early detection typically results in better patient outcomes [13
]. And, colonoscopy miss-rates can exceed forty percent when patients do not comply with necessary bowel preparation procedures. This CRC serum assay is intended to provide individuals with important information regarding their own probability of having CRC, especially those who choose not to have a colonoscopy, which may in turn encourage individuals with a high probability of CRC by this assay to undergo a colonoscopy. When the probability of CRC is in the mid range for the assay (0.3-0.6), the patient’s decision will reflect his or her individual risk tolerance.
Because of the limitations of present screening methods, including colonoscopy and FOBT, there are several efforts underway to identify, confirm and validate serum biomarkers which could be used for routine CRC screening during annual physicals [4
]. Over the past several years, we have conducted such studies and have developed our protein-based serum assay, which simultaneously measures one peptide for each of seven proteins in serum. The tryptic peptides chosen for the assay are unique to the proteins being measured and are quantified using as little as 0.01 mL of serum. MRM LC/MS/MS cycle time is 4.5 minutes from the start of one sample to the start of the next sample, and sample preparation is relatively simple making the assay suitable for high-throughput techniques and broad implementation.
In this study we evaluated 431 samples, including 172 drawn from patients with CRC. Six of the seven peptides in the assay had an average concentration that was greater in CRC samples than in normal samples. This result mirrors the results from our discovery experiments as well as the data obtained for samples used during the development of the assay (unpublished results). One of the seven proteins, GSN, had a lower average concentration in CRC samples than in normal samples, as has been reported by others [5
]. None of the individual proteins provided high enough sensitivity to act as a single biomarker to determine the probability of CRC in a screening test. In our multivariate analysis we developed a model to achieve our goals of high sensitivity, 93.75% (95% CI, 69.77 - 99.84) and high specificity, 82.98% (95% CI, 73.84 – 89.95) with a prevalence adjusted NPV of 99.9775 % in the randomly chosen 110 sample test set.
The assay produces a probability of CRC as a number ranging from 0 to 1, the higher the number, the greater the probability of CRC. The 95% confidence interval around any probability calculated using the assay had a median halfwidth of 0.0968. A cut-off number (0.40) was chosen for the purpose of reporting the sensitivity, specificity and NPV of the model. Importantly, the probability of CRC determined by the assay does not correlate with age, gender or comorbidity, only stage of disease.
Because the samples analyzed in this study were from a single cohort, the results reported here will be further validated in a large multicenter prospective trial. Once successfully validated, this assay could be performed in parallel with other routine tests drawn during annual physical examinations. Results from this assay would provide physicians and patients with important information that could be used to assist in the decision as to the need for either an immediate colonoscopy or follow-up screening tests at established intervals.