I'm going to study the expression of a particular micro-RNA in tumor samples in comparison to normal tissue. We obtain gastric tumor and normal samples from same patient. How many samples do we need to our results be valid for differential expression study and investigating the micro-RNA of interest as biomarker? is there any authentic guideline or article as reference? Thanks for your help.
I understand from a recent presentation that the initial developmental number are likely to be very much smaller than with comparisons between tissues from different patients, and an N=20 was discussed as reasonable minimum [given 40 from independent samples had appeared adequate in previous studies]. However, follow-up valuation of the initial results -- on an independent set of gastric cancer patients -- should be large enough to detect a preselected failure to detect rate [e.g., say
One more "biomarker study"...
What predictive value(s) should the biomarker have? Spot these values and you get an impression of how many samples wou will need to at least get these values when the discrimination is perfect. You can make a pilot study with 20-40 patients and see what discrimination you can expect and mprove your guess about the required sample size.
It depends on the power of study, the percent of confidence (almost 95%) and the previous results from same study (if not exist, just do a pilot with 20 samples and use the results to calculate the statistical sample size).
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