DNA Yield From Tissue Samples in Surgical Pathology and Minimum Tissue Requirements for Molecular Testing

Abstract

Context Complex molecular assays are increasingly used to direct therapy and provide diagnostic and prognostic information but can require relatively large amounts of DNA. Objectives To provide data to pathologists to help them assess tissue adequacy and provide prospective guidance on the amount of tissue that should be procured. Design We used slide-based measurements to establish a relationship between processed tissue volume and DNA yield by A260 from 366 formalin-fixed, paraffin-embedded tissue samples submitted for the 3 most common molecular assays performed in our laboratory (EGFR, KRAS, and BRAF). We determined the average DNA yield per unit of tissue volume, and we used the distribution of DNA yields to calculate the minimum volume of tissue that should yield sufficient DNA 99% of the time. Results All samples with a volume greater than 8 mm3 yielded at least 1 μg of DNA, and more than 80% of samples producing less than 1 μg were extracted from less than 4 mm3 of tissue. Nine square millimeters of tissue should produce more than 1 μg of DNA 99% of the time. Conclusions We conclude that 2 tissue cores, each 1 cm long and obtained with an 18-gauge needle, will almost always provide enough DNA for complex multigene assays, and our methodology may be readily extrapolated to individual institutional practice.