Detection of false DNA aneuploidy and false DNA multiploidy in flow cytometric DNA analysis

Although false DNA aneuploid peaks have previously been described in normal tissue, criteria for distinguishing them from 'true' near-diploid peaks have not been established. Normal thyroid (n = 4) and kidney (n = 1) tissue were allowed to autolyze over a fixed period of time and DNA content was analyzed by flow cytometry (FCM). Autolysis was associated with the development of distinct separate G0/G1 peaks which had low DNA indices (1.09-1.18) and showed decreased forward light scatter (FSC) when compared to fresh tissue. Using DNA content and FSC measurements similar false DNA aneuploid peaks were identified in 29/94 surgical specimens. These cases included both benign and malignant lesions from thyroid (n = 63) with the remaining 31 neoplastic cases being from breast (16), lymphoma (8), sarcoma (4), lung (2) and uterine (1) tissue. In addition, false DNA multiploidy was identified. None of these cases showed histological evidence of necrosis. In a parallel comparison study using image cytometry (ICM) on the thyroid nodules, the presence of false DNA aneuploidy was supported. Investigators should routinely employ quality control criteria to identify possible cases of false DNA aneuploidy when measuring DNA content using FCM.