Allelotype analysis of flow-sorted breast cancer cells demonstrates genetically related diploid and aneuploid subpopulations in primary tumors and lymph node metastases

Flow cytometric DNA content measurements have demonstrated extensive DNA pl oidy heterogeneity in primary breast carcinomas. However, little is known a t the molecular level about the clonal relationship between these tumor cel l subpopulations, or about the molecular genetic changes associated with an euploidization. We have used flow cytometric cell sorting to dissect some o f this complexity by isolating clonal subpopulations in breast carcinomas f or comparative molecular genetic analysis. Clonal subpopulations were isola ted from 12 primary breast carcinomas and 5 lymph node metastases from 4 ca ses based on DNA content and cytokeratin 8/18 labeling. DNA from these clon es was screened for allelic imbalances with 92 polymorphic microsatellite m arkers mapped to 39 different chromosome arms. Diploid and aneuploid popula tions were concurrently present in 11 out of 12 primary tumors. The DNA plo idy status of primary tumors was identical to that of the related lymph nod e metastases. Allelic imbalance was present in 10 out of 11 diploid clones (mean, 3.4 +/- 4.2). All allelic imbalances observed in the diploid clones recurred in the cognate aneuploid clones, but were, in the latter, accompan ied by additional allelic imbalances at other loci and/or chromosome arms ( mean, 10.9 +/- 5.8). In only two of the four metastatic cases did the allel otypes of metastatic clones show small differences relative to their cognat e primary tumors. The primary diploid tumor clone recurred in all lymph nod e metastases. This study indicates that the majority of allelic imbalances in breast carcinomas are established during generation of DNA ploidy divers ity. Recurrence of the allelic imbalances in diploid clones in the aneuploi d clones suggests linear tumor progression, whereas the simultaneous presen ce of early diploid and advanced aneuploid clones in both primary and metas tatic tumor sites suggests that acquisition of metastatic propensity can be an early event in the genetic progression of breast cancer. Genes Chromoso mes Cancer 28:173-183, 2000. (C) 2000 Wiley-Liss, Inc.