Cytogenetic analyses of diagnostic (n=5259) and relapse (n=909) samples from patients with AML and ALL enrolled onto a prospective cytogenetic companion study, CALGB 8461 (5 (link)), were performed in multiple, currently 33, CALGB-approved institutional cytogenetic laboratories. Written IRB-approved informed consent was obtained from all patients. For each specimen, two karyotypes and metaphase spreads from each clone were submitted with the data on processing methods to the CALGB Cytogenetic Data Management Center. If applicable, images of interphase and/or metaphase cells subjected to fluorescence in situ hybridization (FISH) were also submitted. All cases underwent biannual central karyotype review performed by the CALGB Karyotype Review Committee consisting often expert cancer cytogeneticists. At central karyotype review sessions, every karyotype, metaphase spread, FISH image, and processing and interpretive data were reviewed by two cytogeneticists. In some cases, usually those with more complex chromosome abnormalities and/or with suboptimal banding quality, other reviewers also rendered their opinion. Once consensus was reached, each submission was judged as either acceptable with adequate banding quality, acceptable with borderline banding quality, or inadequate and consequently rejected. Reasons for rejection included poor banding quality that makes unequivocal karyotype interpretation impossible, and, only in cases with a normal karyotype, analysis of <20 metaphase cells from a marrow sample cultured for 24–48 hours or analysis of blood only (5 (link)). Since the aim of this study was to assess the role of central karyotype review, our analyses did not include 202 AML and 125 ALL cases for whom cytogenetic analysis yielded no metaphase cells.
In addition to data on rejection rates collected routinely at each central karyotype review, for the purpose of this study, we prospectively collected detailed information on the reasons for revisions made by central karyotype review in the submitted karyotypes that were accepted or borderline accepted during eight recent central karyotype review sessions. The reasons for revision were divided into the following categories: 1) major errors in karyotype interpretation, such as failure of the submitting laboratory to recognize a clonal abnormality, identification of an abnormality found on central karyotype review not to be present, and incorrect interpretation of an abnormality; 2) the need for refinement of breakpoint assignment in structural abnormalities properly recognized by the submitting laboratory, 3) misidentified or upside-down chromosomes, and 4) incorrect use of the ISCN (1995) nomenclature (47 ). In this study, we excluded samples analyzed cytogenetically during complete remission, because these samples differ from pretreatment and relapse samples in that they rarely contain leukemic cells and are usually karyotypically normal (48 (link)). The rejection rates between the first and the recent four-year periods (Table I) have been compared using the Fisher’s Exact test. All analyses were performed by the CALGB Statistical Center.