Slovak, Marilyn L.

11051 Background: A serious complication associated with breast cancer treatment is the increased risk for development of therapy-related acute myeloid leukemia (t-AML). To evaluate and possibly identify patients (pts) at high risk for development of t-AML, the Southwest Oncology Group asked whether dose-intensive adjuvant regimens for high risk breast cancer pts induced genetic damage to hematopoietic stem cells (HSC), defined by the emergence of clonal hematopoiesis, an early marker of HSC damage. Methods: 274 pts consented to the clonal hematopoiesis study objective of S0012, a randomized clinical trial of standard doxorubicin and cyclophosphamide followed by weekly paclitaxel (arm 1, 129 pts) vs. weekly doxorubicin and daily oral cyclophosphamide plus G-CSF followed by weekly paclitaxel (arm 2, 145 pts) as neoadjuvant therapy for inflammatory and locally advanced breast cancer. Two different clonality assays were used: the HUMARA (HUMan Androgen Receptor) Assay to estimate the incidence of early genetic damage by clonal proliferation and microsatellite instability (MSI) testing at 5 loci (Bat 26, Bat 40, APC, Mfd, D2S123), common ‘hotspots‘ in t-AML, to screen for loss of heterozygosity or defective DNA mismatch repair mechanisms. Blood samples were evaluated prior to treatment and at 6 and 12 mos post-surgery for emergence of clonal hematopoiesis. Results: Of the 274 pts enrolled, follow-up clonal hematopoiesis samples were available for 195 pts; 96 pts on arm 1 and 99 pts on arm 2. Both HUMARA and MSI results were negative for clonal hematopoiesis in 96% of samples analyzed. In 14 cases, the HUMARA assay suggested that a clonal population was present, but MSI analysis was negative. No cases were HUMARA+/MSI+. With a median follow-up of 19.6 mos, only one pt has developed t-AML 3 yr 5 mos post randomization. Her clonal hematopoiesis test samples at 6 and 12 mos following treatment were negative. Conclusions: Clonal hematopoiesis assays performed within the first year following neoadjuvant therapy and surgery on S0012 failed to identify an emerging clonal HSC population. Longer clinical follow-up will be necessary to define the positive predictive value of detecting clonal hematopoiesis in the 14 HUMARA+/MSI- cases as a harbinger of t-AML. No significant financial relationships to disclose.

Abstract Abstract 2922 The myelodysplastic syndromes (MDS) are a heterogeneous group of hematological malignancies characterized by ineffective hematopoiesis and a highly variable clinical course, for which novel treatments are beginning to emerge. Conventional cytogenetic studies (CCS) of bone marrow (BM) are routinely used in clinical practice to detect abnormal clones in proliferating (metaphase) cells, identifying clonal aberrations in ∼50% of de novo MDS cases. Cytogenetics is also one of the key International Prognostic Scoring System (IPSS) components used to estimate overall survival and leukemia-free survival in MDS. Chromosome abnormalities may be quantified at presentation and during treatment by the use of fluorescence in situ hybridization (FISH) with DNA probes for specific chromosome loci (e.g., chromosomes 5, 7, 8 and 20) in non-proliferating (interphase) nuclei. However, it is not clear whether or not peripheral blood CCS will yield the same diagnostic and prognostic data as bone marrow CCS at disease presentation or whether patients without apparent chromosome abnormalities by CCS have “hidden” abnormalities that can be identified by interphase FISH. To answer these questions, 15 members of the International Working Group on MDS Cytogenetics agreed to perform CCS and FISH in parallel on both peripheral blood and bone marrow samples collected from MDS patients. To be certain that all participating sites scored and interpreted their individual FISH data in a similar fashion, a quality assurance (QA) study was completed with each site studying two identical test (proficiency) samples. Concordance among sites was very good to excellent allowing for the establishment of a standardized protocol with clear scoring criteria before patient samples were processed. In the second phase of the study, a total of 77 MDS patients were accrued to the study with 61% showing an abnormal karyotype. A FISH panel consisting of eight probe sets [-5/5q-, -7/7q-/der(1;7), +8/8q-, -11/+11/11q-/add(11q), 12p-/+21/t(12;21), -13/13q-, 17p- and 20q-/i(20q)/i(20p), Abbott Molecular, Inc.] was performed on both specimen types. While CCS was frequently unsuccessful (57.5%) in the PB specimens, FISH was informative (concordant with BM/PB CCS) in 92% of cases, with 49% of PB FISH demonstrating an abnormal clone. FISH was discordant in 4 of 77 BM and PB samples (5%), while CCS and FISH on BM and PB were discordant in 6 of 77 BM specimens (8%) and 6 of 73 PB specimens (8%). The data suggest that evaluation of interphase nuclei from PB on follow-up (non-diagnostic) FISH studies on MDS patients will be equally informative (and less costly and stressful) as a BM sample. Disclosures: Slovak: PerkinElmer: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership, Research Funding. Ohyashiki:Nippon Shinyaku Co., Ltd.: Research Funding.