Abstract 2861: High-level amplification of chromosome 9p24 targeting PD-L1 and JAK2 correlates with worse DFS and OS in triple negative breast cancer
Authors: Anderson Karen S. , Klassen Christine L. , Dueck Amylou C. , McCullough Ann E. , Northfelt Donald W. , Andreozzi Mariacarla , Pockaj Barbara A. , Barrett Michael T. 
Published: August 2015

Introduction: Overexpression and amplification of PD-L1 has been reported in a subset of cancers, including lymphoma, and gastric cancer. We have recently described amplification of chromosome 9p24 targeting PD-L1 in a subset of triple negative breast cancers (TNBC), as well as 1-3% of colorectal carcinomas and glioblastomas. The clinical impact of these amplifications is not known.

Methods: Tumor samples from 41 subjects with TNBC were evaluated for copy number aberrations. We performed DNA-based flow cytometry to sort nuclei from diploid, tetraploid, and aneuploid populations of tumor cells. The genomes of each sorted tumor cell population were then interrogated with oligonucleotide CGH arrays. Copy number intervals were identified and their genomic boundaries mapped using a step gram algorithm. Clinical data was available on 36 of 45 (80%) patients.

Results: A recurring top ranked high level (log2ratio &gt;1) amplicon that spanned 9p24.1 was detected in 12/41 (29.3%) of TNBCs. In contrast this amplicon was absent in ER+ (n = 8) and Her2+ (N = 15) breast tumors. The shortest region of overlap (SRO) spanned 777 kb and always included the PD-1 ligands PD-L1, PD-L2, and Janus kinase 2 (JAK2) loci, termed the “PDJ” amplicon. Additional genes in this amplicon include RCL1, MIR101-2, INSL6, INSL4, RLN2, RLN1, and C9orf46. The height of the PDJ amplicon included mean log2ratios of &gt;4, consistent with genomic drivers such as Her2 and Myc. Patients with PD-L1 amplification (n = 8) were noted to have larger tumors (mean 3.9 vs. 1.9 cm, p = 0.04) and a higher incidence of lymph node metastases (75% vs. 26%, p = 0.01). Lymphocytic infiltration was only noted in 4 patients, all without PDJ amplification. Almost all patients received chemotherapy after definitive surgical therapy. The recurrence rate at 5 years was 62.5% in the PDJ amplified patients, and 25% in the unamplified patients (p = 0.02). Overall survival at 5 years was 37.5% in the PDJ amplified patients, compared with 78.2% in the unamplified patients (p = 0.02).

Conclusion: We identified a focal amplification of chromosome 9p24.1 involving PD-L1, PD-L2, and JAK2 in a significant proportion of TNBCs. The high level of amplification and inverse correlation with survival suggests that the PDJ amplicon is a genetic driver event in these cancers, and warrants confirmation in larger studies.

Citation Format: Karen S. Anderson, Christine L. Klassen, Amylou C. Dueck, Ann E. McCullough, Donald W. Northfelt, Mariacarla Andreozzi, Barbara A. Pockaj, Michael T. Barrett. High-level amplification of chromosome 9p24 targeting PD-L1 and JAK2 correlates with worse DFS and OS in triple negative breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2861. doi:10.1158/1538-7445.AM2015-2861