Abstract P5-09-03: Expression of the C9Orf72 long-isoform in cancer tissues prognosticates disease-free and breast cancer-specific survival
Authors: Chaher Nabila , Madan Esha , Qualls Clifford , Royce Melanie , Kuppusamy Periannan , Gogna Rajan , Arias-Pulido Hugo 
Published: May 2015

Background: An expansion of the GGGGCC hexanucleotide repeat in C9Orf72 gene promoter results in reduced mRNA expression of its long-isoform, and has been associated with amyotrophic lateral sclerosis, and frontotemporal dementia. Over-expression of C9Orf72 in cultured neuronal cells resulted in increased cell death, but its role in oncogenesis and, specifically, in brain metastasis is unknown.

Materials and Methods: C9Orf72 mRNA levels were measured by qPCR in 200 normal breast, 217 (cohort 1) and 100 (cohort 2) breast tumor samples, and correlated with clinico-pathological variables, breast cancer-specific (BCSS) and disease-free survival (DFS). MCF-7 tumor xenografts models were used to observe the effect of C9Orf72 on tumor metastasis.

Results: C9Orf72 mRNA levels were statistically higher in tumor than in normal breast tissues (P&lt;0.0001). In cohort 1, comprised of 117 inflammatory and 100 locally-advanced breast cancers, C9Orf72 levels were (1) low in IBC than in LABC (P=0.79); (2) statistically significant lower in cohort 1 than in cohort 2 (P&lt;0.001); and (3) associated with local and distant recurrences (P&lt;0.001) in both cohorts. Kaplan-Meier analysis showed that low C9Orf72 levels were associated with both worse DFS and BCSS in the two cohorts (P&lt;0.0001 for both). Cox proportional hazards model determined that ER status (Hazard Ratio [HR] = 0.65; 95%CI=0.44-0.98; p=0.04), lymph node ratios (HR=1.84; 95%CI=1.19-2.84;p=0.006), and low C9Orf72 levels (HR=37.4; 95%CI=17.08-81.72; p&lt;0.0001) were prognosticators of DFS; and low C9Orf72 levels (HR=7.02; 95%CI=4.1-12.1; p&lt;0.0001) were associated with worse BCSS in the training-cohort. In the validation cohort, low C9Orf72 levels were associated with worse DFS (HR=291.1; 95%CI=16.6-5121.1; p&lt;0.0001). Tumor grade (HR=2.5; 95%CI=1.59-3.8; p&lt;0.0001), and low C9Orf72 levels (HR=6.9; 95%CI=3.6-13.2; p&lt;0.0001) were independent prognostic factors of worse BCSS. Overexpression of C9Orf72 in a MCF-7 orthotopic mouse xenograft also resulted in significant tumor regression and reduced metastatic events to inguinal, axillary lymph nodes, pancreas, liver and kidney.

Discussion: C9Orf72 low levels were highly specific and sensitive prognostic factors of worse DFS and BCSS in two demographically distinct cohorts of breast cancer patients, and increased C9Orf72 expression resulted in reduced metastatic events in a mouse xenograft model. The molecular mechanisms of C9Orf72-induced cell death are unknown and warrant deep investigation because of its possible association with brain metastasis. C9Orf72 has the potential to emerge as a very attractive prognostic biomarker and potential therapeutic candidate in breast cancers.

Senior authors: RG, HAP. This work was partially funded by GlaxoSmithKline ERI grant.

Citation Format: Nabila Chaher, Esha Madan, Clifford Qualls, Melanie Royce, Periannan Kuppusamy, Rajan Gogna, Hugo Arias-Pulido. Expression of the C9Orf72 long-isoform in cancer tissues prognosticates disease-free and breast cancer-specific survival [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-09-03.