Abstract PD7-08: Gene Expression Profiling of Breast Cancer Brain Metastasis shows enrichment for non-luminal subtypes with potential prognostic implications

Abstract Background: The incidence of breast cancer (BC) brain metastases (BM) is increasing as a result of both improved diagnostic techniques and longer survival due to better treatment approaches. However, the biological complexity of BCBMs is still poorly understood. We here evaluate the genomic profile of BCBMs and assess its prognostic implications. Methods: Clinical data and BM samples (FFPE) from BC patients undergoing neurosurgery (2003-2019) at three institutions were collected. Hormone receptor (HR) and HER2 status were evaluated on the BCBM. RNA extracted from BM samples was used to measure the expression of 758 BC–related genes and 18 housekeeping genes using the Breast Cancer 360 Panel on an nCounter platform (NanoString Technologies). Intrinsic molecular subtyping was determined using the previously reported PAM50 subtype predictor (Parker et al. JCO 2009). Median overall survival from neurosurgery (OS) was calculated using the Kaplan-Meier method. The correlations between expression of each gene/PAM50 signature, BC subtype and OS were studied using univariate and multivariate Cox-models. Results: Sixty-five BCBM samples were analyzed: 32% (N=21) were HR+/HER2-, 38% (N=25) HER2+ and 29% (N=19) HR-/HER2-. With a median follow-up of 33 months, no clinical variable was significantly associated with OS, despite a trend towards a shorter survival for patients with HR-/HER2- BMs, as compared to patients with HR+/HER2- and HER2+ subtypes (median OS 9.4 versus 22.1 and 20.0 months, respectively, log-rank p=NS). The intrinsic subtype distribution, as assessed by gene-expression profiling, was 37% Basal-like, 46% HER2-enriched (HER2-E), 15% Luminal B and 2% Normal-like. Non-luminal subtypes (basal-like and HER2-E) were extensively represented, both overall and in each BC subtype (52% in HR+/HER2- subgroup, 96% in HER2+ subgroup, see Table). The PAM50 basal-like signature was significantly associated with a worse OS (HR 2.7, 95% CI 1.0-7.2, p=0.045), even after correcting for BC subtype (HR 5.2, 95% CI 1.1-23.4, p=0.032). In fact, even within the subgroup of HR+/HER2- BCBMs, the PAM50 basal-like signature was strongly associated with a worse OS (HR 92.6, 95% CI 5.0-1860.1, p=0.003) and patients with basal-like HR+/HER2- BCBMs presented a median OS similar to patients with HR-/HER2- BCBMs (mOS 9.0 vs 9.4 months). We identified 36 genes whose high expression was significantly associated with a worse OS (p< 0.05) and one gene (LINC02381) whose high expression was significantly associated with better OS (p< 0.05); for 33 of these genes (BCL11A, BMP2, BNIP3, CAV1, CDH3, CDK6, CKB, CRYAB, CXCL12, EGFR, EYA4, FOXC1, FZD8, FZD9, GABRP, GAS1, GDF5, GPC4, IL6, KRT17, KRT5, KRT6B, KRT7, LAMB3, LINC02381, MYC, NOTCH1, PRKX, PSAT1, RUNX3, SNAI1, SPRY2, TTYH1), the association was confirmed even after correcting for BC subtype (p< 0.05). Conclusions: Non-luminal intrinsic subtypes are extensively represented in resected BCBMs, even if clinically classified as HR+/HER2-. Our data suggest that basal-like genomic features might be enriched in BCBMs and might be associated with worse survival. Distribution of PAM50 intrisic subtyping on the 65 brain metastases evaluated according to hormone receptor (HR) and HER2 status Citation Format: Gaia Griguolo, Maria Vittoria Dieci, Susan Fineberg, claudia Pinato, Michele Bottosso, Luc Bauchet, Federica Miglietta, Jack Jacob, Giovanni Zarrilli, Valérie Rigau, Maria Cristina Guarascio, Francesca Zanconato, Francesca Schiavi, Matteo Fassan, William Jacot, Stefano Piccolo, Amelie Darlix, Valentina Guarneri. Gene Expression Profiling of Breast Cancer Brain Metastasis shows enrichment for non-luminal subtypes with potential prognostic implications [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD7-08.