Abstract 26: Biomarker analysis of a male breast cancer patient with prolonged stable disease under mTOR/PI3K inhibitors BEZ235/RAD001

Abstract

Abstract The mTORC1 inhibitor RAD001 (everolimus) has been approved for multiple cancer indications, including ER+/HER2- metastatic breast cancer. The combination of RAD001 with a dual PI3K/mTOR inhibitor BEZ235 was shown to be even more efficacious than RAD001 alone in preclinical models and was evaluated in clinical trials. We identified a male breast cancer patient who experienced a prolonged stable disease with the RAD001/BEZ235 combination as 3rd line treatment for his metastatic disease and investigated molecular mechanisms to explain the extraordinary benefit and subsequent drug resistance. The 66-year old Caucasian male had stage IIIA invasive ductal carcinoma at initial surgery. He then received two sequential adjuvant therapies: a chemo-radiotherapy and letrozole. When the patient developed multiple metastases, he was treated with chemotherapy and then fulvestrant, before received a 200 mg twice daily BEZ235 and 2.5 mg weekly RAD001 combination regimen, when a left axillary nodal metastasis was developed on fulvestrant. The patient sustained a prolonged stable disease of 18 months while under the therapy before his tumor progressed again. Tumor biopsy samples (formalin fixed, paraffin embedded) were taken from the patient at diagnosis and after progression and analyzed by immunohistochemistry (IHC) and whole exome sequencing. Blood samples were collected for germline DNA pharmacokinetic (PK) analysis. PK profile of BEZ235 was collected with Cmax, AUC, and T1/2 of 766 ng/mL, 6308 ng.h/mL, and 5.53 h, respectively. The observed BEZ235 Cmin values ranged from 75.5 to 504 ng/mL over the study. The 2.5 mg weekly RAD001 dose is substantially lower than the standard 10 mg daily dose and the Cmin could not be reliably determined. IHC assays showed low ER/PR expression (ER 30% 1+; PR 20% 1+, 10% 3+) in the diagnosis sample, but an increase of their expression (60% 1+) in the post progression sample. HER2 expression was negative in both samples. Analysis the same tumor samples using more quantitative AQUA platform demonstrated a drastic 10-fold score increase of ER from 31 to 312 and a 5-fold increase of PR from 271 to 1305. All other examined signaling pathway biomarkers (e.g. pS6, pAKT, pMAPK, pMEK and pEGFR) were expressed in both tumor samples but showed minimal expression changes between the time points. Whole exome sequencing of the diagnosis and post-progression specimens provided average coverage at 142X and 179X, respectively . No functional somatic alterations resulting in hyperactive PI3K/mTOR pathway was detected in genes such as PIK3CA, PTEN, MTOR, TSC1/2 in either tumor samples. In both specimens, a somatic deletion of 16 bp was detected in SPEN, which encodes a potential negative regulator of the estrogen signaling pathway1 . In conclusion, no PI3K/mTOR pathway hyperactivity marker was identified in the diagnostic samples. However, the increased ER/PR expression in the post-progression sample suggests that the effect of PI3K/mTOR pathway blockade by RAD001/BEZ235 might have diminished when the tumor gained further dependence on the hormonal receptor signaling. This hypothesis was supported by the observation that the patient's tumor achieved another prolonged disease control of about 13 months by exemestane, after progression from BEZ235/RAD001 treatment. 1Légaré S, et al. SPEN is a novel candidate tumor suppressor gene that regulates response to tamoxifen in estrogen receptor positive breast cancers. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013. Citation Format: A. Rose Brannron, Davide Melisi, Jennifer Hummel, Carmine Carbone, Melissa Frizziero, Wing Cheung, Parul Patel, Jorge Gallo, Giampaolo Tortora, Michael Morrissey, David Chen. Biomarker analysis of a male breast cancer patient with prolonged stable disease under mTOR/PI3K inhibitors BEZ235/RAD001. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Integrating Clinical Genomics and Cancer Therapy; Jun 13-16, 2015; Salt Lake City, UT. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(1_Suppl):Abstract nr 26.