Hagemann, Ian S.

BACKGROUND Treatment of tubo-ovarian high-grade serous carcinoma (HGSC) includes cytoreductive surgery, platinum-based chemotherapy, and often poly(ADP-ribose) polymerase (PARP) inhibitors. While homologous recombination (HR) deficiency is a well-established predictor of therapy sensitivity, over 50% of HR-proficient HGSCs also exhibit sensitivity. Currently, there are no biomarkers to identify which HR-proficient HGSCs will be sensitive to standard-of-care therapy. Replication stress may serve as a key determinant of response. METHODS We evaluated phospho–RPA2-T21 (p-RPA2) foci via immunofluorescence as a biomarker of replication stress in formalin-fixed, paraffin-embedded HGSC samples collected at diagnosis from patients treated with platinum chemotherapy (discovery cohort, n = 31; validation cohort, n = 244) or PARP inhibitors ( n = 63). Recurrent HGSCs ( n = 38) were also analyzed. p-RPA2 score was calculated using automated imaging analysis. RESULTS Samples were defined as p-RPA2-high if more than 16% of cells had ≥2 p-RPA2 foci on automated analysis. In the discovery cohort, HR-proficient, p-RPA2-high HGSCs demonstrated significantly higher rates of a chemotherapy response score of 3 to platinum chemotherapy than HR-proficient, p-RPA2-low HGSCs. In the validation cohort, patients with HR-proficient, p-RPA2-high HGSCs had significantly longer survival after platinum treatment than those with HR-proficient, p-RPA2-low HGSCs. Additionally, the p-RPA2 assay effectively predicted survival outcomes in patients treated with PARP inhibitors and in recurrent HGSC samples. CONCLUSION Our study underscores the importance of considering replication stress markers, such as p-RPA2, alongside HR status in therapeutic planning. This approach has the potential to increase the number of patients receiving effective therapy while reducing unnecessary toxicity. FUNDING The Reproductive Scientist Development Program, GOG Foundation, Pilot Translational and Clinical Studies function of the Washington University Institute of Clinical and Translational Sciences, the Foundation for Barnes-Jewish Hospital, Washington University School of Medicine Dean’s Scholar Program, The Cancer Biology Pathway Training Grant (5T32CA113275-17), The Lucy, Anarcha, and Betsey (L.A.B.) Award from the Department of Obstetrics and Gynecology at Washington University School of Medicine, and Veterans Affairs Office of Research and Development (I01BX006020).

Abstract Background Patients (pts) with ER+ HER2+ breast cancer (BC) are less likely to achieve pathological complete response (pCR) after neoadjuvant chemotherapy with dual HER2 blockade than pts with ER- HER2+ BC. Endocrine therapy (ET) plus trastuzumab is effective in advanced ER+ HER2+ BC, but pCR rate is low in the neoadjuvant setting. Inhibition of CDK4/6 and HER2 results in synergistic reduction in cell proliferation in preclinical studies. We therefore combined ET with CDK4/6 inhibition and trastuzumab in ER+ HER2+ BC as a chemotherapy-sparing regimen. Methods We evaluated the efficacy of palbociclib, letrozole, trastuzumab (PLT) in the neoadjuvant setting for pts with stages II or III ER+ HER2+ BC. Primary endpoint was pCR after 16 weeks of therapy. We assumed null of 15% pCR and pCR ≥ 30% warrants further investigation. To achieve 80% power at 1-sided 0.05 significance, 48 pts were to be enrolled. Evaluable population included pts who completed Cycle (C) 1 unless discontinued due to treatment-emergent adverse events (TEAEs) prior to completing C1. All who received one dose on study were considered evaluable for toxicity. Biopsies were collected at baseline (BL), C1 day 15 (C1D15), and surgery for RNA sequencing and central Ki67 assessment, for PAM50 subtype distribution, complete cell cycle arrest (CCCA: Ki67 ≤2.7%) at C1D15 and surgery, and treatment induced signaling changes. Results Accrual stopped early due to futility. 26 pts accrued were evaluable for efficacy and toxicity. pCR (residual cancer burden- [RCB] 0) was 7.7% (95% CI 0.9 - 25.1%) and RCB 0/I was 38.5% (95% CI 20.2 - 59.4%). TEAEs (n= 337) were seen in all pts (71.5% grade [G] 1, 19.3% G2, 8.6% G3, 0.6% G4); the most common were leukopenia (7.7%), neutropenia (7.1%), anemia (5.9%). G3/4 TEAEs occurred in 19 pts (73.1%). Among the 19, incidence of G3/4 neutropenia was 50%, hypertension 26.9%, leucopenia 7.7%. TEAEs (hypertension, ventricular tachycardia, pulmonary edema) leading to treatment discontinuation were reported in 1 pt. Two pts had at least one SAE. No treatment-related deaths occurred. Pt reported outcomes using NCI PRO-CTCAE revealed no differences in appetite, nausea, respiratory symptoms, edema, palpitations, rashes and dry skin, or concentration from BL to end of C4. Pts had worsening hair loss from BL to end of C4. Ki67 analysis indicated CCCA in 78% at C1D15, compared to 18% at surgery after only P had been discontinued approximately 4 weeks prior to surgery. RNA sequencing was performed on available biopsies collected at BL (N=16), C1D15 (N=5), and surgery (N=2) from 16 pts. Among 16 BL samples, PAM50 subtyping identified 5 (31.3%) basal-like, 2 (12.5%) HER2-E, 6 (37.5%) Lum B, and 3 (18.8%) normal. Subtype switching to Lum A at C1D15 (N=3, 1 each with HER2-E, Lum B, and normal at BL) or normal (N=2, 1 basal and 1 HER2-E at BL) was observed. 161 genes were differentially expressed (FDR p<0.05); 145 downregulated and 16 upregulated comparing C1D15 to BL. MKI67, TK1, CCNB1, AURKB, PLK1 were among the downregulated genes, consistent with CCCA for majority of the samples at C1D15 by Ki67. Analysis of the Molecular Signatures Database Hallmark gene-sets comparing C1D15 and BL samples demonstrated downregulated biological processes involved in proliferation (E2F targets, G2M checkpoint, MYC targets, mitotic spindle), signaling (Estrogen response, mTORC1 signaling), and DNA damage (DNA repair) at C1D15, consistent with the mechanisms of action of the study drugs. E2F targets were higher in BL samples of RCB II/III, compared to RCB I (FDR p=0.042). Conclusions PALTAN did not meet its primary endpoint of pCR. Neoadjuvant PLT showed a pCR of 7.7% but was well tolerated. RNA sequencing and Ki67 data indicated potent anti-proliferative effects of study treatments, despite significant heterogeneity of intrinsic subtypes. Clinical trial information: NCT02907918. Citation Format: Foluso O Ademuyiwa, Donald Northfelt, Tracey O'Connor, Ellis Levine, Jingqin Luo, Yu Tao, Jeremy Hoog, Marie Laury, Tracy Summa, Trish Hammerschmidt, Zhanfang Guo, Ashley Frith, Katherine Weilbaecher, Mateusz Opyrchal, Rebecca Aft, Katherine Clifton, Rama Suresh, Nusayba Bagegni, Ian S Hagemann, Cynthia X Ma. Phase 2 study of neoadjuvant palbociclib, letrozole, and trastuzumab in patients with ER+ HER2+ breast cancer (PALTAN) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-01.

Abstract Purpose: Hyperactivation of AKT is common and associated with endocrine resistance in estrogen receptor–positive (ER+) breast cancer. The allosteric pan-AKT inhibitor MK-2206 induced apoptosis in PIK3CA-mutant ER+ breast cancer under estrogen-deprived condition in preclinical studies. This neoadjuvant phase II trial was therefore conducted to test the hypothesis that adding MK-2206 to anastrozole induces pathologic complete response (pCR) in PIK3CA mutant ER+ breast cancer. Experimental Design: Potential eligible patients with clinical stage II/III ER+/HER2− breast cancer were preregistered and received anastrozole (goserelin if premenopausal) for 28 days in cycle 0 pending tumor PIK3CA sequencing. Patients positive for PIK3CA mutation in the tumor were eligible to start MK-2206 (150 mg orally weekly, with prophylactic prednisone) on cycle 1 day 2 (C1D2) and to receive a maximum of four 28-day cycles of combination therapy before surgery. Serial biopsies were collected at preregistration, C1D1 and C1D17. Results: Fifty-one patients preregistered and 16 of 22 with PIK3CA-mutant tumors received study drug. Three patients went off study due to C1D17 Ki67 >10% (n = 2) and toxicity (n = 1). Thirteen patients completed neoadjuvant therapy followed by surgery. No pCRs were observed. Rash was common. MK-2206 did not further suppress cell proliferation and did not induce apoptosis on C1D17 biopsies. Although AKT phosphorylation was reduced, PRAS40 phosphorylation at C1D17 after MK-2206 persisted. One patient acquired an ESR1 mutation at surgery. Conclusions: MK-2206 is unlikely to add to the efficacy of anastrozole alone in PIK3CA-mutant ER+ breast cancer and should not be studied further in the target patient population. Clin Cancer Res; 23(22); 6823–32. ©2017 AACR.