Abstract P3-07-58: CD44v as a potential predictive biomarker for pathologic complete response in primary HER2+ breast cancer: Utility of adaptive response biopsy in preoperative therapy

Abstract

Abstract Background: Preoperative dual anti-HER2 therapy with lapatinib and trastuzumab in combination with conventional chemotherapy demonstrates a higher pathologic complete response rate (pCR) than trastuzumab with chemotherapy in patients with HER2+ breast cancer. Preoperative chemotherapy has been reported to increase the fraction of cancer stem-like cells (CSCs) in breast cancer, but this effect has not been well validated in clinical setting. Cancer cells with the epithelial-mesenchymal transition (EMT) phenotype also exhibit stem cell–like properties with drug resistance. Our goal was to determine the quantitative values of various biomarkers in baseline and adaptive response biopsy specimens and in subsequent surgical specimens to predict pCR in patients treated with dual anti-HER2 therapy as demonstrated by reduction of CSCs, phosphorylated receptors and signaling kinases, and circulating tumor cells (CTC) with the EMT phenotype. Methods: Eighteen patients with operable primary HER2+ invasive breast cancer (≥T2 excluding inflammatory breast cancer, any N) were eligible. Patients received lapatinib (1000 mg PO daily) + trastuzumab (4 mg/kg at loading, then 2 mg/kg IV weekly) for the first 6 weeks, then lapatinib (750 mg daily) + trastuzumab (2 mg/kg IV weekly) + paclitaxel (80 mg/m2 IV weekly) for 12 weeks, followed by surgery (ClinicalTrials.gov Identifier: NCT01688609). Tumor and blood specimens were collected before (baseline), after the 6 weeks of dual anti-HER2 therapy (adaptive response biopsy), and at 18 weeks, after 12 weeks of dual anti-HER2 therapy + paclitaxel (surgical specimens). We measured CSC biomarkers CD44 variant (CD44v) and aldehyde dehydrogenase-1 in tumor tissues, EMT markers in CTCs (TWIST1, SNAIL1, SLUG, ZEB1, and FOXC2) in blood samples by quantitative RT-PCR, and the ratios of phosphorylated EGFR (pEGFR)/EGFR, pHER2/HER2, pERK/ERK, and pAkt/Akt in tumor tissues. All tissue and CTC biomarker levels at all three time points were evaluated for their association with response via Fisher's exact test, McNemar's test, and Wilcoxon rank sum test according to the variables. Results: Eight of 18 patients (44.4%) achieved pCR after dual anti-HER2 therapy + concurrent paclitaxel. All patients who achieved pCR showed reduction or disappearance of CD44v+ cells over the treatment course. Five of the 10 non-pCR patients showed consistent CD44v expression or enrichment after dual anti-HER2 therapy in both the adaptive response biopsy and the surgical specimens. None of the eight pCR patients had detectable CD44v in the 7-week adaptive response biopsy specimen (Fisher exact test, two-tailed, P = 0.0359). None of the other markers significantly predicted pCR. Conclusion: Persistent expression or enrichment of CD44v was suggested to be predictive for non-pCR in breast cancer patients treated with preoperative dual anti-HER2 therapy plus concurrent cytotoxic chemotherapy. A single evaluation of biomarkers before therapy is insufficient for prediction of clinical response. Application of the adaptive response biopsy during the course of preoperative therapy might play a significant role in the success of therapeutic strategies that target CSCs. Citation Format: Yamauchi T, Imamura CK, Yamauchi H, Jinno H, Takahashi M, Kitagawa Y, Nakamura S, Lim B, Krishnamurthy S, Reuben JM, Liu D, Tripathy D, Zujewski JA, Chen H, Takebe N, Saya H, Ueno NT. CD44v as a potential predictive biomarker for pathologic complete response in primary HER2+ breast cancer: Utility of adaptive response biopsy in preoperative therapy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-58.