A Food and Drug Administration analysis of survival outcomes comparing the Adjuvant Paclitaxel and Trastuzumab trial with an external control from historical clinical trials

BACKGROUND

Although the Adjuvant Paclitaxel and Trastuzumab (APT) trial has been adopted clinically, single-arm trials have limitations, and interest remains whether these patients with small node-negative human epidermal growth factor receptor 2 (HER2)-positive early breast cancer (EBC) would benefit from more intensive chemotherapy. This analysis explored whether external controls can contextualize single-arm studies to add to clinical decision making in the use of de-escalated therapy in patients with low-risk HER2-positive EBC.

PATIENTS AND METHODS

Patient-level data from five randomized trials supporting drug approval in adjuvant HER2-positive EBC were pooled, and patients with low-risk EBC were selected (n = 1770). Patients treated concurrently with trastuzumab and either anthracycline/cyclophosphamide/taxane/trastuzumab (ACTH) or taxane/carboplatin/trastuzumab (TCH; n = 1366) were matched (1:1) to patients treated with paclitaxel and trastuzumab (TH) in the APT trial (n = 406) using propensity scores. Patients treated with anthracycline/cyclophosphamide/taxane (ACT; n = 374) were also matched (1:1) to those treated with TH. Propensity scores were estimated using covariates of age, tumor stage, estrogen receptor status, progesterone receptor status, and histological grade.

RESULTS

After matching, the estimated probabilities of invasive disease-free survival (iDFS) at 3 and 5 years were 98.6% and 96.5% in the TH arm, and 96.6% and 92.9% in the ACTH/TCH arm, respectively. The estimated probabilities of overall survival (OS) at 3 and 5 years were 99.7% and 99.3% in the TH arm, and 99.0% and 97.4% in the ACTH/TCH arm, respectively. Comparing the TH arm with the ACT arm in the matched sample, the estimated difference in iDFS was 7.5% (TH 98.8% and ACT 91.3%) at 3 years and 12.6% (TH 96.1% and ACT 83.5%) at 5 years. The estimated difference in OS was 2.6% (TH 100% and ACT 97.4%) at 3 years, and 5.3% (TH 99.3% and ACT 94.0%) at 5 years.

CONCLUSIONS

Our analyses suggest that patients' outcomes in both arms were in general similar, thus providing additional reassurance regarding de-escalation of therapy.

Abstract P4-01-09: 18F-FLT-PET/CT for the prediction of response to ANG-1005 therapy in patients with brain metastases from breast cancer

Background: ANG1005 (formerly called GRN1005) is a peptide-drug conjugate being developed for targeted treatment of brain metastases. It consists of 3 molecules of paclitaxel covalently linked to Angiopep-2 designed to cross the blood brain barrier (BBB) via the low density lipoprotein (LDL) receptor-related protein-1 (LRP1)-mediated trancytosis. This drug was evaluated in a multi-center, open-label single-arm study (GRABMB study). An interim analysis determined that the agent met the futility endpoint based on MRI assessment (SABC 2012). However, centrally confirmed responses were achieved in the study, and a biomarker substudy enrolling patients (pts) to evaluate the utility of FLT-PET in assessing response to treatment with ANG1005 suggested sufficient activity of the agent to allow continuation of the study. 18F-FLT (3’-Fluoro-3’ deoxythymidine)-PET imaging is a novel imaging modality which provides a tool for measuring in vivo tumor cell proliferation. FLT is an analog of thymidine; cellular retention of FLT reflects DNA synthesis.

Methods: Adult pts with measurable BMBC were eligible with or without history of prior WBRT. We compared 18F-FLT-PET/CT with MRI-gadolinium contrast images for brain metastases detection and for assessment of whether treatment with ANG1005 was associated with significant change in intracranial tumor uptake of 18F-FLT.

ANG1005 therapy was administered intravenously at 550 mg/m2 q 21d until progression of intra-cranial disease or unacceptable toxicity. All pts underwent 18F-FLT PET/CT imaging before and after 1 cycle of therapy with ANG1005. Pts were scanned dynamically over 30 min followed by a static whole body PET image at 1 hour post-injection. We calculated the% of change before and after therapy, with change > 20% considered significant.

Results: 5/10 planned pts have been accrued to the substudy to date, and 12 metastatic brain lesions have been analyzed. The maximum standard uptake value (SUVmax) ranged from 0.8 to 4.0, mean 1.8 for baseline scans. Tumor to normal brain background ratios ranged from 3.2 to 22.3, mean 9.4. 7/12 lesions showed >20% change between pre and post therapy. The average% change was (-) 42.39% ± 12.77, range: 29.2 to 66.8% (using SUVmax), and (-) 38.7% ± 14.3, range: 20.12 to 57.10% (using tumor to normal ratios). Based on brain MRI evaluation per RECIST 1.1 criteria, 1 pt had intra-cranial partial response (PR) and 3 patients had stable disease (SD). These pts remained on therapy for an average of 7 cycles, range: 5 to 9 cycles. 1 pt withdrew consent after 2 cycles of therapy and opted to receive whole brain radiation therapy. 5/42 pts achieved a confirmed investigator-assessed PR by MRI at 550 mg/m2, and 4/13 pts achieved a PR at 650 mg/m2, a dose not progressed due to toxicity.

Conclusion: This pilot study using 18F-FLT-PET imaging of brain metastases suggests that it is a promising tool for detection and measurement of CNS disease. Given that contrast-enhanced MRI detection of brain metastases represent gadolinium leakage through the BBB rather than actual tumor volume measurements, better approaches are needed to assess efficacy of therapies. Accrual to this study is ongoing. Updated results with ANG1005 will be presented during the meeting.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-09.

Determining the rate of tumor growth and decay in patients with metastatic breast cancer as an early efficacy endpoint: A study assessing ixabepilone efficacy

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Background: Early efficacy assessment in drug development should help find new cancer therapies. We have developed a novel method to analyze tumor response to therapy by quantifying the rate of tumor regression (d) and growth (g). We have shown g is slower when pts are on effective therapy and that g correlates with survival (Stein et al, Oncologist 2008). We utilized this method to evaluate a phase III trial of capecitabine (CAP) ± IXA in second line therapy (Tomas et al, JCO 2007) and a three-cohort phase II trial in second and subsequent lines of therapy in pts with MBC consisting of (1) Daily X 5 IXA given to taxane (TAX)-naïve patients (Denduluri et al, JCO 2007); (2) Daily X 5 IXA in pts previously treated with TAX (Low et al, JCO 2005); and (3) Daily X 3 IXA in pts previously treated with TAX (Denduluri et al, Invest New Drug 2007).

Methods: Using tumor measurements assessed by RECIST and a two-phase mathematical equation we determined d and g.

Results: In the phase III study g was superior to PFS identifying a significant difference between the arms very early—before the 200th pt had enrolled. In an individual patient the g values could be estimated as early as the 3rd evaluation, long before tumor growth was observed clinically. IXA + CAP in second line (g = 0.0018) was more effective than CAP (g = 0.0023) at reducing g, and more effective (p=0.0085) than single agent IXA in the Phase II study (g = 0.0027). Single agent IXA was comparably effective (p=0.814) in reducing the g of tumors previously exposed to a TAX (g = 0.0032) as in reducing the g of TAX-naïve tumors (g = 0.0035), consistent with its development as an agent active in TAX-refractory disease. Unlike differences in g, the d of single agent IXA (0.118) was comparable to that of IXA+CAP (0.0074) suggesting differences were primarily driven by effect on the growth of residual tumor.

Conclusions: Unlike PFS, an incremental measure of efficacy, g is a continuous variable and can more accurately assess differences between treatments. Because calculations of g are indifferent to assessment intervals, estimating a tumor’s g allows comparison of efficacy across trials.