How we treat HER2-positive brain metastases.

Overexpression of the human epidermal growth factor 2 (HER2)/neu glycoprotein receptor in breast cancer is associated with increased risk of brain metastases, especially in patients with advanced disease. Improvements in the treatment of HER2-positive breast cancer has led to prolonged survival of patients with advanced disease, but the prevention and management of central nervous system metastases still poses unique clinical challenges given the associated morbidity and mortality of this site of disease. HER2-positive brain metastases are treated with surgery, radiation (stereotactic radiosurgery or whole brain radiotherapy), and systemic therapies, and are best managed by an experienced multidisciplinary team. The present article aims to provide an overview to our approach to treatment of HER2-positive brain metastases, including a review of agents with central nervous system activity, as well as management suggestions for several nuanced clinical scenarios.

Phase I dose-escalation trial of tucatinib in combination with trastuzumab in patients with HER2-positive breast cancer brain metastases.

BACKGROUND: Brain metastases are frequent in HER2-positive breast cancer. ONT-380 (tucatinib) is a potent selective inhibitor of HER2 with intracranial activity in preclinical models. PATIENTS AND METHODS: This was a phase I study of tucatinib with trastuzumab, without chemotherapy, in patients with progressive, measurable HER2-positive brain metastases. The study tested two schedules of tucatinib: cohort A was twice daily and cohort B was once daily. The primary objective was determination of the maximum tolerated dose (MTD). Secondary end points included objective response (intracranial and extracranial) using modified RECIST and clinical benefit rate (CBR). RESULTS: Overall, 41 patients were enrolled (cohort A, n = 22; cohort B, n = 19). Patients had a median of two prior treatments for metastatic breast cancer and 83% had progressed after prior brain radiation. The MTD of tucatinib for cohort A was 300 mg twice daily and for cohort B was 750 mg once daily. The most common dose-limiting toxicities included thrombocytopenia and aspartate transaminase/alanine aminotransferase elevation. Grade 3/4 aspartate transaminase/alanine aminotransferase elevation occurred in nine of 41 patients (22%). Intracranial responses were observed in two of 17 (12%) patients in cohort A and one of 17 (6%) patients in cohort B treated at the MTD. In cohort A, CBR at 16 weeks was 35% (n = 6). In cohort B, CBR at 16 weeks was 53% (n = 9). Of 15 patients overall who experienced clinical benefit, 12 (80%) had received prior neratinib and/or lapatinib. Median progression-free survival for cohorts A and B was 3.4 and 4.1 months, respectively. CONCLUSION: The combination of tucatinib and trastuzumab is tolerable and demonstrated preliminary evidence of efficacy in patients with HER2-positive brain metastases. CLINICAL TRIAL REGISTRATION: NCT01921335.

Reversion and non-reversion mechanisms of resistance to PARP inhibitor or platinum chemotherapy in BRCA1/2-mutant metastatic breast cancer.

BACKGROUND: Little is known about mechanisms of resistance to poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPi) and platinum chemotherapy in patients with metastatic breast cancer and BRCA1/2 mutations. Further investigation of resistance in clinical cohorts may point to strategies to prevent or overcome treatment failure. PATIENTS AND METHODS: We obtained tumor biopsies from metastatic breast cancer patients with BRCA1/2 deficiency before and after acquired resistance to PARPi or platinum chemotherapy. Whole exome sequencing was carried out on each tumor, germline DNA, and circulating tumor DNA. Tumors underwent RNA sequencing, and immunohistochemical staining for RAD51 foci on tumor sections was carried out for functional assessment of intact homologous recombination (HR). RESULTS: Pre- and post-resistance tumor samples were sequenced from eight patients (four with BRCA1 and four with BRCA2 mutation; four treated with PARPi and four with platinum). Following disease progression on DNA-damaging therapy, four patients (50%) acquired at least one somatic reversion alteration likely to result in functional BRCA1/2 protein detected by tumor or circulating tumor DNA sequencing. Two patients with germline BRCA1 deficiency acquired genomic alterations anticipated to restore HR through increased DNA end resection: loss of TP53BP1 in one patient and amplification of MRE11A in another. RAD51 foci were acquired post-resistance in all patients with genomic reversion, consistent with reconstitution of HR. All patients whose tumors demonstrated RAD51 foci post-resistance were intrinsically resistant to subsequent lines of DNA-damaging therapy. CONCLUSIONS: Genomic reversion in BRCA1/2 was the most commonly observed mechanism of resistance, occurring in four of eight patients. Novel sequence alterations leading to increased DNA end resection were seen in two patients, and may be targetable for therapeutic benefit. The presence of RAD51 foci by immunohistochemistry was consistent with BRCA1/2 protein functional status from genomic data and predicted response to later DNA-damaging therapy, supporting RAD51 focus formation as a clinically useful biomarker.

PIK3CA(H1047R)- and Her2-initiated mammary tumors escape PI3K dependency by compensatory activation of MEK-ERK signaling.

Human breast cancers that have HER2 amplification/overexpression frequently carry PIK3CA mutations, and are often associated with a worse prognosis. However, the role of PIK3CA mutations in the initiation and maintenance of these breast cancers remains elusive. In the present study, we generated a compound mouse model that genetically mimics HER2-positive breast cancer with coexisting PIK3CA(H1047R). Induction of PIK3CA(H1047R) expression in mouse mammary glands with constitutive expression of activated Her2/Neu resulted in accelerated mammary tumorigenesis with enhanced metastatic potential. Interestingly, inducible expression of mutant PIK3CA resulted in a robust activation of phosphatidylinositol-3-kinase (PI3K)/AKT signaling but attenuation of Her2/Her3 signaling, and this can be reversed by deinduction of PIK3CA(H1047R) expression. Strikingly, although these Her2(+) PIK3CA(H1047R)-initiated primary mammary tumors are refractory to HER2-targeted therapy, all tumors responded to inactivation of the oncogenic PIK3CA(H1047R), a situation closely mimicking the use of a highly effective inhibitor specifically targeting the mutant PIK3CA/p110a. Notably, these tumors eventually resumed growth, and a fraction of them escaped PI3K dependence by compensatory ERK activation, which can be blocked by combined inhibition of Her2 and MEK. Together, these results suggest that PIK3CA-specific inhibition as a monotherapy followed by combination therapy targeting MAPK and HER2 in a timely manner may be an effective treatment approach against HER2-positive cancers with coexisting PIK3CA-activating mutations.

PI3K-p110α mediates resistance to HER2-targeted therapy in HER2+, PTEN-deficient breast cancers.

Human epidermal growth factor receptor-2 (HER2) amplification/overexpression (HER2+) frequently co-occurs with PI3K pathway activation in breast tumors. PI3K signaling is most often activated by PIK3CA mutation or PTEN loss, which frequently results in sensitivity to p110α or p110ß inhibitors, respectively. To examine the p110 isoform dependence in HER2+, PTEN-deficient tumors, we generated genetic mouse models of breast tumors driven by concurrent Her2 activation and Pten loss coupled with deletion of p110α or p110ß. Ablation of p110α, but not p110ß, significantly impaired the development of Her2+/Pten-null tumors in mice. We further show that p110α primarily mediates oncogenic signaling in HER2+/PTEN-deficient human cancers while p110ß conditionally mediates PI3K/AKT signaling only upon HER2 inhibition. Combined HER2 and p110α inhibition effectively reduced PI3K/AKT signaling and growth of cancer cells both in vitro and in vivo. Addition of the p110ß inhibitor to dual HER2 and p110α inhibition induced tumor regression in a xenograft model of HER2+/PTEN-deficient human cancers. Together, our data suggest that combined inhibition of HER2 and p110α/ß may serve as a potent and durable therapeutic regimen for the treatment of HER2+, PTEN-deficient breast tumors.

Trastuzumab emtansine (T-DM1) versus lapatinib plus capecitabine in patients with HER2-positive metastatic breast cancer and central nervous system metastases: a retrospective, exploratory analysis in EMILIA.

BACKGROUND: We characterized the incidence of central nervous system (CNS) metastases after treatment with trastuzumab emtansine (T-DM1) versus capecitabine-lapatinib (XL), and treatment efficacy among patients with pre-existing CNS metastases in the phase III EMILIA study. PATIENTS AND METHODS: In EMILIA, patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer previously treated with trastuzumab and a taxane were randomized to T-DM1 or XL until disease progression. Patients with treated, asymptomatic CNS metastases at baseline and patients developing postbaseline CNS metastases were identified retrospectively by independent review; exploratory analyses were carried out. RESULTS: Among 991 randomized patients (T-DM1 = 495; XL = 496), 95 (T-DM1 = 45; XL = 50) had CNS metastases at baseline. CNS progression occurred in 9 of 450 (2.0%) and 3 of 446 (0.7%) patients without CNS metastases at baseline in the T-DM1 and XL arms, respectively, and in 10 of 45 (22.2%) and 8 of 50 (16.0%) patients with CNS metastases at baseline. Among patients with CNS metastases at baseline, a significant improvement in overall survival (OS) was observed in the T-DM1 arm compared with the XL arm [hazard ratio (HR) = 0.38; P = 0.008; median, 26.8 versus 12.9 months]. Progression-free survival by independent review was similar in the two treatment arms (HR = 1.00; P = 1.000; median, 5.9 versus 5.7 months). Multivariate analyses demonstrated similar results. Grade ≥3 adverse events were reported in 48.8% and 63.3% of patients with CNS metastases at baseline administered T-DM1 and XL, respectively; no new safety signals were observed. CONCLUSION: In this retrospective, exploratory analysis, the rate of CNS progression in patients with HER2-positive advanced breast cancer was similar for T-DM1 and for XL, and higher overall in patients with CNS metastases at baseline compared with those without CNS metastases at baseline. In patients with treated, asymptomatic CNS metastases at baseline, T-DM1 was associated with significantly improved OS compared with XL.

A phase II study of bevacizumab in combination with vinorelbine and trastuzumab in HER2-positive metastatic breast cancer.

We aimed to evaluate the efficacy and feasibility of combining trastuzumab/vinorelbine with bevacizumab in patients with first-or second-line HER2-positive, metastatic breast cancer (MBC). Eligible patients had HER2-positive measureable MBC, with no more than one prior line of chemotherapy, and were treated with trastuzumab (4 mg/kg × 2 mg/kg weekly thereafter), vinorelbine (25 mg/m(2) weekly), and bevacizumab (10 mg/kg every 2 weeks). Co-primary endpoints were (a) the proportion of patients alive and progression-free at 1 year and (b) safety profile/feasibility. Feasibility was defined as a rate of grade 3/4 non-hematologic toxicity attributable to protocol-based therapy <20 %. Twenty-nine patients were enrolled (n = 22 first-line, n = 7 second-line). Median age was 48 years (range 37-68). The median number of cycles received was 8 (1-23) and median duration on treatment was 7.4 months (range 1-22). The study was closed early due to higher-than-expected rates of grade 3/4 non-hematologic toxicities, with 50 events in 20 patients. A total of six patients (21 %) were taken off study for treatment-related toxicity. Most common treatment-related toxicities included fatigue (n = 7), febrile neutropenia (n = 4), and headache (n = 3). At 1 year, 8/22 first-line (36 %) and 2/7 second-line (29 %) patients were alive and progression-free. Median PFS was 9.9 months and 7.8 months in the first- and second-line cohorts, respectively. Objective responses were observed in 16/22 (73 %) and 5/7 (71 %) patients in the first- and second-line settings. Although the combination of vinorelbine, trastuzumab, and bevacizumab showed notable activity in HER2-positive MBC, the proportion of first-line patients alive and progression-free at 1 year was deemed unlikely to reach the pre-defined threshold for declaring success. Additionally, unacceptable toxicity was observed, at rates greater than previously reported with vinorelbine/trastuzumab or vinorelbine/bevacizumab doublet combinations.

Incidence and risk of central nervous system metastases as site of first recurrence in patients with HER2-positive breast cancer treated with adjuvant trastuzumab.

BACKGROUND: Central nervous system (CNS) disease as the site of first relapse after exposure to adjuvant trastuzumab has been reported. We carried out comprehensive meta-analysis to determine the risk of CNS metastases as the first site of recurrence in patients with HER2-positive breast cancer who received adjuvant trastuzumab. METHODS: Eligible studies include randomized trials of adjuvant trastuzumab administered for 1 year to patients with HER2-positive breast cancer who reported CNS metastases as first site of disease recurrence. Statistical analyses were conducted to calculate the incidence, relative risk (RR), and 95% confidence intervals (CIs) using fixed-effects inverse variance and random-effects models. RESULTS: A total of 9020 patients were included. The incidence of CNS metastases as first site of disease recurrence in HER2-positive patients receiving adjuvant trastuzumab was 2.56% (95% CI 2.07% to 3.01%) compared with 1.94% (95% CI 1.54% to 2.38%) in HER2-positive patients who did not receive adjuvant trastuzumab. The RR of the CNS as first site of relapse in trastuzumab-treated patients was 1.35 (95% CI 1.02-1.78, P = 0.038) compared with control arms without trastuzumab therapy. The ratio of CNS metastases to total number of recurrence events was 16.94% (95% CI 10.85% to 24.07%) and 8.33% (95% CI 6.49% to 10.86%) for the trastuzumab-treated and control groups, respectively. No statistically significant differences were found based on trastuzumab schedule or median follow-up time. No evidence of publication bias was observed. CONCLUSIONS: Adjuvant trastuzumab is associated with a significant increased risk of CNS metastases as the site of first recurrence in HER2-positive breast cancer patients.

Human epidermal growth factor receptor-2-positive breast cancer: does estrogen receptor status define two distinct subtypes?

BACKGROUND: Human epidermal growth factor receptor-2 (HER2) overexpression occurs in ∼20% of breast cancers and has historically been associated with decreased survival. Despite substantial improvements in clinical outcomes, particularly with the emergence of HER2-targeted therapy, a substantial minority of patients still relapses, and progression is inevitable in metastatic disease. Accumulating data indicate that HER2-positive disease is itself a heterogeneous entity. METHODS AND RESULTS: In this article, we qualitatively review the data supporting the classification of HER2-positive disease as at least two separate entities, distinguished by estrogen receptor (ER) status. We summarize differences in clinical outcomes, including response to neoadjuvant therapy, timing and patterns of dissemination, efficacy of therapy in the metastatic setting and survival outcomes. CONCLUSIONS: The collective data are sufficiently strong at this point to propose that ER status defines two distinct subtypes within HER2-positive breast cancer, and we highlight the implications of this knowledge in future research, including understanding of the basic biology of HER2-positive breast cancer and the design of future clinical trials.

Inhibiting HSP90 to treat cancer: a strategy in evolution.

Since the identification of the first HSP90 inhibitor almost two decades ago, there has been substantial progress made in the development of potent and selective molecules that inhibit this chaperone and that have anticancer activity. In turn, these compounds have been invaluable for probing how HSP90 supports the profound changes in cellular physiology that characterize the malignant state. Unfortunately, when used as single agents HSP90 inhibitors have demonstrated disappointing activity against advanced cancers in most of the clinical trials reported to date. This problem may be due to the major pharmacological liabilities of the first-generation HSP90 inhibitors that have been most extensively studied. We suggest, however, that it may well be intrinsic to the target itself. Systemically tolerable exposure to HSP90 inhibitors may not be highly cytotoxic for the majority of common clinical cancers. Instead, HSP90 inhibitors might better be used to enhance the activity of other antineoplastic agents while simultaneously reducing the capacity of tumors to adapt and evolve drug resistance; the overall result being more durable disease control. This review will focus on these fundamental issues with the goal of suggesting ways to make the clinical development of HSP90 inhibitors become less empiric and ultimately more successful.

Responses to subsequent anti-HER2 therapy after treatment with trastuzumab-DM1 in women with HER2-positive metastatic breast cancer.

BACKGROUND: Women with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC) can respond to multiple lines of anti-HER2 therapy. It is unknown whether these patients will derive further clinical benefit following treatment with trastuzumab-MCC-DM1 (T-DM1). PATIENTS AND METHODS: We retrospectively identified HER2-positive MBC patients treated with T-DM1 and characterized outcomes during subsequent lines of anti-HER2 therapy. Response was determined by a blinded radiology review. Time-dependent analyses were carried out using Kaplan-Meier estimates. RESULTS: We identified 23 patients treated with single-agent T-DM1 and report on the 20 patients who discontinued protocol therapy. All patients received trastuzumab-based metastatic therapy before initiation of T-DM1 [median 7 regimens (range 3-14)]. Of these 20 patients, 75% (15 of 20) received further therapy with or without anti-HER2 agents after discontinuing T-DM1. Partial response to either first- or second-subsequent line(s) of therapy was seen in 5 of 15 (33%) treated patients, including 33% (4 of 12) who received a regimen containing trastuzumab and/or lapatinib. Median durations of therapy to first- and second-subsequent regimens after T-DM1 were 5.5 and 6.4 months, respectively. CONCLUSIONS: In heavily pretreated HER2-positive MBC patients, prior exposure to T-DM1 does not exhaust the potential benefit of ongoing anti-HER2 therapy with trastuzumab- and/or lapatinib-based regimens.

A novel mutation in the deoxyribonucleic acid-binding domain of the vitamin D receptor causes hereditary 1,25-dihydroxyvitamin D-resistant rickets.

Mutations in the vitamin D receptor (VDR) result in hereditary 1,25-dihydroxyvitamin D3-resistant rickets (HVDRR), an autosomal recessive disease caused by target organ resistance to the action of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. In this study, we investigated the molecular basis of HVDRR in a child from Saudi Arabia who was previously shown to be resistant to 1,25-(OH)2D3 action, but whose cultured skin fibroblasts exhibited normal [3H]1,25-(OH)2D3 binding. Using the PCR, exons 2 and 3 of the VDR gene that encode the DNA-binding region of the receptor were amplified and sequenced. A novel point mutation at nucleotide 252 in exon 2 of the VDR was identified. This missense mutation (GGC to GAC) resulted in the conversion of glycine to aspartic acid at amino acid position 46 (G46D), located at the base of the first zinc finger. This single base change was introduced into wild-type VDR complementary DNA by site-directed mutagenesis, and the mutant VDR was then expressed in COS-1 cells. The expressed mutant VDR displayed a normal binding affinity (Kd = 1.2 x 10(-10) mol/L) for [3H]1,25-(OH)2D3 as determined by Scatchard analysis. However, the mutant VDR was shown to have reduced binding affinity for DNA by DNA-cellulose chromatography. In COS-7 cells cotransfected with a vitamin D response element-chloramphenicol acetyltransferase reporter construct and the mutant VDR complementary DNA expression vector, the mutant VDR was unable to activate gene transcription in cells treated with up to 100 nmol/L 1,25-(OH)2D3. Restriction fragment length polymorphism analysis using MwoI restriction digests of exon 2 demonstrated that the affected child is homozygous for the mutation, whereas the child's father is heterozygous and a carrier of the defective allele. In conclusion, a new mutation was identified in exon 2 of the VDR gene. This mutation, which occurs in the first zinc finger of the DNA-binding domain of the receptor, blocks 1,25-(OH)2D3 action and leads to the syndrome of HVDRR.