Mary Ellen Moynahan

Brca1 Controls Homology-Directed DNA Repair

Germline mutations in BRCA1 confer a high risk of breast and ovarian tumors. The role of BRCA1 in tumor suppression is not yet understood, but both transcription and repair functions have been ascribed. Evidence that BRCA1 is involved in DNA repair stems from its association with RAD51, a homolog of the yeast protein involved in the repair of DNA double-strand breaks (DSBs) by homologous recombination. We report here that Brca1-deficient mouse embryonic stem cells have impaired repair of chromosomal DSBs by homologous recombination. The relative frequencies of homologous and nonhomologous DNA integration and DSB repair were also altered. The results demonstrate a caretaker role for BRCA1 in preserving genomic integrity by promoting homologous recombination and limiting mutagenic nonhomologous repair processes.

BRCA2 is required for homology-directed repair of chromosomal breaks.

The BRCA2 tumor suppressor has been implicated in the maintenance of chromosomal stability through a function in DNA repair. In this report, we examine human and mouse cell lines containing different BRCA2 mutations for their ability to repair chromosomal breaks by homologous recombination. Using the I-SceI endonuclease to introduce a double-strand break at a specific chromosomal locus, we find that BRCA2 mutant cell lines are recombination deficient, such that homology-directed repair is reduced 6- to >100-fold, depending on the cell line. Thus, BRCA2 is essential for efficient homology-directed repair, presumably in conjunction with the Rad51 recombinase. We propose that impaired homology-directed repair caused by BRCA2 deficiency leads to chromosomal instability and, possibly, tumorigenesis, through lack of repair or misrepair of DNA damage.

Mitotic homologous recombination maintains genomic stability and suppresses tumorigenesis

Mitotic homologous recombination promotes genome stability through the precise repair of DNA double-strand breaks and other lesions that are encountered during normal cellular metabolism and from exogenous insults. As a result, homologous recombination repair is essential during proliferative stages in development and during somatic cell renewal in adults to protect against cell death and mutagenic outcomes from DNA damage. Mutations in mammalian genes encoding homologous recombination proteins, including BRCA1, BRCA2 and PALB2, are associated with developmental abnormalities and tumorigenesis. Recent advances have provided a clearer understanding of the connections between these proteins and of the key steps of homologous recombination and DNA strand exchange.

Weekly Trastuzumab and Paclitaxel Therapy for Metastatic Breast Cancer With Analysis of Efficacy by HER2 Immunophenotype and Gene Amplification

PURPOSE This phase II study evaluated weekly trastuzumab and paclitaxel therapy in women with HER2-normal and HER2-overexpressing metastatic breast cancer. Efficacy was correlated with immunohistochemical and fluorescent in situ hybridization (FISH) assay results. PATIENTS AND METHODS Eligible patients had bidimensionally measurable metastatic breast cancer. Up to three prior chemotherapy regimens, including prior anthracycline and taxane therapy, were allowed. Trastuzumab 4 mg/kg and paclitaxel 90 mg/m2 were administered on week 1, with trastuzumab 2 mg/kg and paclitaxel 90 mg/m2 administered on subsequent weeks. HER2 status was evaluated using four different immunohistochemical assays and FISH. RESULTS Patients received a median of 25 weekly infusions (range, one to 85 infusions). Median delivered paclitaxel dose-intensity was 82 mg/m2/wk (range, 52 to 90 mg/m2/wk). The intent-to-treat response rate for all 95 patients enrolled was 56.8% (95% confidence interval, 47% to 67%). A response rate of 61.4% (4.5% complete response, 56.8% partial response) was observed in 88 fully assessable patients. In patients with HER2-overexpressing tumors, overall response rates ranged from 67% to 81% compared with 41% to 46% in patients with HER2-normal expression (ranges reflect the different assay methods used to assess HER2 status). Differences in response rates between patients with HER2-overexpressing tumors and those with normal HER2 expression were statistically significant for all assay methods, with CB11 and TAB250 antibodies and FISH having the strongest significance. Therapy was generally well tolerated, although three patients had serious cardiac complications. CONCLUSION Weekly trastuzumab and paclitaxel therapy is active in women with metastatic breast cancer. Therapy was relatively well tolerated; however, attention to cardiac function is necessary.

Dose-dense therapy with weekly 1-hour paclitaxel infusions in the treatment of metastatic breast cancer.

PURPOSE To evaluate the efficacy and toxicity of paclitaxel administered as a 1-hour infusion on weekly basis, without interruption, to patients with metastatic breast cancer who had received prior therapy. PATIENTS AND METHODS Thirty patients with metastatic breast cancer received sustained weekly paclitaxel therapy at an initial dose of 100 mg/m2 until disease progression. Prior therapy included adjuvant only (n=17), metastatic only (n=7), or both (n=6). Eighteen patients had received prior anthracycline therapy, 12 of whom had demonstrated progression of disease within 12 months of it. All patients were assessable for efficacy; 29 patients were assessable for toxicity. Pharmacokinetic studies of paclitaxel were also performed. RESULTS A total of 469 weekly paclitaxel infusions were administered to 30 patients (median, 14 infusions/patient). The median delivered dose-intensity was 91 mg/m2/wk (range, 80 to 108). The overall response rate was 53% (95% confidence interval [CI], 34% to 72%), with 10% complete responses (CRs) and 43% partial responses (PRs). Median response duration was 7.5 months (range, 2 to 11+). Responses were observed in nine of 18 (50%) patients with prior anthracycline therapy, including six of 12 (50%) with disease progression on anthracycline within 1 year (three of four within 6 months). Therapy was well tolerated and remarkable for a lack of overall and cumulative myelosuppression. Grade 3/4 neutropenia occurred in four patients; febrile neutropenia was not observed. Peripheral neuropathy prohibited dose escalation above 100 mg/m2, and grade 3 neuropathy was observed in two of 21 patients at < or = 100 mg/m2. CONCLUSION Weekly paclitaxel therapy is active and well tolerated in patients with metastatic breast cancer. Weekly therapy should be considered as a current clinical option for these patients and should be incorporated into future comparative clinical trials.

HSP90 Inhibition Is Effective in Breast Cancer: A Phase II Trial of Tanespimycin (17-AAG) Plus Trastuzumab in Patients with HER2-Positive Metastatic Breast Cancer Progressing on Trastuzumab

Purpose: HSP90 is a chaperone protein required for the stability of a variety of client proteins. 17-Demethoxygeldanamycin (17-AAG) is a natural product that binds to HSP90 and inhibits its activity, thereby inducing the degradation of these clients. In preclinical studies, HER2 is one of the most sensitive known client proteins of 17-AAG. On the basis of these data and activity in a phase I study, we conducted a phase II study of 17-AAG (tanespimycin) with trastuzumab in advanced trastuzumab-refractory HER2-positive breast cancer. Experimental Design: We enrolled patients with metastatic HER2+ breast cancer whose disease had previously progressed on trastuzumab. All patients received weekly treatment with tanespimycin at 450 mg/m2 intravenously and trastuzumab at a conventional dose. Therapy was continued until disease progression. The primary endpoint was response rate by Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Results: Thirty-one patients were enrolled with a median age of 53 years and a median Karnofsky performance status (KPS) of 90%. The most common toxicities, largely grade 1, were diarrhea, fatigue, nausea, and headache. The overall response rate was 22%, the clinical benefit rate [complete response + partial response + stable disease] was 59%, the median progression-free survival was 6 months (95% CI: 4–9), and the median overall survival was 17 months (95% CI: 16–28). Conclusions: This is the first phase II study to definitively show RECIST-defined responses for 17-AAG in solid tumors. Tanespimycin plus trastuzumab has significant anticancer activity in patients with HER2-positive, metastatic breast cancer previously progressing on trastuzumab. Further research exploring this therapeutic interaction and the activity of HSP90 inhibitors is clearly warranted. Clin Cancer Res; 17(15); 5132–9. ©2011 AACR.

PIK3CA mutation associates with improved outcome in breast cancer.

Purpose: In breast cancer, somatic mutations in the PIK3CA gene are common. The prognostic implication of these activating mutations remains uncertain as moderately sized studies have yielded variable outcomes. Our aim was to determine the prognostic implications of PIK3CA mutations in breast cancer. Experimental Design: Archival formalin-fixed paraffin-embedded primary breast tumors, from 590 patients selected for known vital status with a median follow-up of 12.8 years and a tumor >1 cm, were genotyped for PIK3CA mutations. Mutation rates and associations between mutation site and clinicopathologic characteristics were assessed. Progression-free survival, overall survival, and breast cancer–specific survival were examined using Kaplan-Meier or competing risk methodology. Results: PIK3CA mutation is identified in 32.5% of breast cancers. PIK3CA mutation significantly associates with older age at diagnosis, hormone receptor positivity, HER2 negativity, lower tumor grade and stage, and lymph node negativity. Patients with PIK3CA mutated tumors have significant improvement in overall survival (P = 0.03) and breast cancer–specific survival (P = 0.004). Analysis for PIK3CA mutation site-specific associations reveals that the H1047R kinase domain mutation highly associates with node negativity (P = 0.007), whereas helical domain hotspot mutations associate with older age at diagnosis (P = 0.004). Conclusion: This study defines the positive prognostic significance of PIK3CA mutations. This work is clinically relevant, as it will significantly affect the design of clinical trials planned for phosphatidylinositol 3-kinase–targeted therapy. Future work may define a population of older age breast cancer patients in whom therapy can be minimized. (Clin Cancer Res 2009;15(16):5049–59)

Phase II trial of bicalutamide in patients with androgen receptor-positive, estrogen receptor-negative metastatic breast cancer

Purpose: Patients with hormone receptor–negative breast cancer generally do not benefit from endocrine-targeted therapies. However, a subset with androgen receptor (AR) expression is predicted to respond to antiandrogen therapies. This phase II study explored bicalutamide in AR-positive, estrogen receptor (ER), and progesterone receptor (PgR)-negative metastatic breast cancer. Experimental Design: Tumors from patients with ER/PgR-negative advanced breast cancer were tested centrally for AR [immunohistochemistry (IHC) > 10% nuclear staining considered positive]. If either the primary or a metastatic site was positive, patients were eligible to receive the AR antagonist bicalutamide at a dose of 150 mg daily. Clinical benefit rate (CBR), the primary endpoint, was defined as the total number of patients who show a complete response (CR), partial response (PR), or stable disease (SD) > 6 months; secondary endpoints included progression-free survival (PFS) and toxicity. Correlative studies included measurement of circulating endocrine markers and IHC surrogates for basal-like breast cancer. Results: Of 424 patients with ER/PgR-negative breast cancer, 12% tested AR-positive. The 6-month CBR was 19% [95% confidence interval (CI), 7%–39%] for bicalutamide. The median PFS was 12 weeks (95% CI, 11–22 weeks). Bicalutamide was well-tolerated with no grade 4/5 treatment-related adverse events observed. Conclusion: AR was expressed in 12% of patients with ER/PgR-negative breast cancer screened for this trial. The CBR of 19% observed with bicalutamide shows proof of principle for the efficacy of minimally toxic androgen blockade in a select group of patients with ER/PgR-negative, AR-positive breast cancer. Clin Cancer Res; 19(19); 5505–12. ©2013 AACR.

Double-strand breaks and tumorigenesis

The establishment of connections between biochemical defects and clinical disease is a major goal of modern molecular genetics. In this review, we examine the current literature that relates defects in the two major DNA double-strand-break repair pathways--homologous recombination and nonhomologous end-joining--with the development of human tumors. Although definitive proof has yet to be obtained, the current literature is highly suggestive of such a link.

Breast Cancer Methylomes Establish an Epigenomic Foundation for Metastasis

Breast cancer methylomes contribute to metastatic potential, modulate the metastasis transcriptome, and predict disease outcome. Meditating on Breast Cancer People of diverse faiths and backgrounds have gained new mindsets when contemplating “Om” (or Aum)—a meditation symbol that represents the universe in its entirety. The concept of examining existence from a global perspective has begun to take hold in cancer research as well. Indeed, researchers have created their own “omes”: the genome, the transcriptome, the proteome. Here, Fang et al. examine the methylome of breast cancer and find a signature that may predict metastasis. The authors used genome-wide analysis to examine methylome signatures in breast cancers with various metastatic behaviors and found a signature that was associated with low metastatic risk and improved rates of survival. This breast CpG island methylator phenotype (B-CIMP) tracked with reduced metastasis independently of other breast cancer markers [such as estrogen receptor/progesterone receptor (ER/PR) and human epidermal growth factor receptor 2 (HER2) status] and was shared by multiple human malignancies, including glioma and colon cancer. However, altered methylation status may not just be a marker of metastasis: Methylation of B-CIMP signature genes correlated with transcriptional diversity among breast cancers with different prognoses. Thus, the B-CIMP phenotype may thus play a mechanistic role in metastatic risk, and future meditation on the methylome may improve breast cancer prognosis and therapy. Cancer-specific alterations in DNA methylation are hallmarks of human malignancies; however, the nature of the breast cancer epigenome and its effects on metastatic behavior remain obscure. To address this issue, we used genome-wide analysis to characterize the methylomes of breast cancers with diverse metastatic behavior. Groups of breast tumors were characterized by the presence or absence of coordinate hypermethylation at a large number of genes, demonstrating a breast CpG island methylator phenotype (B-CIMP). The B-CIMP provided a distinct epigenomic profile and was a strong determinant of metastatic potential. Specifically, the presence of the B-CIMP in tumors was associated with low metastatic risk and survival, and the absence of the B-CIMP was associated with high metastatic risk and death. B-CIMP loci were highly enriched for genes that make up the metastasis transcriptome. Methylation at B-CIMP genes accounted for much of the transcriptomal diversity between breast cancers of varying prognosis, indicating a fundamental epigenomic contribution to metastasis. Comparison of the loci affected by the B-CIMP with those affected by the hypermethylator phenotype in glioma and colon cancer revealed that the CIMP signature was shared by multiple human malignancies. Our data provide a unifying epigenomic framework linking breast cancers with varying outcome and transcriptomic changes underlying metastasis. These findings significantly enhance our understanding of breast cancer oncogenesis and aid the development of new prognostic biomarkers for this common malignancy.