PLX4032, a small-molecule inhibitor being developed by Plexxikon of California and Roche Pharmaceuticals in New Jersey ( http://go.nature.com/QnVGQx ), selectively targets B-RAFV600E, a mutant form of the B-RAF protein kinase common in several human cancers. In this issue of Nature, Gideon Bollag and colleagues report promising results for PLX4032 in an early clinical trial in melanoma patients who carry this B-RAF mutation. They also describe the structure and function of PLX4032 and present translational data from a phase I trial to show that clinical efficacy requires a drug concentration that is sufficient to cause a substantial degree of inhibition of the ERK pathway downstream of B-RAF. The study demonstrates how the design of early clinical trials based on the biological mechanisms underlying tumour formation has the potential to speed up the process by which anticancer drugs can reach the clinic. PLX4032 is a selective inhibitor of the B-RAF protein that has shown promising results in an early clinical trial in melanoma patients with an activating mutation in B-RAF. Now the structure and function of this inhibitor are described. Translational data from a phase I trial show that clinical efficacy requires a substantial degree of inhibition of the ERK pathway downstream of B-RAF. The data also show that BRAF-mutant melanomas are highly dependent on B-RAF activity. B-RAF is the most frequently mutated protein kinase in human cancers1. The finding that oncogenic mutations in BRAF are common in melanoma2, followed by the demonstration that these tumours are dependent on the RAF/MEK/ERK pathway3, offered hope that inhibition of B-RAF kinase activity could benefit melanoma patients. Herein, we describe the structure-guided discovery of PLX4032 (RG7204), a potent inhibitor of oncogenic B-RAF kinase activity. Preclinical experiments demonstrated that PLX4032 selectively blocked the RAF/MEK/ERK pathway in BRAF mutant cells and caused regression of BRAF mutant xenografts4. Toxicology studies confirmed a wide safety margin consistent with the high degree of selectivity, enabling Phase 1 clinical trials using a crystalline formulation of PLX4032 (ref. 5). In a subset of melanoma patients, pathway inhibition was monitored in paired biopsy specimens collected before treatment initiation and following two weeks of treatment. This analysis revealed substantial inhibition of ERK phosphorylation, yet clinical evaluation did not show tumour regressions. At higher drug exposures afforded by a new amorphous drug formulation4,5, greater than 80% inhibition of ERK phosphorylation in the tumours of patients correlated with clinical response. Indeed, the Phase 1 clinical data revealed a remarkably high 81% response rate in metastatic melanoma patients treated at an oral dose of 960 mg twice daily5. These data demonstrate that BRAF-mutant melanomas are highly dependent on B-RAF kinase activity.

The tuberous sclerosis complex (TSC), a multisystem, autosomal dominant disorder affecting children and adults, results from mutations in one of two genes, TSC1 (encoding hamartin) or TSC2 (encoding tuberin). In this article, the current knowledge of the pathogenesis of the disease and its management are discussed.

Background: Previously, small studies have found that BRCA1 and BRCA2 breast tumors differ in their pathology. Analysis of larger datasets of mutation carriers should allow further tumor characterization. Methods: We used data from 4,325 BRCA1 and 2,568 BRCA2 mutation carriers to analyze the pathology of invasive breast, ovarian, and contralateral breast cancers. Results: There was strong evidence that the proportion of estrogen receptor (ER)-negative breast tumors decreased with age at diagnosis among BRCA1 (P-trend = 1.2 × 10⁻⁵), but increased with age at diagnosis among BRCA2, carriers (P-trend = 6.8 × 10⁻⁶). The proportion of triple-negative tumors decreased with age at diagnosis in BRCA1 carriers but increased with age at diagnosis of BRCA2 carriers. In both BRCA1 and BRCA2 carriers, ER-negative tumors were of higher histologic grade than ER-positive tumors (grade 3 vs. grade 1; P = 1.2 × 10⁻¹³ for BRCA1 and P = 0.001 for BRCA2). ER and progesterone receptor (PR) expression were independently associated with mutation carrier status [ER-positive odds ratio (OR) for BRCA2 = 9.4, 95% CI: 7.0–12.6 and PR-positive OR = 1.7, 95% CI: 1.3–2.3, under joint analysis]. Lobular tumors were more likely to be BRCA2-related (OR for BRCA2 = 3.3, 95% CI: 2.4–4.4; P = 4.4 × 10⁻¹⁴), and medullary tumors BRCA1-related (OR for BRCA2 = 0.25, 95% CI: 0.18–0.35; P = 2.3 × 10⁻¹⁵). ER-status of the first breast cancer was predictive of ER-status of asynchronous contralateral breast cancer (P = 0.0004 for BRCA1; P = 0.002 for BRCA2). There were no significant differences in ovarian cancer morphology between BRCA1 and BRCA2 carriers (serous: 67%; mucinous: 1%; endometrioid: 12%; clear-cell: 2%). Conclusions/Impact: Pathologic characteristics of BRCA1 and BRCA2 tumors may be useful for improving risk-prediction algorithms and informing clinical strategies for screening and prophylaxis. Cancer Epidemiol Biomarkers Prev; 21(1); 134–47. ©2011 AACR.

Background: Increasing numbers of BRCA1 mutation carriers are being identified in cancer risk evaluation programs. However, no estimates of cancer risk specific to a clinic-based population of mutation carriers are available. These data are clinically relevant, because estimates based on families ascertained for linkage studies may overestimate cancer risk in mutation carriers, and population-based series may underestimate it. Wide variation in risk estimates from these disparate ascertainment groups makes counseling in risk evaluation programs difficult. The purpose of this study was to estimate BRCA1-related cancer risks for individuals ascertained in a breast cancer risk evaluation clinic. Methods: Cumulative observed and age-adjusted cancer risk estimates were determined by analyzing 483 BRCA1 mutation carriers in 147 families identified in two academic breast and ovarian cancer risk evaluation clinics. Cancer risks were computed from the proportion of individuals diagnosed with cancer during a 10-year age interval from among the total number of individuals alive and cancer-free at the beginning of that interval. Age-of-diagnosis comparisons were made using two-sided Student's t tests. Results: By age 70, female breast cancer risk was 72.8% (95% confidence interval [CI] = 67.9% to 77.7%) and ovarian cancer risk was 40.7% (95% CI = 35.7% to 45.6%). The risk for a second primary breast cancer by age 70 was 40.5% (95% CI = 34.1% to 47.0%). We also identified an increased risk of cancer of the colon (twofold), pancreas (threefold), stomach (fourfold), and fallopian tube (120-fold) in BRCA1 mutation carriers as compared with Surveillance, Epidemiology, and End Results (SEER) Program population-based estimates. Conclusion: The estimates for breast and ovarian cancer risk in BRCA1 mutation carriers is higher than population-based estimates but lower than estimates based on families ascertained for linkage studies. These cancer risk estimates may most closely approximate those faced by BRCA1 mutation carriers identified in risk evaluation clinics.