Agnostic Administration of Targeted Anticancer Drugs: Looking for a Balance between Hype and Caution.

Many tumors have well-defined vulnerabilities, thus potentially allowing highly specific and effective treatment. There is a spectrum of actionable genetic alterations which are shared across various tumor types and, therefore, can be targeted by a given drug irrespective of tumor histology. Several agnostic drug-target matches have already been approved for clinical use, e.g., immune therapy for tumors with microsatellite instability (MSI) and/or high tumor mutation burden (TMB), NTRK1-3 and RET inhibitors for cancers carrying rearrangements in these kinases, and dabrafenib plus trametinib for BRAF V600E mutated malignancies. Multiple lines of evidence suggest that this histology-independent approach is also reasonable for tumors carrying ALK and ROS1 translocations, biallelic BRCA1/2 inactivation and/or homologous recombination deficiency (HRD), strong HER2 amplification/overexpression coupled with the absence of other MAPK pathway-activating mutations, etc. On the other hand, some well-known targets are not agnostic: for example, PD-L1 expression is predictive for the efficacy of PD-L1/PD1 inhibitors only in some but not all cancer types. Unfortunately, the individual probability of finding a druggable target in a given tumor is relatively low, even with the use of comprehensive next-generation sequencing (NGS) assays. Nevertheless, the rapidly growing utilization of NGS will significantly increase the number of patients with highly unusual or exceptionally rare tumor-target combinations. Clinical trials may provide only a framework for treatment attitudes, while the decisions for individual patients usually require case-by-case consideration of the probability of deriving benefit from agnostic versus standard therapy, drug availability, associated costs, and other circumstances. The existing format of data dissemination may not be optimal for agnostic cancer medicine, as conventional scientific journals are understandably biased towards the publication of positive findings and usually discourage the submission of case reports. Despite all the limitations and concerns, histology-independent drug-target matching is certainly feasible and, therefore, will be increasingly utilized in the future.

Ethnicity-specific BRCA1, BRCA2, PALB2, and ATM pathogenic alleles in breast and ovarian cancer patients from the North Caucasus.

BACKGROUND: Mountain areas of the North Caucasus host several large ethnic communities that have preserved their national identity over the centuries. METHODS: This study involved high-grade serous ovarian cancer (HGSOC) and breast cancer (BC) patients from Dagestan (HGSOC: 37; BC: 198), Kabardino-Balkaria (HGSOC: 68; BC: 155), North Ossetia (HGSOC: 51; BC: 104), Chechnya (HGSOC: 68; BC: 79), Ingushetia (HGSOC: 19; BC: 103), Karachay-Cherkessia (HGSOC: 13; BC: 47), and several Armenian settlements (HGSOC: 16; BC: 101). The group of BC patients was enriched by young-onset and/or family history-positive and/or bilateral and/or receptor triple-negative cases. The entire coding region of BRCA1, BRCA2, PALB2, and ATM genes was analyzed by next-generation sequencing. RESULTS: A significant contribution of BRCA1/2 pathogenic variants (PVs) to HGSOC and BC development was observed across all North Caucasus regions (HGSOC: 19-39%; BC: 6-13%). Founder alleles were identified in all ethnic groups studied, e.g., BRCA1 c.3629_3630delAG in Chechens, BRCA2 c.6341delC in North Ossetians, BRCA2 c.5351dupA in Ingush, and BRCA1 c.2907_2910delTAAA in Karachays. Some BRCA1/2 alleles, particularly BRCA2 c.9895C > T, were shared by several nationalities. ATM PVs were detected in 14 patients, with c.1673delG and c.8876_8879delACTG alleles occurring twice each. PALB2 heterozygosity was observed in 5 subjects, with one variant seen in 2 unrelated women. CONCLUSION: This study adds to the evidence for the global-wide contribution of BRCA1/2 genes to HGSOC and BC morbidity, although the spectrum of their PVs is a subject of ethnicity-specific variations. The data on founder BRCA1/2 alleles may be considered when adjusting the BRCA1/2 testing procedure to the ethnic origin of patients.

Rapid and Cost-Efficient Detection of RET Rearrangements in a Large Consecutive Series of Lung Carcinomas.

RET-kinase-activating gene rearrangements occur in approximately 1-2% of non-small-cell lung carcinomas (NSCLCs). Their reliable detection requires next-generation sequencing (NGS), while conventional methods, such as immunohistochemistry (IHC), fluorescence in situ hybridization (FISH) or variant-specific PCR, have significant limitations. We developed an assay that compares the level of RNA transcripts corresponding to 5'- and 3'-end portions of the RET gene; this test relies on the fact that RET translocations result in the upregulation of the kinase domain of the gene and, therefore, the 5'/3'-end expression imbalance. The present study included 16,106 consecutive NSCLC patients, 14,449 (89.7%) of whom passed cDNA quality control. The 5'/3'-end unbalanced RET expression was observed in 184 (1.3%) tumors, 169 of which had a sufficient amount of material for the identification of translocation variants. Variant-specific PCR revealed RET rearrangements in 155/169 (91.7%) tumors. RNA quality was sufficient for RNA-based NGS in 10 cases, 8 of which carried exceptionally rare or novel (HOOK1::RET and ZC3H7A::RET) RET translocations. We also applied variant-specific PCR for eight common RET rearrangements in 4680 tumors, which emerged negative upon the 5'/3'-end unbalanced expression test; 33 (0.7%) of these NSCLCs showed RET fusion. While the combination of the analysis of 5'/3'-end RET expression imbalance and variant-specific PCR allowed identification of RET translocations in approximately 2% of consecutive NSCLCs, this estimate approached 120/2361 (5.1%) in EGFR/KRAS/ALK/ROS1/BRAF/MET-negative carcinomas. RET-rearranged tumors obtained from females, but not males, had a decreased level of expression of thymidylate synthase (p < 0.00001), which is a known predictive marker of the efficacy of pemetrexed. The results of our study provide a viable alternative for RET testing in facilities that do not have access to NGS due to cost or technical limitations.

Hereditary cancer syndromes.

Hereditary cancer syndromes (HCSs) are arguably the most frequent category of Mendelian genetic diseases, as at least 2% of presumably healthy subjects carry highly-penetrant tumor-predisposing pathogenic variants (PVs). Hereditary breast-ovarian cancer and Lynch syndrome make the highest contribution to cancer morbidity; in addition, there are several dozen less frequent types of familial tumors. The development of the majority albeit not all hereditary malignancies involves two-hit mechanism, i.e. the somatic inactivation of the remaining copy of the affected gene. Earlier studies on cancer families suggested nearly fatal penetrance for the majority of HCS genes; however, population-based investigations and especially large-scale next-generation sequencing data sets demonstrate that the presence of some highly-penetrant PVs is often compatible with healthy status. Hereditary cancer research initially focused mainly on cancer detection and prevention. Recent studies identified multiple HCS-specific drug vulnerabilities, which translated into the development of highly efficient therapeutic options.

KRAS, NRAS, BRAF, HER2 and MSI Status in a Large Consecutive Series of Colorectal Carcinomas.

This study aimed to analyze clinical and regional factors influencing the distribution of actionable genetic alterations in a large consecutive series of colorectal carcinomas (CRCs). KRAS, NRAS and BRAF mutations, HER2 amplification and overexpression, and microsatellite instability (MSI) were tested in 8355 CRC samples. KRAS mutations were detected in 4137/8355 (49.5%) CRCs, with 3913 belonging to 10 common substitutions affecting codons 12/13/61/146, 174 being represented by 21 rare hot-spot variants, and 35 located outside the "hot" codons. KRAS Q61K substitution, which leads to the aberrant splicing of the gene, was accompanied by the second function-rescuing mutation in all 19 tumors analyzed. NRAS mutations were detected in 389/8355 (4.7%) CRCs (379 hot-spot and 10 non-hot-spot substitutions). BRAF mutations were identified in 556/8355 (6.7%) CRCs (codon 600: 510; codons 594-596: 38; codons 597-602: 8). The frequency of HER2 activation and MSI was 99/8008 (1.2%) and 432/8355 (5.2%), respectively. Some of the above events demonstrated differences in distribution according to patients' age and gender. In contrast to other genetic alterations, BRAF mutation frequencies were subject to geographic variation, with a relatively low incidence in areas with an apparently warmer climate (83/1726 (4.8%) in Southern Russia and North Caucasus vs. 473/6629 (7.1%) in other regions of Russia, p = 0.0007). The simultaneous presence of two drug targets, BRAF mutation and MSI, was observed in 117/8355 cases (1.4%). Combined alterations of two driver genes were detected in 28/8355 (0.3%) tumors (KRAS/NRAS: 8; KRAS/BRAF: 4; KRAS/HER2: 12; NRAS/HER2: 4). This study demonstrates that a substantial portion of RAS alterations is represented by atypical mutations, KRAS Q61K substitution is always accompanied by the second gene-rescuing mutation, BRAF mutation frequency is a subject to geographical variations, and a small fraction of CRCs has simultaneous alterations in more than one driver gene.

Strong founder effect for BRCA1 c.3629_3630delAG pathogenic variant in Chechen patients with breast or ovarian cancer.

Coding sequences of BRCA1, BRCA2, ATM, TP53, and PALB2 genes were analyzed in 68 consecutive Chechen patients with high-grade serous ovarian cancer (HGSOC). Pathogenic BRCA1/2 variants were identified in 15 (22%) out of 68 HGSOC cases. Nine out of ten patients with BRCA1 pathogenic alleles carried the same deletion (c.3629_3630delAG), and three out of five BRCA2 heterozygotes had Q3299X allele. The analysis of 49 consecutive patients with triple-negative breast cancer (TNBC) revealed 3 (6%) additional BRCA1 heterozygotes. All women with BRCA1 c.3629_3630delAG allele also carried linked c.1067G>A (Q356R) single nucleotide polymorphism, indicating that this is a genuine founder variant but not a mutational hotspot. An ATM truncating allele was detected in one HGSOC patient. There were no women with TP53 or PALB2 germline alterations. Genetic analysis of non-selected HGSOC patients is an efficient tool for the identification of ethnicity-specific BRCA1/2 pathogenic variants.

Preparation of Duplex Sequencing Libraries for Archival Paraffin-Embedded Tissue Samples Using Single-Strand-Specific Nuclease P1.

DNA from formalin-fixed paraffin-embedded (FFPE) tissues, which are frequently utilized in cancer research, is significantly affected by chemical degradation. It was suggested that approaches that are based on duplex sequencing can significantly improve the accuracy of mutation detection in FFPE-derived DNA. However, the original duplex sequencing method cannot be utilized for the analysis of formalin-fixed paraffin-embedded (FFPE) tissues, as FFPE DNA contains an excessive number of damaged bases, and these lesions are converted to false double-strand nucleotide substitutions during polymerase-driven DNA end repair process. To resolve this drawback, we replaced DNA polymerase by a single strand-specific nuclease P1. Nuclease P1 was shown to efficiently remove RNA from DNA preparations, to fragment the FFPE-derived DNA and to remove 5'/3'-overhangs. To assess the performance of duplex sequencing-based methods in FFPE-derived DNA, we constructed the Bottleneck Sequencing System (BotSeqS) libraries from five colorectal carcinomas (CRCs) using either DNA polymerase or nuclease P1. As expected, the number of identified mutations was approximately an order of magnitude higher in libraries prepared with DNA polymerase vs. nuclease P1 (626 ± 167/Mb vs. 75 ± 37/Mb, paired t-test p-value 0.003). Furthermore, the use of nuclease P1 but not polymerase-driven DNA end repair allowed a reliable discrimination between CRC tumors with and without hypermutator phenotypes. The utility of newly developed modification was validated in the collection of 17 CRCs and 5 adjacent normal tissues. Nuclease P1 can be recommended for the use in duplex sequencing library preparation from FFPE-derived DNA.

Somatic loss of the remaining allele occurs approximately in half of CHEK2-driven breast cancers and is accompanied by a border-line increase of chromosomal instability.

PURPOSE: Germline mutations in CHEK2 gene represent the second most frequent cause of hereditary breast cancer (BC) after BRCA1/2 lesions. This study aimed to identify the molecular characteristics of CHEK2-driven BCs. METHODS: Loss of heterozygosity (LOH) for the remaining CHEK2 allele was examined in 50 CHEK2-driven BCs using allele-specific PCR assays for the germline mutations and analysis of surrounding single-nucleotide polymorphisms (SNPs). Paired tumor and normal DNA samples from 25 cases were subjected to next-generation sequencing analysis. RESULTS: CHEK2 LOH was detected in 28/50 (56%) BCs. LOH involved the wild-type allele in 24 BCs, mutant CHEK2 copy was deleted in 3 carcinomas, while in one case the origin of the deleted allele could not be identified. Somatic PIK3CA and TP53 mutations were present in 13/25 (52%) and 4/25 (16%) tumors, respectively. Genomic features of homologous recombination deficiency (HRD), including the HRD score ≥ 42, the predominance of BRCA-related mutational signature 3, and the high proportion of long (≥ 5 bp) indels, were observed only in 1/20 (5%) BC analyzed for chromosomal instability. Tumors with the deleted wild-type CHEK2 allele differed from LOH-negative cases by elevated HRD scores (median 23 vs. 7, p = 0.010) and higher numbers of chromosomal segments affected by copy number aberrations (p = 0.008). CONCLUSION: Somatic loss of the wild-type CHEK2 allele is observed in approximately half of CHEK2-driven BCs. Tumors without CHEK2 LOH are chromosomally stable. BCs with LOH demonstrate some signs of chromosomal instability; however, its degree is significantly lower as compared to BRCA1/2-associated cancers.

Cancer Therapy Guided by Mutation Tests: Current Status and Perspectives.

The administration of many cancer drugs is tailored to genetic tests. Some genomic events, e.g., alterations of EGFR or BRAF oncogenes, result in the conformational change of the corresponding proteins and call for the use of mutation-specific compounds. Other genetic perturbations, e.g., HER2 amplifications, ALK translocations or MET exon 14 skipping mutations, cause overproduction of the entire protein or its kinase domain. There are multilocus assays that provide integrative characteristics of the tumor genome, such as the analysis of tumor mutation burden or deficiency of DNA repair. Treatment planning for non-small cell lung cancer requires testing for EGFR, ALK, ROS1, BRAF, MET, RET and KRAS gene alterations. Colorectal cancer patients need to undergo KRAS, NRAS, BRAF, HER2 and microsatellite instability analysis. The genomic examination of breast cancer includes testing for HER2 amplification and PIK3CA activation. Melanomas are currently subjected to BRAF and, in some instances, KIT genetic analysis. Predictive DNA assays have also been developed for thyroid cancers, cholangiocarcinomas and urinary bladder tumors. There is an increasing utilization of agnostic testing which involves the analysis of all potentially actionable genes across all tumor types. The invention of genomically tailored treatment has resulted in a spectacular improvement in disease outcomes for a significant portion of cancer patients.

Efficacy of lorlatinib in lung carcinomas carrying distinct ALK translocation variants: The results of a single-center study.

BACKGROUND: Lorlatinib is a novel potent ALK inhibitor, with only a few studies reporting the results of its clinical use. METHODS: This study describes the outcomes of lorlatinib treatment for 35 non-small cell lung cancer patients with ALK rearrangements, who had 2 (n = 5), 1 (n = 26) or none (n = 4) prior tyrosine kinase inhibitors and received lorlatinib mainly within the compassionate use program. RESULTS: Objective tumor response (OR) and disease control (DC) were registered in 15/35 (43%) and 33/35 (94%) patients, respectively; brain metastases were particularly responsive to the treatment (OR: 22/27 (81%); DC: 27/27 (100%)). Median progression free survival (PFS) was estimated to be 21.8 months, and median overall survival (OS) approached to 70.1 months. Only 4 out of 35 patients experienced no adverse effects; two of them were the only subjects who had no clinical benefit from lorlatinib. PFS and OS in the no-adverse-events lorlatinib users were strikingly lower as compared to the remaining patients (1.1 months vs. 23.7 months and 10.5 months vs. not reached, respectively; p < 0.0001 for both comparisons). ALK translocation variants were known for 28 patients; there was no statistical difference between patients with V.1 and V.3 rearrangements with regard to the OS or PFS. CONCLUSION: Use of lorlatinib results in excellent disease outcomes, however caution must be taken for patients experiencing no adverse effects from this drug.

Revisiting multiple erroneous genetic testing results and clinical misinterpretations in a patient with Li-Fraumeni syndrome: lessons for translational medicine.

BACKGROUND: Many cancer patients undergo sophisticated laboratory testing, which requires proper interpretation and interaction between different specialists. CASE PRESENTATION: We describe a patient with an extensive family history of cancer, who was diagnosed with bilateral breast cancer and two lung cancer lumps by the age of 40 years. She submitted a lung cancer specimen to a genetic profiling service, which reported the presence of the EGFR mutation (a combination of G719S and L833V substitutions) and the TP53 с.322_327del (p.G108_F109del) mutation in the tumor tissue. Possible therapeutic options were discussed at a medical conference, where one of the discussants raised a concern that the identified TP53 mutation may not necessarily be somatic, but reflect the germ-line status of the gene. Review of clinical records and follow-up dialog with the patient revealed, that she previously provided her blood for DNA analysis in two laboratories. The first laboratory utilized a custom NGS assay and did not detect the TP53 mutation, instead pointed to a potential pathogenic significance of the MSH6 c.2633 T > C (p.V878A) allele. The second laboratory revealed the TP53 с.322_327del (p.G108_F109del) allele but stated in the written report that it has an unknown pathogenic significance. To resolve the possible uncertainty regarding the role of the TP53 с.322_327del (p.G108_F109del) variant, we suggested that the patient invite her second cousin for genetic testing, as she was affected by neuroblastoma at the age of 3 years. This analysis revealed the presence of the same TP53 variant. CONCLUSION: We provide point-by-point discussion, reviewing multiple laboratory mistakes and clinical misinterpretations occurred with this patient. This case report exemplifies the need to involve rigorous clinical expertise in the daily practice of medical laboratory facilities.

Small fraction of testicular cancer cases may be causatively related to CHEK2 inactivating germ-line mutations: evidence for somatic loss of the remaining CHEK2 allele in the tumor tissue.

A recent study suggested a role of CHEK2 loss-of-function germ-line pathogenic variants in the predisposition to testicular cancer (TC) (AlDubayan et al. JAMA Oncol 5:514-522, 2019). We attempted to validate this finding relying on the high population frequency of recurrent CHEK2 pathogenic variants in Slavic populations. CHEK2 pathogenic alleles (c.1100delC (p.Thr367Metfs); del5395 [del ex9-10]; IVS2 + 1G > A [c.444 + 1G > A]) were detected in 7/280 (2.5%) TC patients vs. 3/424 (0.7%) healthy men and 6/1007 (0.6%) healthy women [OR 4.0 (95% CI 1.5-11), p = 0.009 for pooled control groups]. Somatic CHEK2 loss-of-heterozygosity (LOH) was detected in 4 out of 6 tumors available for analysis; strikingly all these instances of LOH involved inactivation of the wild-type allele. The CHEK2 c.470T > C (p.Ile157Thr) variant was detected in 21/280 (7.5%) affected vs. 22/424 (5.2%) non-affected men [OR 1.5 (95% CI 0.8-2.7), p = 0.3]. Somatic CHEK2 LOH was revealed only in 6 out of 21 tumors obtained from CHEK2 c.470T > C (p.Ile157Thr) carriers, with the C-allele lost in two cases and T-allele deleted in four tumors. The results of comparison of allele frequencies in TC patients versus population controls coupled with the data on CHEK2 LOH status in tumor tissues support the association of CHEK2 pathogenic variants with TC risk.

Frequency and spectrum of founder and non-founder BRCA1 and BRCA2 mutations in a large series of Russian breast cancer and ovarian cancer patients.

BACKGROUND: The spectrum of BRCA1 and BRCA2 mutations in Slavic countries is characterized by a high prevalence of founder alleles. METHODS: We analyzed a large data set of Russian breast cancer (BC) and ovarian cancer (OC) patients, who were subjected to founder mutation tests or full-length BRCA1 and BRCA2 analysis. RESULTS: The most commonly applied test, which included four founder mutations (BRCA1: 5382insC, 4153delA, 185delAG; BRCA2: 6174delT), identified BRCA1 or BRCA2 heterozygosity in 399/8533 (4.7%) consecutive BC patients, 230/2317 (9.9%) OC patients, and 30/118 (25.4%) women with a combination of BC and OC. The addition of another four recurrent BRCA1 mutations to the test (BRCA1 C61G, 2080delA, 3819del5, 3875del4) resulted in evident increase in the number of identified mutation carriers (BC: 16/993 (1.6%); OC: 34/1289 (2.6%); BC + OC: 2/39 (5.1%)). Full-length sequencing of the entire BRCA1 and BRCA2 coding region was applied to 785 women, very most of whom demonstrated clinical signs of BRCA-driven disease, but turned out negative for all described above founder alleles. This analysis revealed additional BRCA1 or BRCA2 mutation carriers in 54/282 (19.1%) BC, 50/472 (10.6%) OC, and 13/31 (42%) BC + OC patients. The analysis of frequencies of founder and "rare" BRCA1 and BRCA2 pathogenic alleles across various clinical subgroups (BC vs. OC vs. BC + OC; family history positive vs. negative; young vs. late-onset; none vs. single vs. multiple clinical indicators of BRCA1- or BRCA2-associated disease) revealed that comprehensive BRCA1 and BRCA2 analysis increased more than twice the number of identified mutation carriers in all categories of the examined women. CONCLUSION: Full-length BRCA1 and BRCA2 sequencing is strongly advised to Slavic subjects, who have medical indications for BRCA1 and BRCA2 testing but are negative for recurrent BRCA1 and BRCA2 mutations.

The spectrum of Lynch syndrome-associated germ-line mutations in Russia.

Hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome (LS), is a common cancer-predisposing syndrome. This study aimed to investigate the spectrum of germ-line mutations in Russian LS patients. LS-related mismatch repair (MMR) genes were analyzed in 16 patients, who were forwarded to genetic testing due to strong clinical features of LS and had high-level microsatellite instability (MSI-H) in the tumor (n = 14) or unknown MSI status (n = 2). In addition, 672 consecutive colorectal cancer (CRC) cases were screened for family history; 15 patients were younger than 50 years and reported 2 or more instances of LS-related cancers in 1st- or 2nd-degree relatives. Seven of these cases demonstrated MSI-H and therefore were subjected to DNA germ-line testing. Overall, 17/23 (74%) subjects carried LS-associated gene variants (MLH1: 10; MSH2: 4; MSH6: 2; PMS2: 1), with 2 alleles (MLH1 c.677G > T and MSH2 с.1906G > C) detected twice. Testing for recurrent mutations of 30 consecutive MSI-H CRCs led to the identification of 2 additional subjects with LS. The analysis of all relevant publications identified 28 unrelated LS patients presented in Russian medical literature and 3 unrelated Russian LS subjects described in international journals. Overall, 15/49 (31%) genetic defects revealed in Russian LS patients were represented by six recurrent alleles (MLH1: c.350C > T, c.677G > T, c.1852_1854del; MSH2: c.942+3A > T, c.1861C > T, с.1906G > C). We conclude that the founder effect for LS in Russia is seemingly less pronounced than the one for hereditary breast-ovarian cancer syndrome, however testing for recurrent LS mutations may be considered feasible in some circumstances.

Exome sequencing study of Russian breast cancer patients suggests a predisposing role for USP39.

PURPOSE: Germline variants in known breast cancer (BC) predisposing genes explain less than half of hereditary BC cases. This study aimed to identify missing genetic determinants of BC. METHODS: Whole exome sequencing (WES) of lymphocyte DNA was performed for 49 Russian patients with clinical signs of genetic BC predisposition, who lacked Slavic founder mutations in BRCA1, BRCA2, CHEK2, and NBS1 genes. RESULTS: Bioinformatic analysis of WES data was allowed to compile a list of 229 candidate mutations. 79 of these mutations were subjected to a three-stage case-control analysis. The initial two stages, which involved up to 797 high-risk BC patients, 1504 consecutive BC cases, and 1081 healthy women, indicated a potentially BC-predisposing role for 6 candidates, i.e., USP39 c.*208G > C, PZP p.Arg680Ter, LEPREL1 p.Pro636Ser, SLIT3 p.Arg154Cys, CREB3 p.Lys157Glu, and ING1 p.Pro319Leu. USP39 c.*208G > C was strongly associated with triple-negative breast tumors (p = 0.0001). In the third replication stage, we genotyped the truncating variant of PZP (rs145240281) and the potential splice variant of USP39 (rs112653307) in three independent cohorts of Russian, Byelorussian, and German ancestry, comprising a total of 3216 cases and 2525 controls. The data obtained for USP39 rs112653307 supported the association identified in the initial stages (the combined OR 1.72, p = 0.035). CONCLUSIONS: This study suggests the role of a rare splicing variant in BC susceptibility. USP39 encodes an ubiquitin-specific peptidase that regulates cancer-relevant tumor suppressors including CHEK2. Further epidemiological and functional studies involving these gene variants are warranted.

Mechanisms of acquired tumor drug resistance.

Systemic therapy often results in the reduction of tumor size but rarely succeeds in eradicating all cancer cells. Drug efflux, persistence of cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT) and down-regulation of apoptosis are the most known general causes of therapy failure. Tumor escape from targeted compounds often involves pathway-specific mechanisms, which result in the restoration of the affected signaling cascade. The acquisition of drug resistance is mediated by mutations, changes in gene expression, alternative splicing, post-translational protein modifications, etc. Development of resistance to therapy may not necessary involve the emergence of new tumor clones: multiple studies demonstrate that even chemonaive neoplasms already have a small population of cells, which are capable of surviving therapeutic pressure and facilitating the disease progression. Use of combinations of cancer drugs, sequential therapy, adaptive therapy and topical ablation of drug-resistant malignant lumps may help to prolong the time to treatment failure. Many studies on mechanisms of drug resistance rely on the use of cell cultures and animal models. The development of approaches that allow efficient monitoring of the evolution of tumor phenotype in clinical setting presents a challenge.

Lack of Response to Vemurafenib in Melanoma Carrying BRAF K601E Mutation.

Vemurafenib has been developed to target common BRAF mutation V600E. It also exerts activity towards some but not all rare BRAF substitutions. Proper cataloguing of drug-sensitive and -insensitive rare mutations remains a challenge, due to low occurrence of these events and inability of commercial PCR-based diagnostic kits to detect the full spectrum of BRAF gene lesions. We considered the results of BRAF exon 15 testing in 1872 consecutive melanoma patients. BRAF mutation was identified in 1,090 (58.2%) cases. While drug-sensitive codon 600 substitutions constituted the majority of BRAF gene lesions (V600E: 962 [51.4%]; V600K: 86 [4.6%]; V600R: 17 [0.9%]), the fourth common BRAF allele was K601E accounting for 9 (0.5%) melanoma cases. The data on BRAF inhibitor sensitivity of tumors with K601E substitution are scarce. We administered single-agent vemurafenib to a melanoma patient carrying BRAF K601E mutation as the first-line treatment. Unfortunately, this therapy did not result in a tumor response. Taken together with already published data, this report indicates lack of benefit from conventional BRAF inhibitors in patients with BRAF K601E mutated melanoma.

Lack of Response to Imatinib in Melanoma Carrying Rare KIT Mutation p.T632I.

Approximately 15% of acral and mucous melanomas carry activating mutations in KIT oncogene. There is a diversity of spectrum of KIT mutations, with some of them rendering tumors responsive to imatinib, while others being imatinib-resistant or not studied yet. Here we present an acral melanoma patient with KIT р.T632I mutation, who failed to respond to imatinib.

Exome-based search for recurrent disease-causing alleles in Russian population.

Exomes of 27 Russian subjects were analyzed for the presence of medically relevant alleles, such as protein-truncating variants (PTVs) in known recessive disease-associated genes and pathogenic missense mutations included in the ClinVar database. 36 variants (24 PTVs and 12 amino acid substitutions) were identified and then subjected to the analysis in 897 population controls. 9/36 mutations were novel, however only two of them (POLH c.490delG associated with xeroderma pigmentosum variant (XPV) and CATSPER1 c.859_860delCA responsible for spermatogenic failure) were shown to be recurrent. 27 out of 36 pathogenic alleles were already described in prior genetic studies; seven of them occurred only in the index cases, while 20 demonstrated evidence for persistence in Russian population. In particular, non-random occurrence was revealed for SERPINA1 c.1096G > A (alpha-1 antitrypsin deficiency), C8B c.1282C > T and c.1653G > A (complement component 8B deficiency), ATP7B c.3207C > A (Wilson disease), PROP1 c.301_302delAG (combined pituitary hormone deficiency), CYP21A2 c.844G > T (non-classical form of adrenogenital syndrome), EYS c.1155T > A (retinitis pigmentosa), HADHA c.1528G > C (LCHAD deficiency), SCO2 c.418G > A (cytochrome c oxidase deficiency), OTOA c.2359G > T (sensorineural deafness), C2 c.839_866del (complement component 2 deficiency), ACADVL c.848T > C (VLCAD deficiency), TGM5 c.337G > T (acral peeling skin syndrome) and VWF c.2561 G > A (von Willebrand disease, type 2N). These data deserve to be considered in future medical genetic activities.

First-Line Cetuximab Monotherapy in KRAS/NRAS/BRAF Mutation-Negative Colorectal Cancer Patients.

BACKGROUND: Colorectal carcinomas (CRCs) are sensitive to treatment by anti-epidermal growth factor receptor (EGFR) antibodies only if they do not carry activating mutations in down-stream EGFR targets (KRAS/NRAS/BRAF). Most clinical trials for chemo-naive CRC patients involved combination of targeted agents and chemotherapy, while single-agent cetuximab or panitumumab studies included either heavily pretreated patients or subjects who were not selected on the basis of molecular tests. We hypothesized that anti-EGFR therapy would have significant efficacy in chemo-naive patients with KRAS/NRAS/BRAF mutation-negative CRC. METHODS: Nineteen patients were prospectively included in the study. RESULTS: Two (11%) patients experienced partial response (PR) and 11 (58%) subjects showed stable disease (SD). Median time to progression approached 6.1 months (range 1.6-15.0 months). Cetuximab efficacy did not correlate with RNA expression of EGFR and insulin-like growth factor 2 (IGF2). Only one tumor carried PIK3CA mutation, and this CRC responded to cetuximab. Exome analysis of patients with progressive disease (PD) revealed 1 CRC with high-level microsatellite instability and 1 instance of HER2 oncogene amplification; 3 of 4 remaining patients with PD had allergic reactions to cetuximab, while none of the subjects with PR or SD had this complication. Comparison with 19 retrospective KRAS/NRAS/BRAF mutation-negative patients receiving first-line fluoropyrimidines revealed no advantages or disadvantages of cetuximab therapy. CONCLUSIONS: Cetuximab demonstrates only modest efficacy when given as a first-line monotherapy to KRAS/NRAS/BRAF mutation-negative CRC patients. It is of question, why meticulous patient selection, which was undertaken in the current study, did not result in the improvement of outcomes of single-agent cetuximab treatment.