Frequency Of KIT Mutations Research Articles

Clinicopathological, immunohistochemical, molecular-genetic and risk profiles of gastrointestinal stromal tumors in a cohort of Sudanese patients.

Determining the risk of malignant behaviour and mutational status of gastrointestinal stromal tumours (GISTs) guide the management decision and allow optimal individualized patient treatment. To determine clinicopathological, immunohistochemical (IHC), risk and KIT mutational findings of GISTs in Sudanese patients. Histological slides were reviewed, IHC for DOG-1 and CD117 performed and hotspot KIT mutations examined. The risk group was assigned using combined risk criteria. 21 of the 36 patients (58.3%) were males (mean age, 54.83 ±12.57; range, 26-71). Abdominal pain and mass were the most frequent symptoms. Mean tumor size (±SD) was 11.6(±5.82) cm. Either CD117, DOG1 or both were positive in all cases. Using risk criteria, 33.3% (n=12) were clinically malignant at presentation, 13.9% (n=5) high risk, 16.7% (n=6) intermediate, 27.8% (n=10) low risk and 2.8% (n=1) very low risk. Sixteen of 23 (70%) tested cases had KIT (14 exon 11 and two exon 9) mutations. Six tumors were wild type. Exon 11 deletions (p.I563-L576 del and p.V559-N566delinsD) significantly correlate with disease recurrence (p-value: 0.028). Sudanese patients with GIST tend to present late. Nearly half of them correspond to the malignant/high-risk category. The frequency of KIT mutations (79.31%) is in line with the literature.

KIT Mutation Incidence and Pattern of Melanoma in Central Europe

Data on the KIT mutation rate in melanoma in the central European region is missing. Accordingly, in a cohort of 79 BRAF/NRAS double wild type cutaneous melanoma and 17 mucosal melanoma KIT mutation was assessed by Sanger sequencing of exons 9,11,13,17 and 18. In this cutaneous melanoma cohort KIT mutation frequency was found to be 34/79 (43.04%) with a significantly higher rate in acrolentiginous melanoma (ALM) as compared to UV-induced common variants (20/34, 58.8% versus 14/45, 31.1%, p = 0.014). In the double wild type mucosal melanoma cohort the KIT mutation frequency was found to be comparable (41.2%). The actual frequency of KIT mutation in the original 227 patient cutaneous melanoma cohort was 34/227, 14.9%. Exon 11 was the most frequent mutation site (44.7%) followed by exon 9 (21.1%) equally characterizing UV-induced common histotypes and ALM tumors. In mucosal melanoma exon 9 was the most frequently involved exon followed by exon 13 and 17. KIT mutation hotspots were identified in exon 9 (c482/491/492), in exon 11 (c559,c572, c570), in exon 13 (c642), in exon 17 (c822) and in exon 18 (c853). The relatively high KIT mutation rate in cutaneous melanoma in this central-European cohort justifies regular testing of this molecular target in this entity, not only in mucosal variants.

Acute myeloid leukemia with t(8;21)(q22;q22.1)/RUNX1-RUNX1T1 and KIT Exon 8 mutation is associated with characteristic mastocytosis and dismal outcomes

KIT mutations are observed in about 20–40% of acute myeloid leukemia with t(8;21)(q22;q22.1)/RUNX1-RUNX1T1 [abbreviated AML t(8;21) here] with mutations involving exon 17 being the most common. Despite high frequencies of KIT mutations in both AML t(8;21) and systemic mastocytosis (SM), AML t(8;21) associated with SM is uncommon, and restricted to KIT exon 17 mutated cases. In this study, we report two cases of AML t(8;21) associated SM that KIT mutation occurred in exon 8 (T417_D419delinsY). In both patients, the bone marrow displayed increased round/ovoid mast cells with bilobated nuclei and absence of CD2 and CD25 expression. RUNX1/RUNX1T1 fusion was shown in both myeloblasts and mast cells by FISH. Patient #1 was refractory to induction chemotherapy and died at day 50; patient #2 had residual AML, marked SM, and persistent RUNX1/RUNX1T1 fusion after induction therapy.

The clinical significance of KIT mutations in melanoma: a meta-analysis.

This study aimed to evaluate the association of KIT mutations with clinicopathologic features of melanomas using a meta-analysis and to identify differences between Asian and White populations using subgroup analyses. We selected 32 studies from the literature including 5224 patients. The pooled data were combined, and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Heterogeneity and publication bias were also determined. KIT mutations were reported in 497 (9.5%) of 5224 patients with melanomas, and were associated significantly with age, clinical melanoma subtype, anatomic location, and chronic sun-damage (CSD), but not with sex, histological type, Breslow thickness, ulceration, mitotic rate, or tumor stage. The incidence of KIT mutation was significantly higher in older individuals (OR=1.296, 95% CI: 1.025-1.641; P=0.031), and showed a positive association with mucosal melanoma (OR=1.363, 95% CI: 1.094-1.697; P=0.006), acral melanoma (OR=1.374, 95% CI: 1.123-1.682; P=0.02), and CSD (OR=1.880, 95% CI: 1.127-3.136; P=0.016), but a negative relationship with melanomas arising in non-CSD skin (OR=0.562, 95% CI: 0.392-0.805; P=0.002). The frequency of KIT mutations was associated negatively with melanomas located on the extremities. KIT mutations, which are critical in the genetic pathogenesis of melanomas, define a unique subtype of melanoma associated closely with older age, and acral, mucosal, or CSD sites, but not associated with any histological features or tumor stage. Although the KIT mutation rate is higher in White than Asian populations, no significant difference in clinical association with KIT mutations was detected between the two groups.

Abstract 4341: Large mutational spectrum of cutaneous melanoma in a Brazilian population: The experience of A.C. Camargo Cancer Center

Abstract Introduction: Cutaneous melanoma (CM) is an aggressive type of malignancy, with elevated mortality rates. The Cancer Genome Atlas Network (TCGA) recently reported the molecular classification of CM and divided these lesions according to their somatic mutation profile in 4 categories: BRAF, NRAS or NF1 mutated, and also the triple-negative group. The aim of this study is to describe the spectrum of molecular alterations from a Brazilian population of CM patients. Methods: DNA was extracted from formalin-fixed, paraffin-embedded (FFPE) tissue from primary and metastatic melanoma samples from A.C. Camargo Cancer Center molecular pathology section. Next-generation sequencing (Ion Torrent®) targeting a 14-gene panel was performed, targeting the following genes: BRAF (códon 600), NRAS (códons 12, 13, 61, 117 and 146) e KIT (éxon 11, 13, 17), KRAS, CTNNB1, IDH1, EGFR, HRAS, PDGFR-a, PIK3CA, RET, JAK2, MET, and CDH1. Results: 131 cutaneous melanoma samples from different patients were sequenced. The majority of the samples (57%) showed mutation in at least one gene. BRAF was the most frequent detected mutation, found in 40% of the cases, and p.V600E, p.V600K and p.V600R represented 90%, 8% and 2% of BRAF mutations, respectively. NRAS mutation was detected in 10% of the cases, and among those 88% involved codon 61. KIT mutation was identified in 10% of the cases. Mutations in KRAS, CTNNB1, PDGFRa, PIK3CA, EGFR and HRAS were identified in 5%, 4%, 4%, 3%, 2% and 1% of the cases, respectively. No mutations in IDH1, JAK2, MET or RET was identified. Most of the mutated cases showed mutation in only one tested gene (71%), while 14%, 10% and 5% showed mutations in 2, 3 or 4 genes respectively. None of the cases showed simultaneous mutation involving combinations of BRAF, NRAS or KIT mutations. Discussion and Conclusion: The BRAF, NRAS and KIT mutation frequency in this population with CM diagnosis is similar to the one described in the world literature for this disease, as well as the distribution of the most frequent mutated regions and specific types of mutations. These results add the mutational spectrum of CM of a large Brazilian cohort to the world literature. Treatment of CM with targeted therapies aiming the MAP-Kinase pathway, and especially blocking BRAF, are a reality in the clinical oncology routine for treating CM patients, but there are still many obstacles in order to fully understand the resistance mechanism and the possibility of drug combinations. Additionally, new targeted agents are under development, such as the ones for NRAS mutated cases, and in this way the understanding of the large mutational spectrum of melanoma is of extreme importance in the clinical scenario. Citation Format: Mariana Petaccia de Macedo, Felipe Fidaldo, Clovis Lopes Pinto, João Pedreira Duprat, Maria Dirlei S.f Begnami, Dirce Maria Carraro, Isabela Werneck Cunha. Large mutational spectrum of cutaneous melanoma in a Brazilian population: The experience of A.C. Camargo Cancer Center [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4341.

Detection of KIT mutations in core binding factor acute myeloid leukemia

We have investigated the frequency and the effect of KIT mutations on the outcome of patients with CBF-AML. 69 patients (34 pediatrics and 35 adults) with CBF-AML were enrolled in the study. The frequency of KIT mutations was higher in adults compared to pediatrics (22.9% and 14.7%, p = 0.38) respectively. Leukocytosis ≥ 20 × 109 /L was significantly associated with pediatrics compared to adults. t(8;21)(q22;22) was significantly associated with thrombocytopenia in adults. We conclude that no significant difference is found between KIT mutated and unmutated CBF-AML in adults and pediatrics. Children with CBF-AML present with leukocytosis. t(8;21) is associated with thrombocytopenia.

Abstract LB-039: Translational research in a phase I proof-of-concept study supports that DCC-2618 is a pan-KIT inhibitor

Abstract Background: DCC-2618 is a potent switch control inhibitor of KIT and PDGFRα kinases maintains potent inhibition of mutant forms across all exon regions in preclinical models. Gastrointestinal stromal tumor (GIST) is an important disease to achieve a proof-of-concept due to the heterogeneity of resistance mutations in KIT which emerge on treatment with approved KIT inhibitors. In later lines of therapy resistance mechanisms independent of the KIT gene have also been described. Methods: The ongoing phase 1, PK-guided dose escalation study of DCC-2618 given orally BID [28-day cycle] tested doses from 20 mg to 200 mg in patients (pts) with advanced solid tumors including GIST (NCT02571036). We report preliminary longitudinal results of plasma cell free (cf) DNA sequencing by Guardant 360 collected throughout the study and levels of circulating tumor cells (CTCs) based on a viral telomerase promoter-driven GFP expression assay. Results: To date, 24 out of 31 enrolled pts had metastatic KITm GIST refractory to standard therapy. A high, total mean exposure of DCC-2618 and its active metabolite was achieved at 100 and 150 mg BID, affording steady state Cmax >5 µM in Cycle 1. Starting with 50 mg BID dose level, concentrations of total drug exceeding IC90 of the most resistant mutations to DCC-2618 were achieved. Next-generation sequencing of plasma cfDNA revealed a total of 40 KIT mutations in 16 of 18 GIST pts at baseline. DCC-2618 led to rapid decrease and/or clearance of the heterogeneous array of KIT mutations from plasma cfDNA including exons 9, 11, 13, 14, 17, and 18. Independent of suppressed KIT mutation burden, longitudinal monitoring of cfDNA revealed changes in non-KIT oncogenic mutations which may contribute to heterogenous mechanisms of resistance. KIT mutation burden will be correlated with metabolic response assessment by PET scans and exposure to DCC-2618. CTCs have been detected in blood from all GIST patients at baseline using a non-biased assay capable of identifying sarcoma cells. Preliminary result show that CTCs with immunofluorescent detection of KIT or PDGFRα, corresponding to their respective mutational status, show 1 of 3 patterns when compared to radiologic response: most pts show relatively stable low levels at stable disease (SD), a minority of pts with prolonged SD a decline in CTCs and 2 pts with progressive disease had significant increase in KIT positive CTCs. Conclusions: DCC-2618 and its active metabolite achieved high plasma concentrations sufficient to inhibit the most resistant KIT mutations at well-tolerated exposures. Monitoring of cfDNA KIT mutation frequency demonstrates rapid clearance of a broad spectrum of KIT mutations in this heavily pretreated GIST patient population and suggests candidate resistance genes that are independent of KIT. Our data provide a first signal that CTC monitoring might represent a potential marker for tumor control in KIT mutant GIST. Citation Format: Filip Janku, Albi Razak, Michael Gordon, David Brooks, Daniel Flynn, Anu Gupta, Michael Kaufman, Cynthia Leary, Bryan Smith, Deb Westwood, Neeta Somaiah, Elena Helman, Eric Gerstenberger, Oliver Rosen, Suzanne George. Translational research in a phase I proof-of-concept study supports that DCC-2618 is a pan-KIT inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-039. doi:10.1158/1538-7445.AM2017-LB-039

PDGFRA and KIT Mutation Status and Its Association With Clinicopathological Properties, Including DOG1.

Most of the gastrointestinal stromal tumors (GISTs) have gain-of-function mutations in the KIT gene, which can be used as a prognostic marker for the biological behavior of tumors, predictive marker for the response of tyrosine kinase inhibitors, and diagnostic marker. Researchers have focused on PDGFRA mutations because of both their prognostic and predictive potential and DOG1 positivity for diagnosis on GISTs. The aim of this study is to investigate the effect DOG1, PDGFRA, and KIT mutations on the prediction of the outcome for GIST management. Polymerase chain reaction was performed for KIT gene exons 9, 11, 13, and 17 and PDGFRA gene exons 12 and 18 with the genomic DNA of 46 GIST patients, and amplicons were sequenced in both directions. Immunocytochemical stainings were done by using primary antibodies. Molecular analysis revealed that the KIT mutation was observed in 63% of all cases, while the PDGFRA mutation was observed in 23.9% of cases. Significant relationships were found between age and KIT mutation, tumor location and KIT mutations, and tumor location and PDGFRA mutations (p ≤ 0.05). DOG1 positivity was detected in 65.2% of all GISTs and DOG1-positive cells had a higher KIT mutation ratio than DOG1-negative cells (p ≤ 0.05). KIT gene exon 11 mutations in DOG1-positive cells was higher than DOG1-negative cells (p ≤ 0.05). Conversely, KIT gene exon 13 mutations were higher in DOG1-negative cells than DOG1-positive cells (p ≤ 0.05). In this study, KIT mutation frequency was found similar with the European population; conversely, PDGFRA mutation frequency was similar with an Asian-Chinese-based study. KIT/PDGFRA mutations and tumor location can be used for the prediction of tumor behavior and the management of disease in GISTs. DOG1 positivity might be a candidate marker to support KIT and PDGFRA mutations, due to the higher DOG1 positivity in KIT exon 11 mutant and stomach- and small intestine-localized GISTs.

Analysis of KIT mutations and c-KIT expression in Chinese Uyghur and Han patients with melanoma.

The KIT gene plays an important role in the pathogenesis of malignant melanoma (MM). In recent years, activating mutations in KIT have been recognized as oncogenic. A number of therapies have been established, which provide significant clinical benefits for patients with MM with KIT mutations. Thus, detection of KIT mutations can have profound therapeutic implications. To investigate KIT gene expression in MMs in Chinese Uyghur and Han patients with mutations in KIT, and to identify the clinical features associated with KIT mutations and c-KIT expression. In total, 105 MMs (56 from Uyghur and 49 from Han patients) were selected from patients in the Uyghur Autonomous region. Formalin-fixed, paraffin wax-embedded tumour sections were analysed for c-KIT expression using immunohistochemistry. Exons 11 and 13 of KIT were analysed for the presence of mutations using PCR amplification and DNA sequencing. Of the 105 MMs, 13 (10 Han and 3 Uyghur) were found to have mutations in KIT. Thus, the frequency of KIT mutations in Han patients was significantly higher than that in Uyghur patients (P=0.02). We detected c-KIT expression in 71.4% and 42.9% of the tumour tissue samples collected from the Uyghur and Han patients, respectively. In the Xinjiang Uyghur Autonomous Region in China, chronic sun-induced damage MM is the most prevalent MM among Chinese Uyghur patients, whereas acral and mucosal MMs are the most prevalent in Uyghur patients. Mutations in the KIT gene do not correlate with c-KIT expression.

NRAS mutations are more prevalent than KIT mutations in melanoma of the female urogenital tract—A study of 24 cases from the Netherlands

ObjectiveThe aim of this study was to evaluate a series of primary melanomas of the female urogenital tract for oncogenic mutations in KIT, NRAS and BRAF in order to identify patients who may be amenable to targeted therapy. MethodsWe reviewed twenty-four cases of female urogenital tract melanomas and used Sanger sequencing analysis for the detection of oncogenic mutations in exons 9, 11, 13, and 17 of KIT; exons 2 and 3 of NRAS; and exon 15 of BRAF. ResultsTwenty-four patients were included: fourteen vaginal melanomas, four cervical melanomas, five urethral melanomas and one vulvar melanoma. NRAS mutations (4/24, 21%) were more prevalent than KIT mutations (1/24, 4%), while BRAF mutations were absent. Three of four NRAS mutations were present in vaginal melanomas (21%), mainly affecting codon 61 (3/4). They were mutually exclusive with the KIT mutation. The KIT mutation was present in a vaginal melanoma and affected exon 17. ConclusionsMelanomas of the female urogenital tract relatively commonly harbor mutations in NRAS; this makes NRAS an interesting therapeutic target for these patients in the advanced setting. KIT mutations were rare in our study in contrast to some previous reports. We cannot exclude that anatomical site-related differences and/or population related differences in KIT mutation frequency exist within urogenital tract melanomas.

Identification ofKITactivating mutations in paediatric solitary mastocytoma

Mastocytosis is an abnormal mast cell proliferation involving one or more organs, in particular the skin and bone marrow. In children, disease is usually limited to the skin, with three distinct clinical presentations: urticaria pigmentosa, diffuse cutaneous mastocytosis and solitary mastocytoma. Although the KIT D816V mutation is typically found in adult-onset mastocytosis, it is less commonly seen in childhood-onset mastocytosis, and the frequency of KIT mutations in paediatric solitary mastocytoma is poorly documented. In this study we analysed KIT exons 8, 9, 11, 13 and 17 in nine cases of paediatric solitary mastocytoma using a laboratory-developed Sanger sequencing assay. A KIT mutation was identified in six cases (67%), including three with the D816V mutation typical of adult-onset disease, and another three with an internal tandem duplication (p.A502_Y503dup) in exon 9, previously described in gastrointestinal stromal tumour. Paediatric solitary mastocytoma is frequently associated with KIT activating mutations, in keeping with a clonal process. KIT mutational status appears insufficient to explain the divergent biology of childhood and adult-onset disease.

Analysis of KIT expression and mutations in sinonasal, genital, and acrolentiginous melanomas.

8563 Background: Melanoma is subdivided into molecular defined groups. One major subtype is characterized by a mutation in the BRAF gene. BRAF is less commonly mutated in acrolentiginous (ALM) and mucosal (MM) melanomas, instead these subtypes predominantly show aberrations in the KIT/CD117 gene. KIT aberrations predict the outcome of targeted therapies in ALM and MM patients, however the particular role of KIT expression in these melanoma subtypes remains controversial. To explore the relationship between KIT expression, mutation, and tumor stages, we investigated immunohistochemical KIT expression and mutation status in primary ALM/MM lesions and their metastases. We also compared the frequency of KIT mutations of MM in different anatomic locations. Methods: KIT immunoreactivity and mutation status was assessed in 41 ALM and 25 MM patients, using polyclonal rabbit anti-human KIT/CD117 antibody, and PCR was performed for KIT gene exons 9,11,13,17 and 18. Of these, 19 ALM and 15 MM patients had matched primary and metastatic lesions. Phosphorylated extracellular regulated kinase (P-ERK) was investigated in a subset of 8 ALM and 8 MM matched primary/metastatic pairs by immunohistochemistry. Results: Heterogeneous KIT immunoreactivity was observed in both primary and metastatic lesions. Mutations were present in four of 41 ALM (10%) and five of 25 MM (20%) patients. Only vulvar mucosal samples carried KIT mutations in contrast to sinonasal lesions (p= 0.0109). In KIT-mutated tumors, the mutations were present in KIT expressing as well as KIT negative cells, as shown by Laser Capture Microdissection (LCM). P-ERK expression was preferentially found in metastases. Conclusions: KIT expression is heterogeneous and shows no relationship with disease progression and mutation status, therefore KIT immunoreactivity is not a valuable marker for treatment decisions. In mucosal melanoma patients, KIT mutation frequency is significantly associated with anatomic location. Vulvar melanoma patients are prone to carry activating KIT mutations and thus may be more likely to benefit from KIT-targeted therapies than other subtypes. Therefore, especially vulvar melanoma patients should be screened for activating KIT mutations.

Lack of Correlation Between Immunohistochemical Expression of CKIT and KIT Mutations in Atypical Acral Nevi

Given the correlation between KIT mutations and immunohistochemical expression of CKIT in acral melanoma, our aim was to confirm the utility of CKIT detection as a screening tool for KIT genotyping in atypical acral nevi and to ascertain the frequency of KIT mutations in the same. Immunohistochemical staining for CKIT was performed and staining criteria were the following: negative = <10%, 1 = 11%-49%, and 2 = >50% of cells. Intensity grading was as follows: negative = 0, weak = 1, moderate = 2, and strong = 3. Genomic amplification was performed on KIT exons commonly mutated in acral melanomas (11, 13, and 17) from atypical acral nevi (23) ranging in severity from mild (9), moderate (10), and severe (4). The control group included acral nevi without atypia (19). For purposes of statistical analyses, cases with 11% or more staining of cells were compared with negative cases and cases with a staining intensity of 1 or higher were compared with the negatives. Immunohistochemical analyses revealed the following: positive staining with an intensity 1 or more in 18 of 22 (82%) of cases with atypia (5 mild; 9 moderate and 4 severe) and in 13 of 17 (76%) nevi without atypia with no statistically significant differences between both groups. Genomic analyses of exon regions revealed no abnormalities in "hotspots" frequently associated with point mutations in acral melanomas. Our findings indicate a lack of correlation between immunohistochemical expression of CKIT and KIT mutations in atypical acral nevi. Atypical acral nevi do not exhibit genetic alterations in KIT associated with acral melanomas.

KIT Pathway Alterations in Mucosal Melanomas of the Vulva and Other Sites

A significant proportion of mucosal melanomas contain alterations in KIT. The aim of this study was to characterize the pattern of KIT, NRAS, and BRAF mutations in mucosal melanomas at specific sites and to assess activation of the KIT downstream RAF/MEK/extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/AKT pathways in mucosal melanoma specimens. Seventy-one primary mucosal melanomas from various sites were studied. Mutation analysis was done by DNA sequencing. Expression of KIT, phosphorylated (p)-ERK, and p-AKT was evaluated by immunohistochemistry. KIT mutations were detected in 35% (8 of 23) of vulvar, 9% (2 of 22) of anorectal, 7% (1 of 14) of nasal cavity, and 20% (1 of 5) of penile melanomas. No KIT mutations were found in 7 vaginal melanomas. The difference in KIT mutation frequency between vulvar and nonvulvar cases was statistically significant (P = 0.014). The overall frequencies of NRAS and BRAF mutations were 10% and 6%, respectively. Notably, vaginal melanomas showed a NRAS mutation rate of 43%. KIT gene amplification (≥4 copies), as assessed by quantitative real-time PCR, was observed in 19% of cases. KIT expression was associated with KIT mutation status (P < 0.001) and was more common in vulvar than nonvulvar tumors (P = 0.016). Expression of p-ERK and p-AKT was observed in 42% and 59% of tumors, respectively, and occurred irrespective of KIT/NRAS/BRAF mutation status. NRAS mutation was associated with worse overall survival in univariate analysis. Results show that KIT mutations are more common in vulvar melanomas than other types of mucosal melanomas and that both the RAF/MEK/ERK and PI3K/AKT pathways are activated in mucosal melanoma specimens.

Highlights of This Issue

Metformin is a widely-used antidiabetic drug whose anticancer effects represent a promising and novel approach for the treatment of cancer. Chemotherapy produces genotoxic stress and induces p53 activity, which can cross-talk with the AMPK/mTOR pathway. Rocha and colleagues tested the combination of metformin and paclitaxel and showed that combined treatment is more effective at arresting cells in the G2/M phase of the cell cycle, decreasing tumor growth, and increasing apoptosis in tumor-bearing mice. These results demonstrate that different drugs may cooperate to increase anti-growth signals and suggest that activation of AMPK may be an alternative therapeutic strategy in cancer treatment.Important advances have been made recently in the treatment of prostate cancer, with several drugs for metastatic, castration-resistant prostate cancer obtaining FDA approval in 2010 and 2011. In this issue of CCR Focus, guest editors Gerhardt Attard and Johann de Bono discuss the recent progress that has been made in prostate cancer therapy. Topics covered include targeting continued androgen receptor signaling; immunotherapeutic approaches in prostate cancer; the use of circulating tumor cells as treatment response biomarkers; and overcoming chemotherapy resistance in prostate cancer. Particular emphasis is put on the impact of newly approved agents (abiraterone, sipuleucel-T, and cabazitaxel).Bone metastases are ultimately responsible for the death of 500,000 patients worldwide every year. Investigators have been unable to study the molecular events underlying bone metastasis in these patients because of the lack of quality tissue available for study. Here, Mehra and colleagues present the discovery of nonossified bone metastases from multiple patients with advanced prostate cancer and their subsequent characterization and comparison to nonosseous metastases from the same patients. This represents a versatile and practical approach that may be used to characterize the steps in metastasis and opens important new possibilities for clinical monitoring through biomarker evaluation during treatment.KIT is an important oncogene in mucosal melanoma. In this issue, Omholt and colleagues studied mucosal melanomas from several different anatomical sites and found a significantly higher frequency of KIT mutations in melanomas of the vulva compared with melanomas of other mucosal sites (35% versus 10%). Using immunohistochemistry, the authors also found that ERK and AKT were activated in a large proportion of mucosal melanoma samples. Targeting the KIT downstream RAF-MEK-ERK and PI3K-AKT signaling pathways may represent a promising alternative therapeutic approach in mucosal melanoma, especially in the subset of tumors lacking activating KIT mutations.

Aberrations of KIT, BRAF, NRAS, and PDGFRA in Chinese melanoma patients and their significance: Large, scale analysis of 644 patients.

8568 Background: Mutations in KIT, BRAF, NRAS and PDGFRA are common in melanoma, which have not been extensively studied in Asia. We examined these aberrations and correlated the aberrations to the clinical features and survival in Asian melanoma patients. Methods: This study involved samples from 644 melanoma patients in Peking University Cancer Hospital. Clinical data were collected. Tissue samples were analyzed for mutations in KIT (exons 9,11,13,17,18), BRAF (exons 11,15), NRAS (exons1,2) and PDGFRA (exons 12,14,18) genes by PCR amplification and Sanger sequencing. The copy numbers of KIT gene were analyzed by quantitative PCR. Results: The incidence of somatic mutations within the KIT, BRAF, NRAS and PDGFRA genes was 10.1% (58/573), 25.9% (121/468), 7.2% (33/459) and 4.8% (17/352), respectively. The incidence of increased KIT copy number was 7.6% (39/516). The highest KIT mutation frequency is within the CSD subgroup (27.3%, 9/33). Increased KIT gene copy number was comparatively more frequent in acral (8.0%, 14/176) and mucosal (11.5%, 17/148) melanomas than in CSD (3.2%, 1/31) and Non-CSD (1.9%, 2/104) melanomas. Surprisingly, BRAF mutations were detected in 17.9% (28/156) of acral melanomas and 12.5% (16/128) of mucosal melanomas. The most frequent mutation in BRAF was V600E (87.3%). The median follow-up period was 24 (3~229) months (n=473). No statistical differences were found for thickness and ulceration rates between melanomas with or without these mutations (P=0.6). The median survival for patients with KIT mutations (30 months) and BRAF (33m) were significantly shorter than for patients with WT tumors (53m; P=0.01, P=0.005 respectively). Overall survivals were similar in groups with or without NRAS and PDGFRA mutations. Conclusions: KIT and BRAF are important oncogenes in Asian melanomas. Mutations in the BRAF gene were more common than KIT mutations. For the first time, our study suggests that genetic KIT and BRAF aberration is an adverse prognostic factor for melanoma. These results suggest that the KIT inhibitor as well as BRAF V600E inhibitor might play their roles in Asian melanoma patients. Supported by the National Natural Science Foundation of China30973483.

Mutations in KIT occur at low frequency in melanomas arising from anatomical sites associated with chronic and intermittent sun exposure

In melanoma, mutations in KIT are most frequent in acral and mucosal subtypes and rarely reported in cutaneous melanomas particularly those associated with intermittent UV exposure. Conversely melanomas arising within chronic sun damaged skin are considered to harbour KIT mutations at higher rates. To characterize the frequency of KIT mutations in a representative melanoma population, 261 patients from two Australian melanoma centres were prospectively screened for mutations in exons 11, 13 and 17 of the KIT gene. A total of 257 patients had cutaneous melanoma arising from non-acral sites and four were acral melanomas. No mucosal or ocular melanomas were analysed. KIT mutations were identified in five tumours (2% of the entire cohort) including two acral melanomas. Two of the three non-acral melanomas with KIT mutations were associated with markers of chronic sun damage as assessed by the degree of skin elastosis. In the remaining cohort, 43% had chronically sun damaged skin. This report confirms that within an Australian population, KIT mutations are infrequent in cutaneous melanomas associated with both intermittent and chronic sun exposed skin.

KIT gene mutations and copy number in melanoma subtypes.

We recently identified a KIT exon 11 mutation in an anorectal melanoma of a patient who had an excellent response to treatment with imatinib. To determine the frequency of KIT mutations across melanoma subtypes, we surveyed a large series of tumors. One hundred eighty-nine melanomas were screened for mutations in KIT exons 11, 13, and 17. KIT copy number was assessed by quantitative PCR. A subset of cases was evaluated for BRAF and NRAS mutations. Immunohistochemistry was done to assess KIT (CD117) expression. KIT mutations were detected in 23% (3 of 13) of acral melanomas, 15.6% (7 of 45) of mucosal melanomas, 7.7% (1 of 13) of conjunctival melanomas, 1.7% (1 of 58) of cutaneous melanomas, and 0% (0 of 60) of choroidal melanomas. Almost all the KIT mutations were of the type predicted to be imatinib sensitive. There was no overlap with NRAS mutations (11.1% of acral and 24.3% of mucosal tumors) or with BRAF mutations (absent in mucosal tumors). Increased KIT copy number was detected in 27.3% (3 of 11) of acral and 26.3% (10 of 38) of mucosal melanomas, but was less common among cutaneous (6.7%; 3 of 45), conjunctival (7.1%; 1 of 14), and choroidal melanomas (0 of 28). CD117 expression, present in 39% of 105 tumors representing all melanoma types, did not correlate with either KIT mutation status or KIT copy number. Our findings confirm that KIT mutations are most common in acral and mucosal melanomas but do not necessarily correlate with KIT copy number or CD117 expression. Screening for KIT mutations may open up new treatment options for melanoma patients.

Gain-of-Function Mutations in the Extracellular Domain of KIT Are Common in Canine Mast Cell Tumors

In the current study, we examined the types and frequency of KIT mutations in mast cell tumors from 191 dogs. Sequencing of reverse transcription-PCR products revealed alterations in 50 (26.2%) of the dogs. Most mutations were in exon 11 (n = 32), and of these, most were internal tandem duplications (n = 25) between residues 571 and 590. Within exon 11, there were two hotspots for mutations at codons 555-559 and 571-590. In addition, nine dogs had mutations in exon 8 and eight had mutations in exon 9. We selected the two most common mutants and two representative exon 11 mutants for further analysis. When expressed in Ba/F3 cells, they were constitutively tyrosine phosphorylated and induced growth factor-independent cell proliferation. AG1296, a tyrosine kinase inhibitor, dose dependently inhibited both the tyrosine phosphorylation of these mutants and their induction of growth factor-independent proliferation. This study shows that activating mutations in not only exon 11 but also exons 8 and 9 are common in canine mast cell tumors. These results also show that Ba/F3 cells can be used for the direct characterization of canine KIT mutants, eliminating the need to make equivalent mutations in the mouse or human genes.

Somatic KIT mutations occur predominantly in seminoma germ cell tumors and are not predictive of bilateral disease: Report of 220 tumors and review of literature

Mutations in the KIT gene occur in approximately 8% of all testicular germ cell tumors (TGCT) and KIT is the most frequently mutated known cancer gene. One report has shown that 93% of patients with bilateral disease have a mutation at codon 816 of the KIT gene. Importantly, this suggests that the identification of a mutation in KIT is predictive of the development of a contralateral TGCT. We investigated the frequency and type of mutations in KIT in a series of 220 tumors from 211 patients with TGCTs and extragonadal germ cell tumors. In 170 patients with unilateral TGCT and no additional germ cell tumour, we identified one exon 11 mutation in a patient with unilateral TGCT and eight activating KIT mutations in exon 17 (9/175, 5.1%). In 32 patients with bilateral TGCT, one patient had an activating KIT mutation in exon 17 (3.1%). The incidence of activating KIT mutations in sporadic TGCT vs. familial TGCT was not significantly different. All mutations were identified in seminomas. Three extragonadal primary germ cell tumors were examined and in one tumor an activating KIT mutation was demonstrated in the pineal germinoma. Interestingly, this mutation was also seen in the patient's testicular seminoma. We find no evidence for an increased frequency of KIT mutations in bilateral TGCT.