You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
despite the advancement in targeted therapy , treatment of cancer still remains as a huge unmet medical need .
multiple factors , in addition to the complexity of cancer biology , contribute to this unsatisfactory state .
such close tumor - host interactions are vitally important in determining the sensitivity of tumor cells to cancer treatments .
however , such complex tumor context is not replicated either in vitro or in vivo in transgenic or xenograft models .
genetically engineering mouse tumor models provide a potentially promising alternate to assess preclinical cancer drug efficacy .
near 30% of the 98 000 clinical trials listed on clinicaltrials.gov were related to cancer drugs .
such a large number not only reflects the huge unmet medical needs , but also stems from the low success rate of cancer medicine development .
it is estimated that only 10% of the cancer drug candidates entering clinical stage ultimately gain market approval .
new trial approaches are urgently needed especially for the development of targeted cancer therapies that will only benefit a subset of patients .
prospectively identifying sensitive or excluding resistant patient populations to achieve definitive clinical benefit led to successful development of several targeted therapies .
such successes include the use of her2 fluorescent in situ hybridization ( fish ) assay for selecting her2-positive breast cancer patients receiving herceptin treatment , egfr mutation assay for selecting non - small cell lung cancer patients to be treated with gefitinib / erlotinib , and applying kras mutation assay to avoid exposing colorectal cancer patients with kras mutations to anti - egfr mabs .
recently , such biomarker - based prospective patient selection strategy was applied to phase 1 studies to expedite clinical development of several new targeted agents .
overall response rates from 50% to near 80% were achieved in early phase trials of crizotinib ( alk inhibitor ) , as well as plx-4032 ( r7204 ) and gsk2118436 ( braf v600e inhibitors ) .
such dramatic early efficacy data prompted sponsors launching phase 3 registration trials based on phase 1 and phase 2 results ( table 2 ) .
for compounds lacking definitive biomarkers for identifying sensitive / resistant subpopulation , adaptive trial design to incorporate biomarker identification and validation into one single trial may represent an effective and efficient approach .
bla , biologic license application ; cml , chronic myeloid leukemia ; ctla4 , cytotoxic t - lymphocyte protein 4 ; egfr , epidermal growth factor receptor ; gist , gastrointestinal stromal tumor ; her2 , human epidermal growth factor receptor 2 ( also known as erbb2 ) ; hsp90 , heat - shock protein , 90 kda ; igfr1 , insulin - like growth factor receptor 1 ; mcl1 , myeloid cell leukemia sequence 1 ; mtor , mammalian target of rapamycin ; nda , new drug application ; nsclc , non - small cell lung cancer ; parp1 , poly ( adp - ribose ) polymerase 1 . sources : company reports , clinicaltrials.gov , american society of clinical oncology , american society of hematology .
the redundancy in the signaling systems at the disposal of the cancer cells often render individual targeted agents inactive in treating most cancers . even in rare exceptions , such as narrowly defined patient populations , single agent activities could be dramatic , but cancers still recur .
combinations of targeted agents represent a potentially effective approach to simultaneously inhibiting multiple pathways , suppressing feedback reactivation of compensatory signaling network , and therefore to prevent recurrence .
the parallels between clinical development of combinations and understanding of cancer resistance will ultimately lead to personalized medicine , such as matching targeted therapy with cancer patients based on molecular events underlying their malignancies .
such close tumor - host interactions are vitally important in determining the sensitivity of tumor cells to cancer treatments .
however , such complex tumor context is not replicated either in vitro or in vivo in transgenic or xenograft models .
genetically engineering mouse tumor models provide a potentially promising alternate to assess preclinical cancer drug efficacy .
near 30% of the 98 000 clinical trials listed on clinicaltrials.gov were related to cancer drugs .
such a large number not only reflects the huge unmet medical needs , but also stems from the low success rate of cancer medicine development .
it is estimated that only 10% of the cancer drug candidates entering clinical stage ultimately gain market approval .
new trial approaches are urgently needed especially for the development of targeted cancer therapies that will only benefit a subset of patients .
prospectively identifying sensitive or excluding resistant patient populations to achieve definitive clinical benefit led to successful development of several targeted therapies .
such successes include the use of her2 fluorescent in situ hybridization ( fish ) assay for selecting her2-positive breast cancer patients receiving herceptin treatment , egfr mutation assay for selecting non - small cell lung cancer patients to be treated with gefitinib / erlotinib , and applying kras mutation assay to avoid exposing colorectal cancer patients with kras mutations to anti - egfr mabs .
recently , such biomarker - based prospective patient selection strategy was applied to phase 1 studies to expedite clinical development of several new targeted agents .
overall response rates from 50% to near 80% were achieved in early phase trials of crizotinib ( alk inhibitor ) , as well as plx-4032 ( r7204 ) and gsk2118436 ( braf v600e inhibitors ) .
such dramatic early efficacy data prompted sponsors launching phase 3 registration trials based on phase 1 and phase 2 results ( table 2 ) .
for compounds lacking definitive biomarkers for identifying sensitive / resistant subpopulation , adaptive trial design to incorporate biomarker identification and validation into one single trial may represent an effective and efficient approach .
bla , biologic license application ; cml , chronic myeloid leukemia ; ctla4 , cytotoxic t - lymphocyte protein 4 ; egfr , epidermal growth factor receptor ; gist , gastrointestinal stromal tumor ; her2 , human epidermal growth factor receptor 2 ( also known as erbb2 ) ; hsp90 , heat - shock protein , 90 kda ; igfr1 , insulin - like growth factor receptor 1 ; mcl1 , myeloid cell leukemia sequence 1 ; mtor , mammalian target of rapamycin ; nda , new drug application ; nsclc , non - small cell lung cancer ; parp1 , poly ( adp - ribose ) polymerase 1 . sources : company reports , clinicaltrials.gov , american society of clinical oncology , american society of hematology .
the redundancy in the signaling systems at the disposal of the cancer cells often render individual targeted agents inactive in treating most cancers . even in rare exceptions , such as narrowly defined patient populations , single agent activities could be dramatic , but cancers still recur .
combinations of targeted agents represent a potentially effective approach to simultaneously inhibiting multiple pathways , suppressing feedback reactivation of compensatory signaling network , and therefore to prevent recurrence .
the parallels between clinical development of combinations and understanding of cancer resistance will ultimately lead to personalized medicine , such as matching targeted therapy with cancer patients based on molecular events underlying their malignancies .
the already saturated clinical trial density in well established oncology trial regions such as north america and western europe poses an impassable challenge to accruing patients with proper molecular characteristics to match targeted agents .
for example , nearly 7 000 patients need to be screened to identify the 5% patients with tumors harboring the eml4-alk fusion event for the crizotinib phase 3 trial of 320 patients . the success in contributing patients to the i - pass trial is a beginning for china to play a more active role in global development of new anti - cancer agents . in preparation for this new era , it is vital for investigators in china to master the knowledge in new cancer biology , pharmacokinetics , pharmacodynamics , innovative trial design of both early and late phases , as well as to establish core capabilities in molecular testing of tumor samples in real time fashion to support prospective patient selection . in collaboration with us chinese anti - cancer association ( uscaca ) , chinese journal of cancer has organized a series of review articles to cover a broad spectrum of topics in targeted cancer therapies .
these articles will analyze each major pathway or target class with an emphasis on mechanism of action , translational medicine , and clinical development .
this series of reviews will provide a basis for our readers , especially clinical investigators , to develop a comprehensive appreciation of these targets and pathways in cancer as well as relevant targeted therapies being developed .
with unprecedented understanding of molecular events underlying human cancer in this genomic era , a large number of drugs specifically targeting hypothesized oncogenic drivers to which tumors are potentially addicted to have been developed and continue to be developed . 
 these targeted cancer therapies are being actively tested in clinical trials with mixed successes . 
 this editorial provides an overview on successful targeted cancer drugs on the market and those drugs that are in late clinical development stages . 
 importantly , the article lays out main challenges in developing molecular targeted therapies and potential path forward to overcome these challenges , as well as opportunities for china in this new era of targeted agents . 
 the editorial serves as an introduction to the targeted cancer therapies series that will review in depth of major pathways and drugs targeting these pathways to be published in the coming issues of the chinese journal of cancer .