to the surprise and deep disappointment of all involved in the treatment of lung cancer , several large trials did not demonstrate any benefit of tyrosine kinase inhibitors ( tkis ) as an addition to chemotherapy [ 13 ] . basic and clinical research then focused on mutations of the gene for epidermal growth factor receptor ( egfr ) as a predictive factor for response to monotherapy with tkis and to development of new compounds with broader and/or irreversible inhibition .   the biological basis for the negative experience with combined treatment gefitinib and erlotinib met all three standard criteria for inclusion in a combination with chemotherapy : activity as monotherapy , different mechanism of action , and different toxicity . why , then , did the combination not work ? as explained in a recent editorial , we believe that the cells of tumors sensitive to tkis are pushed into the g-0 phase of the cell cycle and therefore become resistant to cytotoxic drugs . if antagonism between the two classes of drugs is really the biological basis for the aforementioned negative experience , then an optimal combination of tkis and chemotherapy should be in an intermittent , rather than a continuous schedule . this brief report presents a single - institution experience on intermittent chemotherapy and tki in a small series of patients with advanced adenocarcinoma of the lung . our hypothesis was that intermittent treatment would lead to superior time to progression , when compared to experience with chemotherapy alone . if confirmed , such a result would be a solid basis for a randomised clinical trial . patients eligible for the trial were chemonave with microscopically confirmed adenocarcinoma of the lung , had stage iii b ( wet ) or iv according to uicc - tnm classification ( 6th edition ) , had smoking history of less than 10 packs in years , had an ecog performance status 0 or 1 , and had adequate parameters of hematological , liver , and renal function to receive cisplatin - based chemotherapy . in the absence of neurological symptoms , patients with brain metastases were eligible and were treated with brain irradiation only in case of intracranial progression . all patients had their diagnosis confirmed by biopsy or cytology . at the time when the trial was initiated , testing for egfr mutations was not available . within three weeks prior to treatment , the precise extent of the disease was determined by chest x - ray and ct scanning of the chest , upper abdomen , and brain . since 2008 , pet - ct scanning has been available and included in the initial diagnostics and in followup . the treatment started with four cycles of intermittent chemotherapy and erlotinib according to the following schedule : day 1 : gemcitabine 1250  mg / m in 30-minute infusion , day 2 : cisplatin 75  mg / m , with appropriate hydration and antiemetics , day 4 : gemcitabine 1250  mg / m in 30-minute infusion , days 515 : erlotinib 150  mg daily p.o . the number of cycles depended on tolerance to cisplatin - based chemotherapy and was determined individually . immediately after the last cycle , patients continued with erlotinib 150  mg / m daily continuously until progression or unacceptable toxicity . definition of complete response ( cr ) , partial response ( pr ) , stable disease ( sd ) , and progression followed the recist criteria . the first evaluation of response was done during the third cycle of intermittent therapy , with confirmation of response during the fifth cycle . control radiological examinations were repeated every 2 months for chest x - ray , every 4 months for ct , and at 6 and 12 months for pet - ct ( only patients who had this examination during their initial diagnostics ) . in october 2010 , all biopsy samples were reviewed , and specimens with more than 10% of tumour tissue were analyzed . genomic dna was extracted from formalin - fixed , paraffin - embedded tissue sections using qiaamp dna ffpe tissue kit ( qiagen , hilden , germany ) according to the manufacturer 's instructions . quantification of extracted dna was done on qubit fluorometer ( invitrogen , carlsbad , usa ) . to detect egfr gene - activating mutations , we used therascreen egfr29 mutation kit ( dxs diagnostics , qiagen , manchester , uk ) . all realtime pcr reactions were performed in a 25  l final volume on abi 7500 instrument ( applied biosystems , carlsbad , usa ) . after standard chemotherapy for metastatic nonsmall cell carcinoma , the expected ttp is 5 months . the size of this single - arm nonrandomised trial of intermittent therapy was based on the assumption of 9 months as the median time to progression ( ttp ) . to obtain such a result with a confidence interval of 612 months , we planned to recruit 40 patients . the investigators strictly followed recommendations of the helsinki declaration ( 1964 , with later amendments ) and of the european council convention on protection of human rights in bio - medicine , as accepted in oviedo in 1997 . the protocol was approved by the institutional review board ( institute of oncology , ljubljana ) and by the national committee for medical ethics , ministry of health , republic of slovenia . one patient was later found to have metastatic carcinoma of the pancreas rather than primary lung cancer and was excluded from all further analyses .   with 12 patients each , twelve patients were never - smokers , and most were in good general condition ( ps 0 - 1 for 21 patients ) . with the exception of a single patient with  wet bone metastases were the most common site of metastatic disease , followed by pleura / pericardium , contralateral lung metastases , and liver . two or more sites of metastatic disease were documented in 4 and 12 patients , respectively ( table 1 ) . three patients had only cytological diagnosis , and an additional 3 had biopsy samples too small to allow for analysis of egfr mutations in tumor cells . of the 18 adequate samples , 8 were positive for egfr gene - activating mutations . the actual number of cycles of intermittent therapy was from 1 to 6 cycles ( median : 4 cycles ) . due to early progression , 7 patients were still on maintenance treatment with erlotinib , and an additional patient stopped treatment with erlotinib after 12 months in pet - ct confirmed complete remission ( figures 1 and 2 ) . for the remaining patients , median total duration of treatment was 10 months . during the initial phase , side effects of maintenance with erlotinib were skin toxicity ( grade 3 : 1  pt ; grade 2 : 11  pts ) and diarrhea ( grade 2 in 1  pt ) . all patients are evaluable for response , and no patient has been lost to followup . for the whole group of 24 patients , complete remission ( cr ) was seen in 5 pts ; partial remission ( pr ) in 9  pts ( response rate 58% ) , minimal response or stable disease ( sd ) in 8  pts , and progression in 2  pts . a clear and statistically significant ( p < .05 ) correlation was seen between the presence of activating egfr mutations and response . among the 8 patients who were positive for egfr gene - activating mutations , 4 complete and no cr and only 2 pr were seen among the 10 patients negative for mutations ( table 2 ) . for the whole group , median time to progression ( ttp ) was 13.4 months , and median overall survival ( os ) was 23 months . median ttp and os for this group was 21.5 months and 24.2 months , respectively . for patients without egfr mutations , ttp was 5 months , and os was 7 months ( table 2 and figures 3 and 4 ) . this clinical trial was launched at a time when routine testing for egfr gene - activating mutations was not yet available . selection of patients for a combination of chemotherapy and erlotinib was made on the basis of classical histopathology ( adenocarcinoma ) and smoking status . since testing for egfr gene mutations is now available , it is clear that patients with activating mutations are those who really benefit from tkis . in addition , standard first - line treatment for patients with activating egfr mutations is now monotherapy with a tki [ 6 , 7 ] . since continuing a trial with the same selection criteria and without considering the status of egfr gene activating mutations was not justified , the research group made a decision to close the trial and analyse the experience . in order to get a longer interval for intermittent erlotinib , gemcitabine was given on days 1 and 4 of the cycle . when compared to the standard day 1 and day 8 schedule , this minor modification in timing of cytotoxic drugs did not have any adverse effect on the tolerance to treatment . clearly , other platin - based schedules which apply chemotherapy on a 3-weekly basis ( such as pemetrexed - cisplatin or paclitaxel - carboplatin ) can offer an even longer interval for tkis and might be considered for future trials of intermittent treatment . two other groups recently reported promising experience with intermittent chemotherapy and tkis . in a trial from the usa , two schedules of intermittent treatment were tested . in combination with pemetrexed ( 500  mg / m on day 1 ) , erlotinib was given either as a pulse application in a high dose ( range : 800 to 1400  mg ) given on days 2 , 9 and 16 , or in lower doses ( 150250  mg daily ) on days 2 to 16 . while tolerance to this treatment was good , the small number and heterogeneity of patients recruited into this trial do not allow for any clear conclusion regarding the effectiveness of intermittent treatment . of more importance this study from asia compared gemcitabine and either cisplatin or carboplatin to a schedule with addition of intermittent application of erlotinib ( 150  mg on days 14 to 28 of the cycle ) and reported significantly superior ttp with the intermittent schedule . their experience is most valuable but may not be of direct relevance for the rest of the world , due to the well - known differences in sensitivity of lung cancer to tkis between asian and caucasian patients .   despite its small size , our trial can offer valuable experience for further research on optimisation of treatment with combinations of chemotherapy and tkis . looking at the whole series of patients , we can conclude that intermittent chemotherapy and erlotinib is a treatment of very low toxicity . it is also clear that the efficacy of treatment is closely related to the presence or absence of egfr gene - activating mutations . the most important finding is the excellent response rate with a substantial proportion of complete responses and prolonged ttp and os for patients positive for egfr gene - activating mutations . for many years , the maximal expectation of a patient with metastatic nonsmall cell lung cancer was a partial remission of relatively short duration in the range of 5 to 9 months . with intermittent treatment , while the number of patients in our trial is small and any definitive conclusion would be premature , we nevertheless believe that further research of intermittent therapy for patients positive for egfr gene - activating mutations is warranted . a randomised trial comparing first - line tki as monotherapy to the intermittent schedule should clarify the real value of this new approach .
background . intermittent application of chemotherapy and tyrosine kinase inhibitors may avoid antagonism between the two classes of drugs . 
 this hypothesis was tested in a phase ii clinical trial . 
 patients and methods . 
 eligible patients were nonsmokers or light smokers , chemo - nave , with metastatic adenocarcinoma of the lung . 
 treatment : 4 to 6 cycles of gemcitabine 1250  mg / m2 on days 1 and 4 , cisplatin 75  mg / m2 on day 2 , and erlotnib 150 mg daily on days 515 , followed by erlotinib as maintenance . results . 
 24 patients entered the trial . 
 four pts had grade 3 toxicity . 
 complete remission ( cr ) and partial remission ( pr ) were seen in 5  pts and 9  pts , respectively ( response rate 58% ) . 
 median time to progression ( ttp ) was 13.4 months and median overall survival ( os ) was 23 months . when compared to patients with negative or unknown status of egfr mutations , 
 8 patients with egfr gene activating mutations had significantly superior experience : 4 cr and 4 pr , with median ttp 21.5 months and os 24.2 months ( p < .05 ) . conclusions . 
 intermittent schedule with gemcitabine , cisplatin and erlotinib has mild toxicity . for patients who are positive for egfr gene activating mutations 
 , this treatment offers excellent response rate , time to progression and survival .