gliomas are the most common primary brain tumors in adults and are usually classified and graded according to the world health organisation ( who ) . currently , chemotherapy is standard of care for all diffuse gliomas , either at first diagnosis or at first recurrence [ 15 ] . treatment options for patients failing radiotherapy and a first line of alkylating or methylating chemotherapy are limited . the cytotoxic effect of tmz is mediated primarily via methylation at the o position of guanine . one of the main mechanisms of tumor resistance to tmz is thought to be mediated by o - methylguanine - dna methyltransferase ( mgmt ) . evidence supporting this role of mgmt comes from clinical studies indicating that hypermethylation of the promoter of mgmt is associated with improved tumor response and survival in patients with gbm [ 7 , 8 ] . because of the more continuous exposition with ddtmz it has been assumed that dose dense temozolomide ( ddtmz ) schedules could overcome mgmt dependent resistance against tmz by a more effective depletion of deplete intracellular levels of the dna repair enzyme , mgmt . studies using ddtmz show it is well tolerated and generally safe , also when given in higher monthly doses and in patients who have previously received tmz [ 1018 ] . we used the 1  week on/1  week off tmz regimen ( ddtmz ) for patients with relapsing gbm or other glioma after prior tmz or nitrosourea chemotherapy to study the efficacy and toxicity of ddtmz in heavily pre - treated patients with high - grade glioma . data of all diffuse glioma patients treated with ddtmz after prior chemotherapy in our center were retrospectively collected . patients were included in this study if they had a histologically confirmed low - grade glioma or high - grade glioma , with a progressive and measurable enhancing tumor on the mri ( diameter > 2  cm ) , relapsing after prior radiotherapy and at least one line of chemotherapy , and had concluded rt at least 3  months prior to the diagnosis of progression . we collected data about patient characteristics , tumor characteristics , prior treatment , number of ddtmz cycles , use of dexamethason , adverse effects , reason of discontinuation , and further treatments . according to histology three categories of patients were distinguished : patients treated with ddtmz for a progressive primary gbm after radiotherapy and tmz ( group a ) ; patients with recurrent astrocytoma who grade 2 or 3 ( group b ) , or recurrent oligo - astrocytoma who grade 2 or 3 , without 1p and 19q loss ; and patients with progressive who grade 2 or 3 oligodendroglioma or oligo - astrocytoma with 1p and 19q loss ( group c ) . who grade 2 tumors were combined with who grade 3 tumors because all patients had contrast enhancing lesions on the mri scan at the time of treatment with ddtmz , suggesting malignant dedifferentiation of the who grade 2 tumors . furthermore , a previous study with tmz in recurrent who grade 2 astrocytoma , with enhancement on the mri - scan , at our institution has shown similar results to the pilot trial of tmz in recurrent who grade 3 gliomas ( pfs at 12  months 25% vs. 24% ) . [ 3 , 4 ] . patients received tmz on day 17 and on day 1521 of a 28-day cycle for up to 12 cycles or until documented disease progression or unacceptable toxicity . the starting dose of the tmz was 100  mg / m / day . in the absence of toxicity or only ctcae grade 1 toxicity during the first two treatment weeks the dose was escalated , in two steps to dose level 1 ( 150  mg / m / day ; table  1 for dose levels ) . toxicity was evaluated according to the common terminology criteria for adverse events ( ctcae ; version 3.0 ) . in case of hematological toxicity grade 4 or non - hematological toxicity grade 3 , the dosage tmz of the next cycle was reduced with 1 dose level . in case of ctcae grade 4 non - hematological toxicity , 4 hematological toxicity or a grade 3 non - hematological toxicity at dose level 4 ( 75  mg / m / day ) , the patient went off treatment . in case of dose reductions , blood examinations were done on day 15 and day 29 and when platelets were above 100 * 10/l and neutrophils counts above 1.5 * 10/l , the following 7  days tmz was administered . otherwise treatment was postponed until recovery to ctcae grade 1 and/or platelets were above 100 * 10/l . the treatment was stopped if it had to be postponed for more than 2  weeks.table  1dose levels of dose dense temozolomidedose leveldaily temozolomide dose ( mg / m / day)dose temozolomide per cycle ( mg / m)1150210021251750310014004751050 dose levels of dose dense temozolomide the objectives of the study were the assessment of progression free survival at 6 ( pfs-6 ) and 12 ( pfs-12 ) months , objective response rate ( orr ) , overall survival ( os ) , and toxicity . os was calculated from the start of the tmz treatment to the date of death . pfs was calculated from the start of the tmz until the date of progression or death . clinical evaluation was done every 4  weeks and mri was made every 12  weeks or in case of neurological deterioration . response to treatment was reviewed as part of this analysis ( w.t . ) . in this exploratory analysis , between june 2005 and june 2011 , 53 patients were treated with ddtmz for the progression of a glioma in our center . twenty - four patients were treated for a recurrent gbm ( group a ) , 16 patients were treated for a recurrence of a who grade 2 or 3 astrocytoma , oligodendroglioma , or oligo - astrocytoma , without combined 1p and 19q loss , with a contrast enhancing lesion on mri ( group b ) and 13 patients were treated for a recurrence of a who grade 2 or 3 oligodendroglioma or oligo - astrocytoma with combined 1p and 19q loss , with a contrast enhancing lesion on mri ( group c ) . all gbm patients progressed after chemo - irradiation with tmz , except for one patient who had progression after radiotherapy and during the 6th cycle of 1st line standard day 15 every 4  weeks schedule tmz chemotherapy . five gbm patients treated with chemo - irradiation progressed directly after six cycles of adjuvant tmz ; all other patients had a tmz free interval , before the start of ddtmz . six patients with a recurrent primary - gbm received a second line of therapy after chemo - irradiation : dendritic - cell therapy ( 1 ) , cediranib ( 1 ) , lomustine combined with cediranib ( 2 ) , and , imatinib combined with hydroxyurea ( 2).table  2characteristics of patients treated with dose dense temozolomide for a progressive glioma after radiotherapy and 1 or 2 lines of chemotherapycharacteristicall patientsno . ( % ) of patients , n  =  53group ano . ( % ) of patients , n  =  24group bno . ( % ) of patients , n  =  16group cno . ( % ) of patients , n  =  13age , years  median49524344  range3174317432613360sex  male38 ( 72%)14 ( 58%)13 ( 81%)11(85% )  female15 ( 28%)10 ( 42%)3 ( 19%)2 ( 15%)first symptom  epilepsy36 ( 68%)11 ( 46%)13 ( 81%)12 ( 92% )  other17 ( 32%)13 ( 54%)3 ( 19%)1 ( 8%)who - ps  015 ( 28%)6 ( 25%)5 ( 31%)4 ( 31% )  127 ( 51%)16 ( 67%)7 ( 44%)4 ( 31% )  211 ( 21%)2 ( 8%)4 ( 25%)5 ( 38%)who histology grade at first operation  210 ( 63%)6 ( 46% )  36 ( 37%)7 ( 54%)who world health organisation , ps performance scoregroup a patients with recurrent primary glioblastoma , group b patients with recurrent who grade 2 or 3 astrocytoma or oligodendroglioma or oligoastrocytoma without combined 1p and 19q loss and with a contrast enhancing lesion on mri , group c patients with recurrent who grade 2 or 3 oligodendroglioma or oligoastrocytoma with combined 1p and 19q loss and with a contrast enhancing lesion on mritable  3previous treatments of patients treated with dose dense temozolomide for a progressive glioma after radiotherapy and 1 or 2 lines of chemotherapycharacteristicall patientsno . ( % ) of patients , n  =  53group ano . ( % ) of patients , n  =  24group bno . ( % ) of patients , n  =  16group cno . ( % ) of patients , n  =  13ddtmz as 2nd line of chemotherapy40 ( 75%)19 ( 79%)11 ( 69%)10 ( 77%)ddtmz as 3nd line of chemotherapy13 ( 25%)5 ( 21%)5 ( 31%)3 ( 23%)second operation15 ( 28%)3 ( 13%)6 ( 38%)6 ( 46%)third operation1 ( 2%)001 ( 8%)time between start last rt and start ddtmz , median ( range ) in months24 ( 5197)19 ( 875)18 ( 5197)45 ( 1093)time between last chemotherapy and start ddtmz , median ( range ) in months10 ( 094)5 ( 067)13 ( 192)17 ( 194)prior 1st line treatment53 ( 100%)24 ( 100%)16 ( 100%)13 ( 100%)rt / tmz27 ( 51%)23 ( 96%)3 ( 19%)1 ( 8%)tmz6 ( 11%)1 ( 4%)5 ( 31%)0pcv20 ( 38%)08 ( 50%)12 ( 92%)prior 2nd line treatment13 ( 25%)5 ( 21%)5 ( 31%)3 ( 23%)rt / tmz1 ( 2%)01 ( 6%)0tmz5 ( 9%)03 ( 19%)2 ( 15%)pcv2 ( 4%)01 ( 6%)1 ( 8%)other5 ( 9%)5 ( 21%)00ddtmz dose dense temozolomide , rt radiotherapygroup a patients with recurrent primary glioblastoma , group b patients with recurrent who grade 2 or 3 astrocytoma or oligodendroglioma or oligoastrocytoma without combined 1p and 19q loss and with a contrast enhancing lesion on mri , group c patients with recurrent who grade 2 or 3 oligodendroglioma or oligoastrocytoma with combined 1p and 19q loss and with a contrast enhancing lesion on mri characteristics of patients treated with dose dense temozolomide for a progressive glioma after radiotherapy and 1 or 2 lines of chemotherapy who world health organisation , ps performance score group a patients with recurrent primary glioblastoma , group b patients with recurrent who grade 2 or 3 astrocytoma or oligodendroglioma or oligoastrocytoma without combined 1p and 19q loss and with a contrast enhancing lesion on mri , group c patients with recurrent who grade 2 or 3 oligodendroglioma or oligoastrocytoma with combined 1p and 19q loss and with a contrast enhancing lesion on mri previous treatments of patients treated with dose dense temozolomide for a progressive glioma after radiotherapy and 1 or 2 lines of chemotherapy ddtmz dose dense temozolomide , rt radiotherapy group a patients with recurrent primary glioblastoma , group b patients with recurrent who grade 2 or 3 astrocytoma or oligodendroglioma or oligoastrocytoma without combined 1p and 19q loss and with a contrast enhancing lesion on mri , group c patients with recurrent who grade 2 or 3 oligodendroglioma or oligoastrocytoma with combined 1p and 19q loss and with a contrast enhancing lesion on mri the median number of cycles of ddtmz was 4 ( range 112 ) , three patients completed 12 cycles . eight patients discontinued ddtmz because of toxicity : grade 4 thrombocytopenia ( 1 ) , persistent grade 2 or grade 3 fatigue ( 5 ) , grade 3 elevated transaminases ( 1 ) , and grade 3 allergic skin reaction ( 1 ) . five patients who stopped because of fatigue continued tmz in regular regimen of day 15 in a 28  day cycle and tolerated this well . in 25 patients , cd4 + lymphocytes counts were monitored ; 14 ( 56% ) of these patients developed a grade 3 cd4 + lymphopenia ( < 0.2 * 10/l ) and 6 ( 24% ) of these patients developed a grade 4 cd4 + lymphopenia ( < 0.05 * 10/l ) . two of the patients with a grade 4 cd4 + lymphopenia developed a pneumocystis carinii pneumonia , prior to routine monitoring of cd4 + counts , from which they fully recovered . the pfs-6 , the orr ( complete and partial response ) and median os for the three groups of patients are shown in table  4 . the median interval ( and range ) between the prior chemotherapy and the start of the ddtmz was 5  months ( 067  months ) in group a , 12.5  months ( range 192 ) in group b and 17  months ( range 194 ) in group c. the patients without 1p and 19q loss ( group a and b ) that started with the ddtmz within 3  months of the previous chemotherapy ( 12 out of 40 patients ) had a lower pfs-6 compared to the patients with a chemotherapy free interval of more than 3  months ( pfs-6 8% vs. 43% ; fisher exact test 0.033).table  4outcome of patients treated with dose dense temozolomide for a progressive glioma after radiotherapy and 1 or 2 lines of chemotherapyoutcomeall patientsn  =  53group an  =  24group bn  =  16group cn  =  13pfs-640%29%38%62%pfs-1213%13%13%15%median os9  months6  months9  months19  monthscr  +  pr17%8%19%33% ( 4:12)pfs-6 progression free survival at 6  months , pfs-12 progression free survival at 12  months , os overall survival , cr complete response , pr partial responsegroup a patients with recurrent primary glioblastoma , group b patients with recurrent who grade 2 or 3 astrocytoma or oligodendroglioma or oligo - astrocytoma without combined 1p and 19q loss and with a contrast enhancing lesion on mri , group c patients with recurrent who grade 2 or 3 oligodendroglioma or oligo - astrocytoma with combined 1p and 19q loss and with a contrast enhancing lesion on mri outcome of patients treated with dose dense temozolomide for a progressive glioma after radiotherapy and 1 or 2 lines of chemotherapy pfs-6 progression free survival at 6  months , pfs-12 progression free survival at 12  months , os overall survival , cr complete response , pr partial response group a patients with recurrent primary glioblastoma , group b patients with recurrent who grade 2 or 3 astrocytoma or oligodendroglioma or oligo - astrocytoma without combined 1p and 19q loss and with a contrast enhancing lesion on mri , group c patients with recurrent who grade 2 or 3 oligodendroglioma or oligo - astrocytoma with combined 1p and 19q loss and with a contrast enhancing lesion on mri in this group of 53 chemotherapy and radiotherapy pre - treated gliomas , ddtmz showed activity . although this is a retrospective study with a limited sample size , our results are also comparable to other studies on dose - dense tmz in recurrent gliomas [ 1217 ] . however , in all our groups the observed activity is well within the range of previous reports on standard dosing tmz . the pfs-6 of 29% ( 95%-ci 1147% ) ( table  4 ; group a ) in gbm is within the range of the pivotal standard dose phase ii tmz trials in recurrent gbm . ( pfs-6 : 1924% ) [ 2123 ] more in particular , brandes et al . described a 24% ( 95% ci 1442% ) for 2nd line standard dosing tmz in recurrent gbm . the results in group b ( recurrent who grade 2 or 3 astrocytoma or oligodendroglioma without 1p and 19q loss ) are comparable to the 2nd line results in the pivotal phase 2 trial in recurrent anaplastic astrocytoma or anaplastic oligo - astrocytoma ( pfs-6 44% versus pfs-6 38% in the present series , table  4 ) . the pfs-6 in group b and c ( all recurrent non - primary gbm s , with a contrast enhancing lesion on mri at the start of the ddtmz ) is higher than the pfs-6 found in the eortc study 26972 in recurrent oligodendroglioma , with or without combined 1p/19q loss after first line chemotherapy ( table  4 : pfs-6 3862% vs. 29% ) , although the pfs-12 is comparable ( table  4 : pfs-12 1315% vs. 11% ) . data on second line tmz in recurrent oligodendroglial tumors with combined 1p/19q loss are scarce , kouwenhoven et al . reported only one responder in nine patients treated after prior procarbazine , lomustine , and vincristine chemotherapy , but pfs-6 was not reported . almost none of the patients with a primary gbm or who grade 2 or 3 glioma without combined 1p/19q loss ( group a and b ) with a chemotherapy free interval of 3  months or less before the start of the ddtmz had a good outcome ( pfs-6 8% vs. 43% ; fisher exact test 0.033 ) . similar to the results of perry et al .   on metronomic tmz , ddtmz is not effective in patients with progressive disease within 3  months of previous chemotherapy . the patients with a dedifferentiated glioma with combined 1p/19q loss were left out of this analysis , because these patients have a completely different prognosis and response to chemotherapy and only two patients in this group had progressive disease within the 3  months before the start of the ddtmz . the single patient relapsing during standard tmz and responding to ddtmz had a progression free survival of 48  months up till now , suggesting he did nt have real tumor progression at the time of ddtmz . probably the enhancement on mri in this patient was caused by radionecrosis 45  months after rt . since all patients started ddtmz relatively long after ( chemo-)irradiation ( median time between start last rt and start ddtmz 24  months , range 5197 ; table  3 ) , it is unlikely that pseudoprogression played a role in this study . five patients were switched to the standard day 15 every 4  weeks tmz because of fatigue . after switch their fatigue improved . two patients developed pcp infections before routine monitoring of cd4 + counts , none of the monitored patients ( who received pcp prophylaxis with cotrimoxazol in case cd4 + counts decreased below 0.2 * 10/l ) developed a pcp infection . data from available phase 2 trials investigating ddtmz in gliomas indicate a high incidence of lymphopenia , especially in patient treated with the 3  weeks on/1  week off regimen [ 12 , 14 , 16 , 17 , 27 ] . in melanoma patients treated with daily tmz for 6  weeks out of every 8-week cycle , a high incidence of lymphopenia and an increased risk of opportunistic infections were reported . clearly , patients who receive ddtmz are at risk to develop pneumocystis carinii pneumonia , and prophylaxis is indicated in patients who develop lymphopenia or low cd4 + counts . although this study has a limited number of patients and is retrospective , it however seems from these results that ddtmz is an effective treatment for patients with a recurrence of gbm or otherwise heavily pre - treated gliomas , albeit with an increase in toxicity . whether it is more effective than the standard 5 of 28-day regimen remains unclear . although administration of ddtmz regimens causes more pronounced depletion of mgmt in peripheral blood mononuclear cells , the effects of ddtmz on mgmt activity in brain tumor tissue and its impact on clinical outcome remain unclear . a study from the united kingdom , comparing standard day 15 every 4  weeks tmz with a ddtmz schedule , ( given in a 3  weeks on/1  week off schedule ) failed to show any benefit of ddtmz in high - grade glioma recurrent after rt only in comparison to the standard day 15 every 4  weeks schedule . of note , although these patients were chemotherapy nave , one may assume that two - thirds of patients would have an unmethylated mgmt promoter . thus , if ddtmz would have been effective in overcoming that resistance , one would expect at least some trend toward a more favorable outcome in ddtmz treated patients . the recently reported rtog 0525 trial on newly diagnosed gbm also failed to produce superior outcome of ddtmz in newly diagnosed gbm ( and regardless of the mgmt promoter status ) .
alternative temozolomide regimens have been proposed to overcome o6-methylguanine - dna methyltransferase mediated resistance . 
 we investigated the efficacy and tolerability of 1  week on/1  week off temozolomide ( ddtmz ) regimen in a cohort of patients treated with ddtmz between 2005 and 2011 for the progression of a glioblastoma during or after chemo - radiation with temozolomide or a recurrence of another type of glioma after radiotherapy and at least one line of chemotherapy . 
 patients received ddtmz at 100150  mg / m2/d ( days 17 and 1521 in cycles of 28-days ) . 
 all patients had a contrast enhancing lesion on mri and the response was assessed by mri using the rano criteria ; complete and partial responses were considered objective responses . 
 fifty - three patients were included . 
 the median number of cycles of ddtmz was 4 ( range 112 ) . 
 eight patients discontinued chemotherapy because of toxicity . 
 two of 24 patients with a progressive glioblastoma had an objective response ; progression free survival at 6  months ( pfs-6 ) in glioblastoma was 29% . 
 three of the 16 patients with a recurrent who grade 2 or 3 astrocytoma or oligodendroglioma or oligo - astrocytoma without combined 1p and 19q loss had an objective response and pfs-6 in these patients was 38% . 
 four out of the 12 evaluable patients with a recurrent who grade 2 or 3 oligodendroglioma or oligo - astrocytoma with combined 1p and 19q loss had an objective response ; pfs-6 in these patients was 62% . 
 this study indicates that ddtmz is safe and effective in recurrent glioma , despite previous temozolomide and/or nitrosourea chemotherapy . 
 our data do not suggest superior efficacy of this schedule as compared to the standard day 15 every 4  weeks schedule .