Glioblastoma multiforme (GBM) has been a conundrum for all clinicians. The standard approach includes maximal safe resection, irradiation with concurrent temozolomide (TMZ), and 6 cycles of adjuvant TMZ.1 Addition of chemotherapy to radiotherapy can prolong survival among GBM patients, with a median increase in survival of 2.5 months.1 Since then, no further breakthrough treatment has emerged.

Of note, there is still insufficient evidence to support 6 cycles as the optimal adjuvant amount of TMZ for GBM. Only few studies have suggested that extended use of TMZ is safe and beneficial for prolonged survival.2 The main concern of extended use of TMZ is haematological toxicity. It is attributed to the depletion of O⁶-methylguanine-DNA methyltransferase (MGMT) protein activity in both GBM cells and haematopoietic stem cells.3 Nonetheless, compared with other alkylating agents, the low toxicity profile of TMZ has motivated clinicians to try its extended use after balancing the benefits and side-effects for each patient.4

Our institution offers the option for GBM patients with at least stable disease to step up to adjuvant cycles of TMZ. In this study, we report the experience of extended use of TMZ and its impact on newly diagnosed GBM patients.

We retrospectively reviewed the brain tumour registry of the Chinese University of Hong Kong Otto Wong Brain Tumour Centre, and identified patients with primary GBM during January 2010 to December 2013. Those patients who received surgical intervention and standard concomitant chemoradiotherapy after surgery (60-Gy irradiation with concomitant TMZ for 6 weeks, then followed by at least 6 cycles of adjuvant TMZ) were chosen as candidates for the study.

An experienced neuroradiologist was responsible for determining the extent of resection (EOR) by reading the postoperative day-1 magnetic resonance imaging (MRI) scans. A total resection indicated that the entire preoperative contrast-enhanced lesion seen on T1-weighted images was excised. If there was residual enhancement on T1-weighted images as well as T1-subtraction sequence, the case would be labelled as subtotal resection.

As a standard practice, a postoperative irradiation of 60 Gy was given to all patients within 4 weeks of surgery. Temozolomide was prescribed concurrently during radiotherapy at 75 mg/d/m² for 6 weeks, followed by 6 or more cycles of adjuvant TMZ at a dosage of 150-200 mg/d/m² for 5 consecutive days every 28 days. After completion of standard 6-cycle TMZ, all patients with at least stable disease were offered the chance of extended TMZ, regardless of individual prognostic factors. Whether or not they proceeded to extended TMZ was a decision made principally by patients and their relatives and also with neurosurgeons and clinical oncologists, on the basis of a detailed assessment of the patient’s clinical performance (neurological status and toxicity profile) and tumour response to TMZ. Anti-emetics were given during the 5 days. To achieve early detection of TMZ toxicity, haematological profile including complete blood picture with differential count, and liver and renal functions were assessed monthly on about day 21 to day 25. Toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE), version 4.0.5

All patients were followed up regularly with both clinical and radiological assessments of disease status. They were seen by a neuro-oncologist every 2 weeks after surgery, daily during irradiation, and monthly when being given adjuvant TMZ. For radiological assessment, patients were subjected to a scanning protocol with contrast-enhanced MRI of the brain at postoperative day 1, 2 weeks after completion of radiation, and every 3 months thereafter. These standardised protocols ensured that disease progression of all patients could be monitored in a timely manner. Disease progression was determined according to Macdonald’s criteria. In short, deteriorating neurological status, increasing tumour size, and appearance of new enhancement were suggestive of disease progression.6

Progression-free survival (PFS) was calculated from the date of surgical intervention to the date of progression. As the aim of this study was to compare the therapeutic effect of standard 6-cycle TMZ with that of more than 6 cycles of TMZ, only patients with neither neurological deterioration nor radiological signs suggesting progression for more than 28 days upon completion of the sixth cycle of adjuvant TMZ were eligible. The MGMT promoter status and EOR were regarded as categorical factors while age and cycles of adjuvant TMZ were assigned as the continuous variables for which correlation was chosen as the tool for analysis. t Test, U test, and correlation were chosen accordingly to examine the impact on PFS of each factor. For those factors with a P value of <0.05 in univariate analyses, a Cox regression hazard model was adopted to determine those strongly related to PFS. All statistical analyses were done using the SPSS (Windows version 22.0; IBM Corp, Armonk [NY], US).

This audit review was conducted in accordance with the principles outlined in the Declaration of Helsinki.

From January 2010 to December 2013, there were 14 patients who fulfilled the inclusion criteria. Their mean age at presentation was 52 (range, 25-71) years with a male preponderance: 10 male versus 4 female patients. Total resection was achieved in seven patients. For the remaining seven, six underwent subtotal resection and one could only have tumour biopsy. The MGMT promoter status was available in all cases and was methylated in 12 cases and unmethylated in the remaining two. After completion of standard concomitant chemoradiotherapy in all cases, extended adjuvant TMZ was initiated in seven cases (Table 1).

In total, 134 cycles of adjuvant TMZ were given, with 92 cycles given to the seven patients who proceeded to extended maintenance TMZ treatment. The median number of cycles given was 13 (range, 8-26) in the latter group. With regard to TMZ-related toxicity, two patients in the 6-cycle group had grade 1 haematological toxicity (thrombocytopaenia and neutropaenia) and one patient in the >6-cycle group developed mildly deranged alanine aminotransferase (ALT; grade 1, defined as “more than upper limit of normal and less than three times the upper limit of normal by CTCAE”5) during the fifth cycle of adjuvant TMZ that subsequently subsided.

Progression-free survival differed significantly between the two groups: 17.0 (95% confidence interval [CI], 14.4-19.6) months for 6-cycle versus 43.4 (95% CI, 17.8-69.0) months for the >6-cycle group (P=0.007, log-rank test; Fig).

Progression-free survival at 12 months was 85.7% for both groups, and that at 18 months declined to only 28.6% for the 6-cycle group compared with 71.4% for the >6-cycle group (Table 2; Fig).

Three out of seven patients in the >6-cycle group were still alive at their last follow-up. Their median overall survival was 48.4 (95% CI, 24.3-72.4) months. In the 6-cycle group, the median overall survival was 30.9 (95% CI, 22.4-39.4) months. No statistical significance was observed by the end of the study (P=0.07, log-rank).

All factors including age, gender, and MGMT status were well balanced, except for the EOR. Despite the higher proportion of patients with subtotal resection who elected to receive extended TMZ, EOR was not predictive of longer PFS (P=0.482, Mann-Whitney U test). When subgrouping the cohort with MGMT promoter status, there was no evidence to suggest that methylated MGMT promoter status favoured patients with better PFS (P=0.882, Mann-Whitney U test). Age was also not correlated with PFS (P=0.09, Pearson correlation). Cox regression hazard model suggested that increased cycles of TMZ were associated with prolonged PFS (P=0.016; hazard ratio=0.68 per cycle; 95% CI, 0.48-0.94) [Table 3].

Despite recent advances in its therapy, GBM is still an incurable disease, characterised by rapid and inevitable recurrence even with intensive treatment. Ample clinical research has been carried out with the intention of defeating the disease, but the prognosis of GBM remains dismal. Temozolomide is the first chemotherapeutic agent proven to be effective. The standard treatment after maximum safe resection has two components, irradiation with concomitant TMZ and adjuvant TMZ at a higher dosage for 6 cycles. Under this regimen, survival is favourably improved.1 Since then, no other encouraging milestones have been achieved.

Our audit review showed a significant correlation between the number of cycles of TMZ and PFS. One patient in the >6-cycle group showed a continuous yet prominent shrinkage of the non-operable GBM (bilateral corpus callosum) after initiation of the seventh cycle of TMZ and finally achieved complete response after 12 cycles. The patient had only mildly deranged ALT during the fifth cycle of adjuvant TMZ and this subsided on its own.

Temozolomide was well-tolerated by most patients. One of our previous studies also demonstrated its satisfying anti-tumoural activity as well as its safety profile among ethnic Chinese population.7 Extended usage of TMZ upon completion of standard 6-cycle adjuvant courses has become common practice in many institutions.4 8 9

A literature search revealed only a few reports with similar settings and conclusions. Three non-randomised retrospective studies with decent sample sizes demonstrated an indispensable impact of extended adjuvant TMZ. The reported PFS ranged from 13 to 24.6 months; the overall survival was also improved.2 8 10 One very recent pooled analysis of four randomised clinical trials, however, showed a slightly different result—PFS was the only outcome that increased with the cumulative prescription of TMZ.11 Blumenthal et al11 reported that treatment with extended maintenance TMZ was significantly associated with better PFS with a hazard ratio of 0.77 (6 cycles vs >6 cycles). To conclude, the positive impact of long-term use of TMZ on PFS is supported by much evidence. Its influence on overall survival, however, needs further clarification.

By sacrificing its only alkyl component to the TMZ-induced lethal depletion of alkyl products on tumoural DNA, MGMT serves as a suicidal DNA repair enzyme. Theoretically, this irreversible depletion of the MGMT protein could be exploited by increasing tumoural exposure to TMZ. The effect might be even more prominent when MGMT promoter is hypermethylated, although the impact of MGMT promoter methylation could not be demonstrated in the present study. Nonetheless this mechanism also accounts for myelosuppression, the main concern of long-term use of TMZ, since MGMT protein in normal cells can also be depleted by TMZ. It is more common in haematopoietic stem cells contributing to toxicity for patients using this alkylating agent.3 In a cohort that comprised 114 patients, 39 (34%) were observed to have CTCAE grade 3 haematological toxicity during administration of TMZ. The study included all patients who received 1 to 57 cycles of TMZ.8 The French SV3 Study also evaluated the effect of prolonged TMZ and suggested that 39.6% of cases developed haematological toxicity beyond the second cycle.10 Toxicity to a certain degree discourages both clinicians and patients from increasing the dosage of TMZ during adjuvant therapy, and for extending use of TMZ beyond 6 cycles. In the current study, only 21.4% (3/14) of our patients encountered mild side-effects. Neuro-oncologists, however, remain reluctant to persuade patients to receive long-term TMZ. It is generally accepted by clinicians that long-term use of alkylating agents is unwise since they are likely to be the eventual cause of myelosuppression and secondary cancers.

In our institute, all patients with at least stable disease for more than 28 days after completion of the sixth cycle of adjuvant TMZ will be offered the option of continuing TMZ beyond 6 cycles, after being given detailed information about possible future side-effects. Of note, TMZ is funded in Hong Kong only for the first six adjuvant cycles; patients need to pay thereafter, making the inherent socio-economic bias unavoidable.

This study had several limitations. The sample size was relatively small. The analyses presented may provide only limited and preliminary evidence. Moreover, due to the nature of this study, only patients with disease responsive to TMZ yet with no or mild TMZ-related toxicity were qualified for the study.

Extended treatment with TMZ is safe and effective in Chinese patients with disease that is responsive to it. Careful assessment and consideration of continuing adjuvant TMZ is feasible for this group of patients.

All authors have disclosed no conflicts of interest.

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