Prognosis of MGMT-Positive Gene in Patients with Brain Tumors of Grade III and Grade IV

Introduction

Glioblastoma multiforme (GBM) is the most aggressive type of brain cancers. Diagnosis is often delayed because initial signs and symptoms of glioblastoma are non-specific, including headaches, personality changes, nausea, and symptoms, similar to those of a stroke. Symptoms often worsen rapidly and may progress to unconsciousness. Genetic risk factors include neurofibromatosis and Li–Fraumeni syndrome. Previous radiation therapy is also a risk factor.1 The current WHO classification recognizes three variants of GBM including conventional glioblastoma, giant cell glioblastoma, and gliosarcoma.2 Standard of care for newly diagnosed GBM is surgery followed by radiation therapy with the addition of temozolomide.34

Tumor markers are gaining importance in the era of targeted therapy. O6-methylguanine DNA methyl transferase (MGMT) is crucial for genome stability. It repairs the naturally occurring mutagenic DNA lesion O6-methyl guanine back to guanine and prevents mismatch and errors during DNA replication and transcription.5 Epigenetic silencing of the MGMT gene by promoter methylation results in decreased MGMT protein expression, reduced DNA repair activity, and potential increased sensitivity to therapy. Epigenetic MGMT gene silencing by promoter methylation is associated with loss of MGMT expression and diminished DNA repair activity. This results in increased sensitivity to temozolomide and longer overall survival (OS).456

Methods and Materials

We conducted a single-institute retrospective study between 2018 and 2021.

All patients with WHO Grade III and IV brain tumors confirmed on histopathology were included in the study. All patients below 18 years of age and those with low-grade brain tumor were excluded.

Our department policy is to offer MRI brain with contrast and MGMT gene testing (done by RT-PCR) in all patients. The objective of surgical therapy is to do surgical excision wherever possible.

All patients were given adjuvant external beam radiotherapy (EBRT) along with concurrent temozolomide. Individual cast formation and CT simulation images, and transferring to the programming system via DAICOM, where gross tumor volume (GTV) and contouring according to the initial size of the tumor, i.e., the size of the tumor before surgery and clinical tumor value (CTV) margin of 1.5 cm and planned tumor volume (PTV) margin of 0.5 cm is as per the standard guidelines adopted by our department.7 PTV was planned to dose of 60 Gy in 30 fractions, 5 days a week with a coverage of 95%, and minimal allowed dose to organ at risk7 along with concurrent temozolomide (75 mg/m²) daily. Regular weekly follow-up schedule was for 6 weeks and routine hematological investigation was planned weekly.8

After completion of EBRT, the patients' schedule was adjuvant temozolomide for 12 monthly cycles. MRI brain with contrast was planned every 3rd, 6th, and 12th months of adjuvant cycle of temozolomide. Patients were advised anti-epileptics during entire treatment.9

Our objective was to evaluate whether MGMT gene positivity is associated with better survival in patients diagnosed with GBM treated in a single institution.

Results

A total of 80 MGMT-positive patient were included in the analysis of this retrospective study. Of them, 56 were males and 24 were females. Age ranging from 32 to 64 years of age (median 49 years). Out of 80 patients, 75 underwent subtotal excision and 5 underwent total excision of tumor.

Out of 75 patients who underwent subtotal excision, 27 were of WHO Grade III and 48 were of WHO Grade IV. Also, out of 5 patients who underwent total excision, one patient was of WHO Grade III and four were of WHO Grade IV.

Out of 80 patients, isocitrate dehydrogenase 2 (IDH2) was lost in all patients. ATRX was lost in 52/80 patients, whereas it was present in 28 individuals.

The median PFS and OS in five patients in total excision in Grade III patient was 9.0 and 20 compared with Grade IV, where the median PFS and OS was 8.8 and 17.8 months. Out of 75 patients in the subtotal group, the median PFS and OS, respectively, in Grade III group was 9.1 and 19.3 and, WHO grade IV with median PFS of 8.8 and OS of 18.8. PFS and OS were measured from the time of surgery to disease progression or death, respectively (Table 1).

Discussion

Our data confirmed that MGMT gene positivity is associated with a favorable outcome after temozolomide chemotherapy in patients with newly diagnosed WHO Grade III and IV brain tumor. The methylation status of the MGMT promoter is therefore of prognostic value and predicts benefit from temozolomide chemotherapy.

In a meta-analysis of 30 studies with 2,986 patients across different countries, the frequency of MGMT promoter methylation was 44.27%. It showed that MGMT gene positivity was associated with better PFS and OS in patients with GBM, regardless of therapeutic intervention. Longer OS in GBM patients was also documented in patients treated with alkylating agents.1

When compared with the global literature, we found interesting geographical variations in MGMT gene methylation across different countries. The highest is of Switzerland (68.42%) and France (67.90%). The lowest incidence (31.58%) was reported from Czech Republic (Fig. 1).1011121314151617181920

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Fig. 1: MGMT positivity rate in brain tumor geographical map.

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Hegi et al also concluded that patients with glioblastoma containing a MGMT positivity benefited from temozolomide, conversely those who did not have a methylated MGMT promoter failed to benefit from temozolomide. They concluded that the median overall survival among patients with methylation was 18.2 months (95% confidence interval, 15.5 to 22.0), as compared with 12.2 months (95% confidence interval, 11.4 to 13.5) among those without methylation.6

Kim et al in study of 93 patients determined that the median OS was 29 months for the methylated group (MGMT positive) and 20 months for the unmethylated group (MGMT negative). In 35 patients with methylated MGMT genes, the 2-year and 5-year OS rates were 54% and 31%, respectively.11

Compared with above studies, we found the PFS and OS in grade IV tumor was 8.8 months and 17.8 months in the total excision group, while in the subtotal group, it was 8.8 months and 18.8 months. There was no difference because of small numbers.

Interestingly, CATNON, EORTC study 26053–22054 concluded that adjuvant temozolomide chemotherapy, was associated with a survival benefit in patients with 1p/19q non–co-deleted anaplastic glioma. However, they did not give concurrent temozolomide.21

Diagnostic MGMT testing requires sufficient and optimally preserved tumor tissue. The best results with methylation-specific PCR are obtained when cryopreserved tumor specimens are used. Fixation is known to result in the deterioration of tumor DNA, leading to false negativity. Other methods, such as immunohistochemistry, may not be reliable because MGMT expression is prone to induction by glucocorticoids, ionizing radiations, and genotoxic agents when the MGMT promoter is not methylated.2223

Limitations of our study include being single-institute study, having a small number of patients and a few patients eligible for complete resection. We have also not studied other genetic alterations that could influence outcome.

Conclusion

MGMT gene positivity is a prognostic factor in Grade III and IV brain tumors. Determination of MGMT gene positivity status by methylation-specific PCR may allow the selection of patients most likely to benefit from temozolomide treatment. Such patients are likely to have a longer PFS as well as overall survival.