Human cytomegalovirus infection levels in glioblastoma multiforme are of prognostic value for survival

Abstract

Background

Patients with glioblastoma multiforme (GBM) generally live 12–15 months after diagnosis, despite maximal surgical resection, adjuvant radiotherapy, and chemotherapy. HCMV has been detected in 90–100% of GBMs. We recently found that low grade HCMV infection in GBM tumours was highly associated with survival over 18 months (case–control study). Here, we sought to determine whether low-grade HCMV infection in GBMs is associated with prolonged survival in a consecutive patient cohort, analysed retrospectively.

Study design

Tumour samples from 75 consecutive GBM patients treated surgically at Karolinska University Hospital in 2004–2005 were examined by immunohistochemistry (IHC) and in situ hybridization for HCMV proteins and DNA, respectively. Tumours were graded 1–4, depending on the percentage of positive cells by IHC. Low-grade HCMV was defined as grade 1 (<25% of HCMV infected tumour cells). Time to tumour progression (TTP) and survival data were analysed with Cox regression and Kaplan–Meier models.

Results

HCMV infection was detected in 74 of 75 tumours (99%). In patients with low-grade HCMV infection, median survival was 20 months longer than in patients with high-grade infections (P = 0.036, HR: 2.2), and TTP was 8 months longer (P = 0.1, HR: 1.8). Two-year survival was much higher in patients with low-grade HCMV infection (63.6% vs. 17.2%, P = 0.003).

Conclusion

The longer survival in patients whose tumours had low-grade HCMV infection suggests that the level of HCMV infection in GBMs has a prognostic value and that HCMV may contribute to the pathogenesis of GBM.

Introduction

Glioblastoma multiforme (GBM) is the most malignant primary tumour of the central nervous system.¹ The median survival after diagnosis is 12–15 months.² Although 90–100% of GBMs are infected with human cytomegalovirus (HCMV),3, 4, 5 it is unclear whether this virus contributes to tumour development or progression.

HCMV is a herpesvirus carried by 70–100% of the world's population. In healthy persons, HCMV infection is generally asymptomatic; however, the virus remains latent in the bone marrow and peripheral blood and can be reactivated by inflammation.6, 7, 8 Emerging evidence demonstrate that HCMV can be detected in certain malignant tumours, such as GBM,3, 4, 5 colon cancer,⁹ breast cancer¹⁰ and prostatic carcinoma,¹¹ mucoepidermoid carcinoma of salivary glands¹² and rhabdomyosarcomas.¹³ Using immunohistochemistry, flow cytometry, PCR and in situ hybridization techniques, we and others have detected HCMV in tumour tissue specimens.¹⁴ However, some investigators have not confirmed the finding of HCMV in tumours.15, 16, 17 In our own experience, we can readily detect the virus in frozen tumour specimens by indirect immunofluorescence or in paraffin embedded tumour tissue specimens using the high sensitive immunostaining protocols, which include optimal tissue fixation, antigen retrieval, use of appropriate antibodies for paraffin embedded tissues and blocking of nonspecific binding.3, 4, 5, 9, 10, 11, 12, 14 However, we do not detect the virus in tumours using regular immunohistochemistry protocols. Therefore, different detection methods used by different investigators, in particular the staining procedures, may be the main reasons why some studies have failed to detect HCMV in tumour tissues.15, 16, 17

Although one HCMV protein, US28, has an oncogenic potential,¹⁸ this virus is not considered to be oncogenic. Rather, it may be an oncomodulator that contributes to cancer development by modifying tumour cell biology.¹⁹ In such scenario, the level of HCMV infection in the tumour may affect disease progression and the prognosis of patients with HCMV positive tumours. In support of this hypothesis, we recently observed that a low-grade HCMV infection was strongly associated with long-term survival in GBM patients (P = 0.0006)⁵ in a case–control study. Here, we aimed to determine if low-grade HCMV infection in a consecutive cohort of GBM patients was associated with prolonged overall survival. We also defined the prevalence of Epstein–Barr virus (EBV) and herpesvirus 6 (HHV-6) as controls for viral persistence.