High prevalence of human cytomegalovirus in brain metastases of patients with primary breast and colorectal cancers

Abstract

Background: Brain metastases (BMs) develop by largely unknown mechanisms and cause major morbidity and mortality in patients with solid tumors. Human cytomegalovirus (HCMV) is frequently detected in tumor tissue from patients with different cancers. Here, we aimed to determine the prevalence and potential prognostic role of HCMV in BMs.

Methods: We obtained archived samples of BMs from 41 patients with breast cancer and 37 with colorectal cancer and paired primary tumor tissues from 13 and 12 patients in each respective group. In addition, primary breast cancer tissues from 15 patients were included. HCMV proteins were detected with an immunohistochemical technique and Western blot. HCMV nucleic acids were detected with TaqMan polymerase chain reaction (PCR) assay.

Results: HCMV proteins were abundantly expressed in 99% of BM specimens, and in 12 of 13 (92%) paired primary breast cancer specimens. All 12 paired colon cancer samples were positive for HCMV proteins. Protein staining was mainly confined to neoplastic cells. Western blot analysis detected an HCMV-IE reactive protein in 53% of breast cancer specimens, and PCR detected the presence of HCMV DNA and transcripts in 92% and 80% of samples, respectively. Patients with high-level expression of HCMV-IE proteins in their tumors had a shorter time to tumor progression and shorter overall survival.

Conclusions: The prevalence of HCMV proteins and nucleic acids is very high in primary and metastatic tumors and may drive the development of metastatic brain tumors; therefore, this virus may represent a potential therapeutic target in metastatic cancer.

Figure 1

Summarizing results for all IHC staining on brain tumor tissues. Results from IHC staining from all brain tumor specimens including both IE and LA HCMV proteins were plotted in A and B, respectively.

Figure 2

IHC analysis of BMs from breast and primary breast cancers. HCMV proteins were detected in tissue sections of BMs (A–D) and in primary breast cancer tissues (G, J). HCMV-IE expression is confined to tumor cells in brain tumor specimens (A and B and G and H). Serial sections of the same tumor show immunoreactivity to HCMV-LA protein in the same tumor area (C and D and I and J). Cytokeratin was used as an epithelial marker and positive control for tumor cells (E) and β-catenin served as a staining control (K–L). Primary antibody was omitted as a negative control (F). Scale bars: (A, C, E, F, G, I, and K) 300 μm and (B, D, H, J, and L) 100 μm. Results of IHC staining for primary breast cancer specimens and BMs were plotted in M and N, respectively. HCMV-IE grade of primary tumor correlates with time to BM (O) and survival after primary tumor diagnosis (P). HCMV grade of BMs from breast cancers correlates with survival from diagnosis of BM to death (Q).

Figure 3

IHC analysis of BMs from colon cancer and primary colon cancer. HCMV-IE expression is confined to tumor cells in BMs specimens (A and B). Serial sections show immunoreactivity to HCMV-LA protein in the same tumor areas (for BMs: C-D and for primary colon cancer tissues: I-J). Cytokeratin was used as an epithelial marker and positive control (E) and β-catenin served as a staining control (K). Primary antibody was omitted as a negative control (F and L). (A, C, E, F, G, I, K and L) 300 μm; (B, D, H and J) 100 μm. HCMV-IE graded as low, < 50% positive cells and high, ≥ 50% positive cells. Results of IHC staining for primary breast cancer specimens and BMs were plotted in M and N, respectively. Time to BM (O) as well as survival after primary tumor diagnosis (P) and diagnosis of the BM (Q) were correlated with HCMV-IE infection grade.

Figure 4

Correlation of survival time with HCMV-IE grade. (A) Patients with low-grade HCMV-IE infection in BM samples have improved survival time from diagnosis of BM to death. Patients with low-grade HCMV-IE infection in primary colon and breast cancers have significantly longer time to BM (B) and survival time from diagnosis of the primary tumor (C).

Figure S3

IHC staining of HCMV-infected lung tissue section as a positive control. As a positive control for IHC staining, HCMV-infected lung tissue from an immunocompromised patient was stained for HCMV-IE (A and B). Scale bars: (A) 300 μm and (B) 100 μm.