Patricia F. Fitzpatrick Dimond Ph.D. Technical Editor of Clinical OMICs President of BioInsight Communications
Can Screening for Cancer-Causing Viruses Predict Progression and Treatment Outcome?
Although many viruses cause various tumors in animals, to date, only seven have associated with human cancers. Nucleic acid-based screens will likely play a greater role in screening for cancers with viral origins—perhaps even replacing Pap smears for first-line cervical cancer screening and for assessment of treatment responses—and may be increasingly used to detect diseases such as non-Hodgkin lymphomas and nasopharyngeal carcinoma.
Known human oncogenic viruses (AKA oncoviruses)—which can include both DNA and RNA viruses—are hepatitis B virus (HBV), hepatitis C virus (HCV), human papillomavirus (HPV), Epstein-Barr virus (EBV), human herpes virus 8 (HHV8), Merkel cell polyomavirus (MCPyV), and HTLV-1.
Both DNA and RNA oncogenic viruses can induce cancer through a variety of mechanisms. Investigators say that a “unifying theme” among virally caused cancers is that they develop in a minority of infected individuals and only after chronic infection of many years duration. Recently, several viral nucleic acid detection tests have been developed for the identification of progressive virally caused cancers and to assess and follow treatment responses.
The viruses associated with the greatest number of cancer cases are the HPVs that cause cervical cancer and several other epithelial malignancies, the DNA-based HBVs, and RNA-based HCV. The most common risk factor for liver cancer worldwide is chronic infection with HBV or HCV.
HPVs infect the epithelial surface of the skin and mucous membranes in humans and other animal species. HPV oncogenic strains of HPV associated with human cancers include cervical and anal cancers and squamous cell carcinoma of the head and neck region, specifically of the oropharynx (causing about 40–60% of oropharyngeal carcinomas), as well as 70% of cervical cancers (CCs). Two viral oncogenes—E6 and E7, invariably expressed in HPV-positive cancer cells—inactivate two major tumor suppressors, p53 and RB.
But not all not all infections with high-risk HPVs persist or progress to cervical cancer, suggesting that, although necessary, HPV infection alone is not sufficient to induce this disease. Other factors, environmental or host-related, are likely also involved.
The three licensed HPV prophylactic vaccines, Merck’s Gardasil (human papillomavirus 9-valent vaccine, recombinant) and Gardasil 9 (human papillomavirus 9-valent vaccine, recombinant), as well as GlaxoSmithKline’s Cervarix (human papillomavirus vaccine)—have very high and proven efficacy against new infection with HPV16 and HPV18 and the resulting CIN2 and CIN3 lesions. They also confer partial protection against HPV31 (which is closely related to HPV16) and HPV45 (which is closely related to HPV18). These vaccines provide strong protection against new HPV infections, but are ineffective at treating established HPV infections or disease caused by HPV. Within the next few years, augmented prophylactic vaccines that prevent virtually all carcinogenic types of HPV infection may be licensed.
In the context of concerns surrounding mandating vaccinations for young girls and lobbying by pharma companies, Diane Harper, MD, a professor at the University of Missouri-Kansas City School of Medicine, believes the vaccine is being oversold, despite having directly participated in studies that got the two currently anti-HPV vaccines approved by FDA.
“Ninety-five percent of women who are infected with HPV never, ever get cervical cancer,” she says. “It seemed very odd to be mandating something for which 95% of infections never amount to anything.”
But she noted in Expert Review Vaccines while most HPV infections never progress to cancer, the small fraction of HPV infections that do become cervical cancer cause over 250,000 deaths annually worldwide.
And to investigators focused on HPV research in cervical cancer, the challenge of cervical cancer screening is to detect the lesions that have a high risk of progression. HPV testing can identify women who remain at high risk of recurrence following surgical of their cancers. Negative HPV tests after excision predicts they say a high probability of cure.
Eileen M. Burd, Ph.D., professor at Emory University’s Pathology and Laboratory Medicine department, told GEN that molecular tests “will become the primary screen.” She notes, “Vaccines will suppress the cervical cancers caused by the specific subtypes included in the vaccine and cancers that do occur will be caused by other high-risk HPV types.” And, she notes, due to the nature of HPV cancers, “serial testing will give a better picture of what’s going on.”
Beginning December 1, 2017 Australian women from the age of 25 (instead of 18), will be required to have a five-yearly HPV test, replacing the two-yearly pap test.
“We found that the HPV test was substantially more effective at picking up high-grade abnormalities compared to the pap test,” said Karen Canfell, M.D., professor and director of research at Cancer Council New South Wales, said in a press release.
But to aid in monitoring the possibility that high-risk genotypes not covered by the vaccine can predominate in cervical cancer in the future, there is a need for high-throughput broad-spectrum genotype assays, investigators say.
On April 24, 2014, the Food and Drug Administration (FDA) approved the use of one HPV DNA test, (cobas HPV test, Roche Molecular Systems, Inc.) as a first-line primary screening test for use alone for women age 25 and older. This tests for HPV types 16 and 18 and gives pooled results for 12 additional high-risk HPV types. The tests utilize amplification of target DNA by the polymerase chain reaction (PCR) and nucleic acid hybridization for the detection of 14 high-risk HPV (hrHPV) types in a single analysis.
Epstein-Barr Virus (EBV)
Epstein-Barr Virus (EBV) is associated with a range of malignancies, including post-transplant lymphoproliferative disorder (PTLD), Hodgkin and non-Hodgkin lymphomas, nasopharyngeal carcinoma, gastric carcinoma, leiomyosarcoma nasopharyngeal carcinoma, Burkitt’s lymphoma, and Kaposi’s sarcoma. Increasingly, investigators have determined that cell free (cf) EBV DNA can serve as a marker for response to treatment and tumor progression in some these cancers.
Chen et al. investigated whether EBV DNA in plasma samples would be useful to screen for early nasopharyngeal carcinoma in asymptomatic persons.
Participants with initially positive results were retested approximately 4 weeks later, and those with persistently positive EBV DNA in plasma underwent nasal endoscopic examination and magnetic resonance imaging (MRI). A significantly higher proportion of participants with nasopharyngeal carcinoma identified by screening had stage I or II disease than in a historical cohort and had superior three-year progression-free survival.
Analysis of EBV DNA in plasma samples proved useful, the investigators concluded, in screening for early asymptomatic nasopharyngeal carcinoma. Nasopharyngeal carcinoma was detected significantly earlier, and outcomes were better in participants who were identified by screening than in those in a historical cohort.
Kanakry et al. sought to determine whether plasma EBV-DNA could serve as a surrogate for by Epstein-Barr encoding region in situ hybridization (EBER-ISH) and to explore its prognostic utility in Hodgkin’s lymphoma. Specimens from the Cancer Cooperative Intergroup Trial E2496 were used to compare pretreatment plasma EBV-DNA quantification with EBV tumor status by EBER-ISH.
Patients with pretreatment EBV (+) plasma had worse failure-free survival (FFS) compared with those with pretreatment EBV (-) plasma. By contrast, no difference in FFS was observed when patients were stratified by EBER-ISH. Pretreatment plasma EBV positivity proved an independent predictor of treatment failure on multivariate analyses. At month 6, plasma EBV (+) had inferior FFS compared with plasma EBV (-) patients.
These results confirm that plasma EBV-DNA is highly concordant with EBER-ISH in Hodgkin lymphoma and suggest that its measurement may have prognostic utility, both at baseline and after drug therapy.
Overall, the investigators said, their results indicated that although circulating nonspecific DNA loads were elevated at presentation, levels were not indicative of lymphoma burden once therapy had commenced. In contrast, circulating c-f EBV-DNA (but not cell-associated EBV-DNA) did reflect therapeutic response in EBV-associated lymphomas.
As detection and measurement of oncogenic virus cf-nucleic acids continues to move toward adoption as a first-line screen in some cancers, newly identified associations between viruses and specific cancers will continue to unfold.
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