Retrospective analysis of HPV 16/18-related disease burden using archival clinical samples.

PURPOSE: Estimation of HPV-related disease burden lies at the core of effective disease management. HPV testing is heavily reliant on its retrospective detection in archival clinical cancer samples, especially in parts of the world where HPV screening is not routinely practiced. During the last decade, valuable insights were gained through regional reports based on occasional screening of cervical smears or biopsy sections for the presence of high-risk HPV. HPV 16 and 18 were found to be predominant high-risk HPV subtypes with some regional differences and incidences of co-infections, detected mostly through PCR-based methods. In cases of multiple infections, the presence of viral DNA may not signify its etiologic involvement. The current study, therefore, combines PCR-based detection method with the immunohistochemical (IHC) detection of early viral protein E6 expression, in order to obtain a reliable read out for the disease causing viral subtype, especially in cases of co-infections with oncogenic subtypes other than HPV 16 and 18. Immunohistochemistry (IHC) and PCR-based methods are routinely used laboratory techniques in local hospitals. The concordance between IHC and PCR-based analyses may be useful for determining effective method for the retrospective testing of HPV 16 and 18 disease-related burden.

METHODS: A total of 49 paraffin-embedded cervical cancer biopsy sections representing patients from the northwest region of the country were collected from the tertiary care hospital for this study. Genotyping for HPV 16 and 18 was carried out through PCR. The HPV 16/18 E6 protein expression was evaluated by IHC and was compared with the clinicopathological features of cervical cancer.

RESULTS: Molecular analysis of 33 (67 %), E6-expressing paraffin-embedded cervical cancer biopsy sections revealed the presence of HPV 16 (n = 23; 47 %), HPV 18 (n = 6; 12 %) and co-infection (n = 4; 8 %) in 49 tumors through PCR. Despite the PCR-based detection of viral DNA in 37 cervical cancer samples, IHC analysis of E6 expression revealed the etiological involvement of HPV 16/18 in 33 out of 37 cervical cancer samples. Overall, there was 85 % concordance in the results of the two techniques.

CONCLUSION: IHC analysis provides more conclusive evidence regarding the etiological involvement of the viral subtypes, especially in the presence of multiple infections. About two-thirds (67 %) of cervical cancer samples were found to be caused due to HPV 16/18. Latent occurrence of HPV 16 and 18 is suggested in less than 10 % cervical cancer samples which were found to harbor viral DNA without E6 expression. Furthermore, E6 expression was found to be significantly correlated with the tumor grade.