The challenges of defining sample adequacy in an era of HPV based cervical screening

BACKGROUND

The implementation of Human Papillomavirus based cervical screening continues apace on a global scale. Understanding the basis and burden of inadequate or invalid samples is important to ensure confidence in high quality laboratory results and inform the development of new technologies. Here we present population based data from Scotland and Denmark which detail the extent of invalid samples for HPV detection in both clinician-taken and self-taken samples. As a comparator we report on the rate of inadequate cytology preparations in both countries.

METHODS

The proportion of samples with an invalid HPV test result was calculated by retrospective analysis of routine laboratory data associated with cervical screening programmes in the two countries. Two assays were in use for the programmes at the time (the Abbott RealTime High Risk HPV assay and the BD Onclarity); both have internal endogenous controls for human genes. In addition, acellular cytology samples were reported through a prospective audit (Scotland) and National quality reporting (Denmark).

RESULTS

In total, 89,418 clinician samples and 14,677 self-taken samples were assessed. We observed low rates of invalid HPV tests in clinician taken samples (0.05-0.10 %), irrespective of sample collection media (ThinPrep or SurePath), HPV test system/endogenous control type or clinical indication for testing (primary screening, triage or test of cure). For self-taken samples, the number of invalid samples was 0.18 %. Complete absence of sample material (acellular) in clinician taken samples were observed at a level of 1 in approximately 16.5 thousand.

CONCLUSIONS

Clinician and self-taken samples appear robust specimens for HPV testing and acellular samples are very rare. Efforts to develop endogenous controls for HPV assays that provide greater insight into true sample adequacy for cervical disease detection, beyond measuring the presence of human cells, will be welcome.

Methylation markers FAM19A4 and miR124-2 as triage strategy for primary human papillomavirus screen positive women: A large European multicenter study

In human papillomavirus (HPV) cervical cancer screening, cytology is used as triage to counter the low specificity of HPV testing. VALID-SCREEN is a EU-multicenter, retrospective study conducted to evaluate the clinical performance of the FAM19A4/miR124-2 methylation-based molecular triage test as a substitute or addition to cytology as reflex testing of HPV screen positive women. FAM19A4/miR124-2 methylation test (QIAsure Methylation Test) was evaluated in 2384 HPV-positive cervical screening samples, from women 29-76 years of age, derived from four EU countries. Specimens were collected in ThinPrep or SurePath media, HPV-status, concurrent cytology, and histology diagnosis were provided by the parent institutes. The control population consisted of women with no evidence of disease within 2 years of follow-up. A total of 899 histologies were retrieved; 527 showed no disease, 124 CIN2 (5.2%), 228 CIN3 (9.6%) and 20 cervical cancers (0.8%); 19 of 20 screen-detected cervical cancers were found methylation-positive (sensitivity 95%). Overall specificity of FAM19A4/miR124-2 methylation test was 78.3% (n = 2013; 95%CI: 76-80). The negative predictive value of hrHPV positive, methylation-negative outcomes were 99.9% for cervical cancer (N = 1694; 95%CI: 99.6-99.99), 96.9% for ≥CIN3 (95%CI: 96-98), and 93.0% for ≥CIN2 (95%CI: 92-94). Overall sensitivity for CIN3 using FAM19A4/miR124-2 methylation test was 77% (n = 228; 95%CI: 71-82). CIN3 sensitivity was uniform between centers independent of sample collection medias, DNA extraction methods and HPV screening tests. Being objectively reported compared to the subjectivity of cytology, equally performing across settings and screening methods, the FAM19A4/miR124-2 methylation constitute an alternative/supplement to cytology as triage method to be investigated in real-life pilot implementation.

Referral population studies underestimate differences between human papillomavirus assays in primary cervical screening

OBJECTIVE

We studied how representative cytologically abnormal women ("referral populations") are with respect to uncovering differences between human papillomavirus (HPV) assays in the primary screening where most women are cytologically normal.

METHODS

A total of 4997 women were tested with SurePath® cytology, and Hybrid Capture 2 (HC2), cobas, CLART and APTIMA HPV assays. Women with positive test results were offered a follow-up. For all detected HPV infections and HPV-positive high-grade cervical intraepithelial neoplasia (≥CIN2), we studied the distributions of assay-specific signal strengths in the baseline samples as documented by the assays' automatically generated reports. We calculated the likelihood of test result discordance as the proportion of HPV-positive samples that were not confirmed by all four assays.

RESULTS

Median signal strengths for HPV infections were weaker in normal than abnormal cytology (P<.001, adjusted for women's age, multiple infections and the reason for taking the sample). For HC2, they were RLU/CO 11.0 (interquartile range, IQR: 3.3-52.8) vs 124.2 (IQR: 22.8-506.9), respectively; for cobas, Ct 33.5 (IQR: 29.6-37.5) vs 26.9 (IQR: 23.7-31.3), respectively; for APTIMA, S/CO 10.2 (IQR: 5.8-11.3) vs 11.1 (IQR: 9.4-15.5), respectively. Similar patterns were observed for HPV-positive ≥CIN2. The four HPV assays more frequently returned discordant test results in normal than in abnormal cytology. Relative frequency of discordance in detecting HPV infections was 0.39 (95% confidence interval: 0.33-0.48) for abnormal vs normal cytology.

CONCLUSIONS

These data suggest that referral population studies, by not including sufficient numbers of cytology normal women, underestimate the differences between HPV assays that would become apparent in primary screening.

Human Papillomavirus Assays and Cytology in Primary Cervical Screening of Women Aged 30 Years and Above

In women aged ≥ 30 years, Human Papillomavirus testing will replace cytology for primary cervical screening. We compared Hybrid Capture 2 (HC2), cobas, CLART, and APTIMA HPV assays with cytology on 2869 SurePath samples from women undergoing routine screening at 30-65 years in Copenhagen, Denmark. Women with cytological abnormalities were managed according to routine recommendations, with 92% completeness. Those with cytology-normal/HPV-positive samples (on any of the four assays) were invited for repeated cytology and HPV testing in 1.5 year, and 58% had additional testing. HPV testing detected more ≥ CIN3 than cytology (HC2: 35, cobas, CLART: 37, APTIMA: 34, cytology: 31), although statistically the differences were not significant. Cobas and CLART detected significantly more ≥ CIN2 than cytology (cobas, CLART: 49, cytology: 39). The proportion of women with false-positive test results (positive test results without ≥ CIN3) varied between 3.3% with cytology and 14.9% with cobas. All HPV assays led to significantly more false-positive tests, whereas compared to HC2 cobas and CLART were associated with a significantly higher and APTIMA with a significantly lower proportion. Detection of CIN1 was particularly increased for the three DNA assays. With APTIMA combined with cytological triage, about 20% more women were referred for colposcopy than with cytology screening. With the three DNA assays, the increase was ≥ 50%. The number of women with repeated testing was twice as high with APTIMA and almost five times as high with cobas compared to cytology. To our knowledge, Horizon was the only study set in routine practice that compared more than two HPV assays in the same women while also ascertaining the histological status of women with normal cytology/HPV-positive test results. HPV-based screening of Danish women aged 30-65 detected more high-grade CIN but decreased the screening specificity, and increased the demand for additional testing.

Gene expression profiling of murine T-cell lymphoblastic lymphoma identifies deregulation of S-phase initiating genes

In a search for genes and pathways implicated in T-cell lymphoblastic lymphoma (T-LBL) development, we used a murine lymphoma model, where mice of the NMRI-inbred strain were inoculated with murine leukemia virus mutants. The resulting tumors were analyzed by integration analysis and global gene expression profiling to determine the effect of the retroviral integrations on the nearby genes, and the deregulated pathways in the tumors. Gene expression profiling identified increased expression of genes involved in the minichromosome maintenance and origin of recognition pathway as well as downregulation in negative regulators of G1/S transition, indicating increased S-phase initiation in murine T-LBLs.

Coupling of receptor interference and a host-dependent post-binding entry deficiency in a gammaretroviral envelope protein

Background

SL3-2 is a unique polytropic murine gammaretroviral isolate that is only able to infect murine cells. We have previously shown that two mutations R212G and T213I located on the surface of the receptor binding domain in a region designated the VR3 loop can alter the species tropism of this envelope protein. This location suggests that the VR3 loop composition has an influence on receptor interaction and thereby affects binding as well as superinfection resistance. In order to investigate this further, we have studied the binding and interference patterns of the SL3-2 envelope and its mutants.

Results

We find unexpectedly that wild type SL3-2 envelope binds equally well to both permissive and non-permissive cells, indicating a post binding defect when interacting with the human Xpr1. Using replication competent viruses containing envelopes from SL3-2 or its mutants we find that the same amino acid mutations can dramatically alter the interference profile of this polytropic ENV, suggesting that the same amino acid changes that cause the post binding defect also influence interaction with the receptor.

Conclusions

The envelope protein of SL3-2 MLV shows an entry defect on non-murine cells. This is coupled to a dramatically reduced ability to interfere with entry of other polytropic viruses. Two point mutations in the VR3 loop of the receptor binding domain of this envelope result both in a much increased interference ability and in removing the post-binding defect on non-murine cells, suggesting that both of these phenotypes are a consequence of insufficient interaction between the envelope and the receptor