HPV infection, especially high-risk HPV infection, is closely related to the occurrence of cervical precancerous lesions and cervical cancer and about 99.7% of cervical cancer patients have HPV infection. The most common type of HPV infection is HPV16 infection[8–10]. At present, the detection methods of HPV are mostly at the level of RNA or DNA, and there are few detection methods of oncoprotein. Studies have confirmed that after cervical epithelial cells are infected with HPV, the expression of the E6, E7 oncoprotein co-action lead to the occurrence of cervical cancer [11, 12], and the advanced stage of cervical cancer is mainly associated with E6 oncoprotein, early cancer stage is closely related to the E7 oncoprotein. Therefore, the detection of HPV16 E7 oncoprotein in the cervix has important clinical value for the early detection and diagnosis of cervical precancerous lesions and cervical cancer.
At present, the methods used to detect HPV E6/E7 oncoprotein include: semi-quantitative detection of HPV E6/E7 oncoprotein in pathological tissues using immunohistochemistry, qualitative detection of HPV E6/E7 oncoprotein in cervical exfoliated cells using enzyme immunochromatography, and qualitative detection of HPV E6/E7 oncoprotein in cervical exfoliated cells using immunocytochemistry [14–16]. The above-mentioned methods have their own inadequacies. The enzymatic chemiluminescence method used in this study can semi-quantitatively detect the expression level of HPV16 E7 oncoprotein in exfoliated cells of the cervix, which is easy to obtain, and the detection method is simple and rapid. It has a great potential in the clinical application.
In the first part of the study, we performed a correlation analysis of the expression levels of HPV16 E7 oncoprotein in 100 cases of different degrees of cervical lesions. The results showed that the expression of HPV16 E7 oncoprotein was positively correlated with the degree of cervical lesions, which is consistent with past research results[15, 16]. It was shown that HPV16 E7 oncoprotein expression increased with the severity of cervical lesions, suggesting that HPV16 E7 oncoprotein detection can be used as a screening for cervical precancerous lesions and cervical cancer. A large number of clinical studies have shown that about 60% of LSIL patients will naturally subside, only need close observations of the follow-up patients. About 20% of HSIL will continue to develop, and 5% will develop to invasive cervical cancer. Therefore, all patients with HSIL and higher degree of cervical lesions need to be treated . So we divided the first part of the 100 women into two groups: (1) normal cervix and LSIL group as the control group; (2) HSIL and cervical cancer group as the observation group. We used the ROC curve to evaluate the diagnostic efficacy of the test method. After calculating the Youden index and determining its grouping threshold, it is HPV16 E7 oncoprotein concentration = 8.68 ng/ml, which can be used as a critical value to distinguish LSIL and HSIL. The results showed that the test method has good accuracy in distinguishing normal cervix, LSIL from HSIL and cervical cancer, suggesting that the method is reliable.
A large number of studies have confirmed that for the screening of high-grade cervical lesions, the sensitivity of HPV DNA detection is high and the specificity is insufficient while the specificity of TCT screening is high but the sensitivity is significantly reduced, resulting in partial missed diagnosis of HSIL[18, 19]. At the same time, studies have shown that the HPV E7 oncoprotein or mRNA assay has a higher specificity and positive predictive value than the HPV DNA assay and thus has a higher diagnostic value for the diagnosis of high-grade cervical lesions including HSIL and cervical cancer.
In the second part of the study, we used a prospective study to verify the value of HPV16 E7 oncoprotein in the diagnosis of cervical lesions. It showed that the positive result of E7 oncoprotein had a hint effect on HSIL. And the sensitivity, specificity, positive predictive value, and negative predictive value of HPV16 E7 oncoprotein detection for HSIL and cervical cancer were: 87.14%, 70.00%, 87.14%, and 70.00%. A systematic review report by Burger et al. shows that the sensitivity of HPV DNA detection is 70%-100% and the specificity is only 28%-56%, while the Aptima mRNA detection approved by the FDA for clinical use in cytology is ASC-US population, the sensitivity is 91%-95% and the specificity is 42–61%. Another research showed that the sensitivity is 91.4% and the specificity is 46.2% of Aptima mRNA . The second-generation Hybrid Capture Technology (HC-2) specification showed that the sensitivity, specificity, positive predictive value, and negative predictive value of high-grade cervical intraepithelial lesions and cervical cancer were diagnosed in patients with Pap smear diagnosed as ASC-US were: 93.0%, 61.1%, 17.2%, 99.0%. Compared with HPV DNA and HPV mRNA detection methods, the HPV E7 oncoprotein assay used in this study has a higher specificity and positive predictive value. At the same time, its sensitivity and negative predictive value are not significantly reduced. This suggests that HPV E7 oncoprotein detection is a method with a higher diagnostic value, and it is expected to become a new indicator for cervical precancerous lesions and cervical cancer screening.
Previous studies have shown that HPV E6/E7 oncoprotein detection has better sensitivity than TCT detection, and has better specificity than HPV E6/E7 mRNA and HPV DNA detection. Studies have also shown that HPV E6/E7 oncoprotein detection is more sensitive than HPV E6/E7 mRNA detection in HPV16 and HPV18 infected patients, 71.3% and 56.3%, respectively. At the same time, studies have pointed out that in high-grade cervical intraepithelial lesions and cervical cancer, HPV E6/E7 oncoprotein detection compared to HPV E6/E7 mRNA detection, the difference in sensitivity between the two was not statistically significant, and HPV E6/ The E7 oncoprotein assay has high specificity and positive predictive value.
In our research, the sensitivity, specificity, positive predictive value, and negative predictive value of the HPV16 E7 oncoprotein assay were higher than those of the TCT assay, which is consistent with previous research results. The consistency between HPV16 E7 oncoprotein examination and pathological examination was higher than that of TCT examination. It suggests that it has better diagnostic application value than TCT detection. The positive predictive value and negative predictive value of HPV16 E7 oncoprotein detection for high grade and above lesions as high as 87.14%, 70.00%, suggesting it can be used as a colposcope shunt method to reduce unnecessary colposcopy referral. In addition, due to the need for professional cytopathologists to determine the results of TCT testing, it caused high missed diagnosis and misdiagnosis in some underdeveloped areas. For these areas, it should consider the use of HPV E7 oncoprotein detection instead of TCT for cervical cancer screening.
Looking for potential biomarkers can help us identify patients with high risk of disease progression, and early intervention for these patients can effectively reduce the incidence of cervical cancer. The results suggest that the detection of E7 oncoprotein has a good diagnostic effect in predicting the progression of lesions, and the detection of E7 oncoprotein is helpful to predict the prognosis of patients with known HPV16 infection. For the patients with high detection level of E7 oncoprotein, it is necessary to strengthen the screening intensity or even give active treatment. Compared with known prognostic markers such as p16, ki67, hTERC gene, E7 oncoprotein is more convenient and economical. However, there are too few cases in the study and further studies are needed.
In summary, the HPV16 E7 oncoprotein detection method used in this study is accurate, reliable, and easy to obtain. The method is novel and can be semi-quantitatively tested. At the same time, HPV16 E7 oncoprotein concentration of 8.68 ng/ml can be used as a critical value to distinguish between HSIL and cervical cancer and there was high specificity and positive predictive value with no significant decrease in sensitivity and negative predictive value, suggesting that HPV E7 oncoprotein detection has more diagnostic values. It can be used as a colposcopy shunt method. And it also has a good predictive value for the prognosis of LSIL and below lesions. It is expected to be widely used for the clinical detection of cervical lesions and become a new indicator of precancerous cervical lesions and cervical cancer screening.
In addition, since this study only tested the E7 oncoprotein of HPV Type 16, a large-scale, multicenter study of the oncoproteins of all high-risk HPV types is still needed to evaluate the value of HPV E7 oncoprotein detection in cervical lesion screening.