Humoral response to HPV16 proteins in patients with anal high-grade squamous intraepithelial lesion and anal cancer
Considering the increasing incidence of human papillomavirus (HPV)-related anal cancer in the United States, a non-invasive screening strategy is warranted. Objective: To assess potential association of anal high-grade intraepithelial lesion (HSIL) or cancer with HPV16 antibody detection and estimate predictive ability of HPV16 antibody levels to determine HSIL or cancer status.
This is a case-control study that included 67 cases of anal HSIL, 116 cancer cases, and 830 population-based matched controls for age and gender from the State of Washington. Sera were analyzed for HPV16 antibodies to L1 and early proteins (E1, E2, E4, E6, E7) by multiplex serology assay. Association between HSIL or cancer and HPV16 antibody seropositivity were examined using logistic regression. Using classification tree (CART) and receiver operating characteristic analysis (ROC), we searched for HPV16 serological predictors of anal cancer.
Invasive cancer was more common in women (63% of cases were women) and HSIL was more common in men (54% of cases were men). The median age at anal cancer diagnosis was 58 years in women and 54 years in men. Compared to men with HSIL, women with HSIL tended to be older (median age 50 versus 43 years). HPV16 L1 seropositivity was present in 77% of persons with anal cancer, 88% in those with HSIL, and 31% in controls. HPV16 antibodies to early proteins were more common in invasive cancer cases (E1 24%, E2 46.6%, E4 38.8%, E6 43.1%, E 37.9%) than in those with HSIL (E1 4.5%, E2 19.4%, E4 29.9%, E6 13.4%, E7 37.3%) and controls (E1 3.1%, E2 21.9%, E4 23.5%, E6 7.8%, E7 24.8%). L1 seropositivity was more strongly associated with HSIL (aOR 20.6; 95% CI, 9.7 – 37.3) than invasive cancer (aOR 8.8; 95% CI, 5.3 – 15.2). Seropositivity to HPV16 antibodies early proteins was significantly associated with invasive cancer: E1 aOR 19 (95% CI, 9.1 – 41.4), E2 aOR 3.7 (95% CI, 2.4 – 5.9), E4 aOR 2.7 (95% CI, 1.7 – 4.2), E6 aOR 8.7 (95% CI, 5.1 – 14.7), E7 aOR 1.8 (95% CI, 1.1 – 2.8). Only E7 was associated with increased risk of HSIL (aOR 1.8; 95% CI, 1.0 – 3.1). Higher E6 antibody levels (MFI >800) was associated with a 94% risk of anal cancer in this case-control study. Predictive models adding serological factors (L1, E1, and E6) along with baseline risk factors (age, smoking status, and number of sex partners) improved prediction of anal cancer (AUC 90%; 95% CI, 87% - 93%) compared with baseline risk factors alone (AUC 80%; 95% CI, 76% - 84%).
HPV16 seropositivity to early proteins was higher among persons with invasive anal cancer than persons with HSIL or controls. Incorporation of HPV antibodies to classification algorithms significantly improved the ability to predict anal cancer in this sample of cases and controls.