The American Cancer Society estimates 7,060 new cases of anal cancer will be diagnosed in 2013, with 4,430 occurring in women.1 Incidence of anal cancer has continued to rise over the past 20–30 years as incidence in women has risen 41% from 1975–1984 to 1995–2004.2 As the incidence of anal cancer continues to increase, anal intraepithelial neoplasia screening has become a burgeoning field of interest. Anal intraepithelial neoplasia is felt to be a precursor to anal cancer, analogous to cervical intraepithelial neoplasia (CIN) and cervical cancer. Currently, the frequency of progression of high-grade anal intraepithelial neoplasia to anal squamous cell cancer is not fully elucidated, but it is estimated to be in the range of 8.5–13%.3,4
Screening guidelines are limited for anal intraepithelial neoplasia5; the majority focus on men who have sex with men, particularly those with the human immunodeficiency virus (HIV), and center on anal cytology. In this population, anal cytology has demonstrated a sensitivity of approximately 69–93%.6 Unfortunately, when applied to the female population, we have demonstrated very poor sensitivity of anal cytology.7,8 The higher sensitivity reported in the population of men with or without HIV who have sex with men is most likely the result of the large burden of disease seen in this population. Another plausible cause is an overestimation of sensitivity if anoscopy was not used on those with negative cytology. Given the poor sensitivity of cytology in heterosexual women, improved screening modalities are needed.
High-resolution anoscopy with directed biopsy can be used to diagnosis and treat anal intraepithelial neoplasia before it becomes macroscopic. High-resolution anoscopy as an initial screening tool is limited by the invasive nature of the examination and the limited resources and persons trained in anoscopy. Therefore, a valid and reliable clinical assessment method is needed to identify those individuals who are at risk for anal intraepithelial neoplasia and would be appropriate for high-resolution anoscopy. We wished to study the risk factors for anal intraepithelial neoplasia in women and develop a model to assess anal intraepithelial neoplasia risk.
PATIENTS AND METHODS
This is a prospective cohort of consecutive patients with genital (vulvar, vaginal, or cervical) intraepithelial neoplasia referred to the University of Tennessee—West Clinic gynecologic oncology division from June 2006 to December 2010.
The study was approved by the institutional review board at the University of Tennessee Health Science Center. Patients were included in the study if they had a biopsy-confirmed diagnosis of genital intraepithelial neoplasia (vulvar, vagina, or cervical) and were agreeable to indicated anal biopsies. Patients were excluded if they had a history of any anogenital cancer (cervical, vulvar, vaginal, or anal) before evaluation. One gynecologic oncologist who was trained in high-resolution anoscopy evaluated all eligible patients. Medical history, sexual history, and demographic data were collected directly by the physician during the initial visit. Any unique identifiers were deleted to protect patients' privacy.
The lower genital tract evaluation protocol has been described previously.7 Briefly, vulvar, vaginal, and cervical examinations were done in the usual dorsolithomy position using cytology and colposcopy. Next, anal cytology was obtained and processed using a liquid-based cytology technique. High-resolution anoscopy was then performed using a plastic disposable anoscope and 3% acetic acid. Any abnormalities (eg, acetowhite changes, raised lesions, discolorations) were biopsied. A local anesthetic (lidocaine 1% without epinephrine) was injected before biopsy of lesions distal to the dentate line. Digital vaginal and rectal examinations also were performed after colposcopy and anoscopy.
Associations between variables and anal intraepithelial neoplasia were evaluated with univariate logistic regression. Odds ratios were calculated for statistically significant variables. Results of these analyses allowed for the identification of individual variables from the original group of variables that had a strong association with anal intraepithelial neoplasia. Spearman correlations among pairs of these variables were calculated to detect similar variables as well as those that had little overlap.
The bivariate analysis was used to identify individual variables that were predictive of anal intraepithelial neoplasia. Because it was probable that a combination of variables would improve the prediction of having anal intraepithelial neoplasia, a regression analysis was also carried out to identify any combinations of variables that would be superior to any single variable for predicting anal intraepithelial neoplasia. We carried out logistic regression analysis using a forward stepwise procedure with anal intraepithelial neoplasia as the dependent variable. The groups of variables with strong associations with anal intraepithelial neoplasia were the independent variables. The regression analysis yielded a model for the probability of having anal intraepithelial neoplasia. Sensitivity and specificity in predicting anal intraepithelial neoplasia status were calculated for this model. Sensitivity and specificity were also calculated for logistic regression models with each of several risk factors considered separately. For the purposes of our study, sensitivity and specificity were defined as the percentage of persons with anal intraepithelial neoplasia who were correctly classified.
All eligible participants were included and no a priori sample size was calculated. P<.05 was considered statistically significant. IBM SPSS Statistics 20 and JMP Pro 10.0 software were used for statistical analysis.
Three hundred thirty-one patients were initially identified for the study; two declined anal examination and two declined anal biopsy after anoscopy. The remaining 327 patients were eligible for analysis (Fig. 1). Fifteen patients did not undergo cytology as a result of incidental deviation from the protocol and were not included in comparative analysis of anal cytology to anoscopy. All participants were heterosexual women with a median age of 39 years (median absolute deviation of 12 years). Twenty-eight (8.5%) patients were immunocompromised (16 HIV, seven autoimmune disorders, four on suppression for organ transplantation, and one with both autoimmune disorder and organ transplant). No participants were lost to follow-up because all information and indicated biopsies were collected at the time of entry.
Of 327 patients, 137 (41.9%) had abnormal anoscopy and received directed biopsies (Fig. 1). Of those biopsied, 67 (51%) had a disease state identified: 64 (46.7%) patients with anal intraepithelial neoplasia (36 stage I, six stage II, 22 stage III), five with nonanal intraepithelial neoplasia abnormalities (one Candida infection, one lichen sclerosis, and three lichen simplex chronicus), and one gastrointestinal stromal tumor. Prevalence of anal intraepithelial neoplasia in this study was 19.6% (64 of 327 patients). Sensitivity (11.9%, 0.053–0.23) and specificity (95.7%, 0.92–0.98) were calculated for anal cytology. Cohen's κ coefficient was then calculated to assess the agreement of anal cytology to anoscopy and anal cytology to biopsy results. The κ statistic was 0.089 (95% confidence interval [CI] 0.022–0.15) and 0.1 (95% CI −0.01 to −0.22), respectively, indicating poor agreement of anal cytology with anoscopy and biopsy results. The multifocal nature of genital dysplasia was demonstrated in this study. Of the 65 patients with anal intraepithelial neoplasia, 48 (73.8%) had vulvar dysplasia, 10 (15.4%) had vaginal dysplasia, and 14 (21.5%) had cervical dysplasia.
Nine risk factors were originally considered as possible predictors of anal intraepithelial neoplasia based on a review of the literature. These factors are shown in Table 1. Univariate logistic regression demonstrated statistical significance for smoking history, vulvar intraepithelial neoplasia (VIN), immunosuppression, history of anal sex, and multiple sexual partners. As four sexual partners was the median for the sample, more than four lifetime sexual partners was used to define multiple sexual partners. Women did not differ significantly with regard to age, race, or presence of vaginal intraepithelial neoplasia or CIN (Table 1). Vulvar intraepithelial neoplasia was further analyzed by stage and remained significant for vaginal intraepithelial neoplasia I and III. Vaginal intraepithelial neoplasia and CIN were also further analyzed by stage and remained nonsignificant. The risk factors that were significantly associated with anal intraepithelial neoplasia were also correlated with one another (Table 2). Significant Spearman correlations were found among three clinical variables. The highest correlation (r=0.21) was found between VIN and immunosuppression.
A predictive model of anal intraepithelial neoplasia was constructed using a forward stepwise logistic regression analysis. The variables used for this model were those in Table 1 with P<.05: smoking history, VIN, multiple sexual partners, immunosuppression, and history of anal sex. Age was found to be a borderline univariate predictor of anal intraepithelial neoplasia and was entered as a covariate in the final model preliminarily. Adjusted odds ratio for age remained nonsignificant (P=.156) and did not change the adjusted odds ratios for the other variables in Table 3.
The final model (Table 3) included history of anal sex, immunosuppression, and VIN. This model would predict that an individual with no history of anal sex, immunosuppression, or VIN would have a predicted probability of anal intraepithelial neoplasia of 9%. Conversely, an individual with a positive history for all three would have a predicted probability of anal intraepithelial neoplasia of 71.8%.
The receiver operating characteristic curve was obtained by plot of the presence of zero, one, two, or three risk factors with an area under the curve of 0.708. The best cutoff that jointly maximized both sensitivity and specificity is a predicted probability of 38.8% for anal intraepithelial neoplasia. This cutoff value correlated to the presence of any two risk factors and resulted in a negative predictive value of 88.2% (95% CI 0.83–0.92) and positive predictive value of 43.1% (95% CI 0.31–0.56). Predictive values, sensitivity, and specificity for individual risk factors as well as the final model are shown in Table 4.
Evidence regarding the origin of anal cancer has been increasing. No longer is the origin felt to be attributable to hemorrhoids, fissures, or inflammatory bowel disease9 but rather to human papillomavirus infection, increased lifetime number of sexual partners, genital warts, cigarette smoking, receptive anal intercourse, and HIV infection.10 Anal squamous cell cancer appears to have an identifiable, preinvasive stage similar to that of other genital intraepithelial neoplasias.11 This is important, because 25% of newly diagnosed anal canal carcinomas are larger than 5 cm in diameter and clinically node-positive.12 The great success story of cervical cancer screening and the application of colposcopy to the vulva and vagina herald the need to screen for anal intraepithelial neoplasia.
This study demonstrates the low sensitivity and poor correlation of anal cytology and serves to establish the role of anoscopy in identifying the presence or absence of anal intraepithelial neoplasia. The purpose of this study was to identify risk factors for anal intraepithelial neoplasia in a female population and develop a model for quantifying the risk of anal intraepithelial neoplasia in women. The need to accurately and reliably quantify anal intraepithelial neoplasia risk is based on the assumption that anal intraepithelial neoplasia is a precursor to anal cancer and that adequate identification and treatment, through referral of individuals at high risk to anoscopy, can prevent the development of anal cancer.
Analysis revealed five factors significant for anal intraepithelial neoplasia: smoking history, VIN, multiple sexual partners, immunosuppression, and history of anal sex. Our results did not show age, race, CIN, or vaginal intraepithelial neoplasia to be significant risk factors for anal intraepithelial neoplasia. The significance of VIN and not CIN or vaginal intraepithelial neoplasia, combined with the lack of correlation between smoking and VIN, may indicate that proximity of dysplasia to the anus, rather than the mechanism of disease, is a more important factor in the development of anal intraepithelial neoplasia.
The model with the best sensitivity and specificity for prediction of anal intraepithelial neoplasia included three factors: history of anal sex, immunosuppression, and VIN. Using the presence of two or more factors, this model had a sensitivity of 47% and specificity of 86.2%. Thus, 28 of 56 persons with anal intraepithelial neoplasia and 135 of 166 persons without anal intraepithelial neoplasia were correctly identified. The sensitivity and specificity were superior to any of the clinical variables used in isolation. This preliminary study has shown a promising method for quantifying anal intraepithelial neoplasia risk. Results from this initial study need to be confirmed with a larger community-based population.
Advantages of this study include the use of both anoscopy and anal cytology to calculate the sensitivity of anal cytology. Other studies have been subject to verification bias because participants with negative anal cytology did not receive anoscopy, resulting in an overestimation of the sensitivity of anal cytology. Although the study population had a high prevalence of genital dysplasia, the similar prevalence of anal intercourse (32% compared with 36%, respectively) and median number of sexual partners (four) to that identified in the national health statistics report makes it more applicable to the general population.13 Furthermore, our study contained only 28 (8.5%) patients who were immunocompromised.
Limitations of this study include the absence of a priori sample size and power calculation. Therefore, nonsignificant results could be the result of a lack of statistical power rather than a true null association. The lack of studies in the female population makes sample size calculation difficult. This study may serve to aid future studies in this regard. Second, many other confounding factors, suspected or yet unknown, may also contribute to anal intraepithelial neoplasia and are not accounted for in this study. Third, women with a normal result on high-resolution anoscopy were not submitted to random biopsies; for this reason, lesions could be missed, and the findings might be underestimated. Lastly, screening procedures were done by one gynecologic oncologist, which may have limited the application of the result to other populations and practices and may have confounded the results because of the skill level of this individual. On the other hand, a single gynecologic oncologist conducting all of the cytology specimen collections and anoscopy reduced any interobserver variability.
In summary, anal squamous cell cancer is a growing problem among women. Screening for anal intraepithelial neoplasia with cytology alone in females with genital dysplasia has poor sensitivity and very poor correlation with anoscopy. Our study has developed a simple predictive model based on the presence of any two of three risk factors for anal intraepithelial neoplasia (vulvar dysplasia, immunosuppression, and history of anal sex) to identify women at increased risk of having anal intraepithelial neoplasia. These women may benefit from high-resolution anoscopy to screen for anal intraepithelial neoplasia.
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© 2013 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.
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