Introduction

During the last two decades the incidence of anal cancer in the HIV-infected population has increased significantly [1,2], especially among HIV+ men who have sex with men (MSM), with incidence rates between 65 and 109 per 100,000 person year[3]. This is much higher than the incidence of cervical cancer in HIV negative women before standard cytological screening was introduced [4], and therefore routine screening for anal premalignant lesions is subject of discussion. In analogy with cervical intraepithelial neoplasia (CIN), premalignant anal lesions are called anal intraepithelial neoplasia (AIN), graded as AIN 1 (low grade (LG)AIN) and AIN 2/3 (high grade (HG)AIN). AIN is present in the majority of HIV+ men who have sex with men (MSM). AIN of any grade is found in 68%-81%, HGAIN in 25-52% [5-7]. For HGAIN, progression rates to anal cancer have been reported to be 14% and 16% among HIV+ MSM, with median follow-up periods of 2 and 5 years respectively [8,9].

Like in CIN, screening and treatment of AIN may be helpful to prevent the development of cancer. The gold standard for AIN detection is high resolution anoscopy (HRA) with biopsies of suspect lesions [10]. Given the high prevalence of HGAIN and low specificity of anal cytology [7], HRA in combination with histopathological examination of lesional biopsies is the preferable first line (HG)AIN screening method.

Since HRA is time consuming and therefore expensive, not generally available and cumbersome for the patient, it would be useful to identify risk factors for AIN, in order to identify a high-risk population. Previous studies addressing this question used cytological abnormalities as endpoint or cytology as first screening step before HRA [11-18]. The main risk factors identified were receptive anal intercourse (RAI) and HIV infection. The outcomes on other risk factors were conflicting. Two studies performed HRA as primary screening method [19,20]. The presence of high-risk HPV types, in particular HPV16, was a significant risk factor [20]. However, testing for the presence of high-risk HPV types is expensive and not generally available. In addition, these studies did not evaluate other potential risk factors like sexually transmitted infections (STI), anal enemas, sexual habits and drug use, and one of the two only included patients who were HPV 16 positive [19].

In the present study, we investigated a wide range of potential risk factors for AIN, with HRA as primary screening tool. Our goal was to identify factors that might help to identify HIV+ MSM at greatest risk for having premalignant anal (AIN) lesions.

Methods

Results

Discussion

In this study, we analysed a wide range of potential risk factors for AIN and HGAIN in 311 HIV+ MSM. The goal was to identify a high-risk subgroup in order to target future screening programs more efficiently. This is the largest study of its kind in the cART era and the first study in which HRA as primary screening method (without preceding cytology) is combined with both medical history and detailed questionnaires addressing sexual habits and substance use.

AIN was found in 56% and HGAIN in 30% of 311 participants. In a multivariable analysis, duration of cART and anal XTC use were negatively associated with AIN and GHB significantly increased the risk for AIN. However, a combined multivariable predictor of these three parameters showed that in only 3 % of patients screening could be skipped. No parameters were significantly associated with HGAIN.

The negative association of duration of cART use with AIN is in line with two recent studies in which HRA was also used as primary AIN screening method. The first study showed a lower risk for AIN 2-3 in men using cART: an odds ratio (OR) of 0.28 for receiving cART > 4 years [20]. The second study, which reported odd ratios in relation to absence of AIN instead of presence, showed a positive association of the use of cART (but not duration of cART) with the absence of AIN, with an OR of 2.28 (p=0.045) [25]. However, this study found an AIN-prevalence among HIV+ MSM of only 16%, which is remarkably low given the current epidemiological data on AIN [3]. Two studies with cytology as primary screening method also reported a relation with cART. The first study showed an OR of 0.18 for receiving cART[17], but in the latter study it was found that in only 4% of patients high grade lesions regressed after initiating cART [14].Other studies do not show any beneficial effect of ART on AIN [11,12,15,16,19]. Likewise, contradictory results are reported on the influence of cART on CIN in HIV positive women [26-28]. In contrast to the influence of cART, we did not find any association between presence of AIN and the CD4 count, suggesting that the benefit of cART is not directly mediated by immune restoration as measured by CD4+ cells. Also, we did not find an association with nadir CD4+ cell count. Some previous studies showed a significant correlation between a low nadir CD4 count and AIN [12,15,20], whereas other studies did not [11,16,19].

Besides cART use, also anal XTC use (ever) was negatively associated with AIN. Anal administration of XTC consists of injecting XTC dissolved in water with a blunt syringe into the anal canal/distal rectum. We did not find any data on mucosal effects of XTC. However, XTC is known to have immune-inhibitory rather than immune stimulating effects [29]. Given the low absolute number of patients reporting anal XTC (n=12), we suspect that the ‘protective’ effect of anal XTC use is most likely a coincident finding. One previous study looked into anal drug use in general, but did not find an association [18].

Although there was a suggestion of increased risk of AIN with a history of (non anal) XTC and amphetamine use, the only recreational drug that showed a significant association with AIN was GHB. GHB is known to have strong disinhibiting behavioural and sexual arousal effects [30]. This might result in more risky sexual behaviour. However, we did not see any influence of GHB use on the number of RAI partners. Therefore, if there is a connection with increased risk behaviour, this might be explained by more unprotected sex and resulting increased exposure to HPV. However, this is speculative since we did not collect data on condom use.

Participants who reported more than 50 anal enemas in their life showed a (non-significant) higher risk for HGAIN. One previous study analysed enema use as a potential risk factor, but did not find an association with AIN [18]. Other studies showed that enema use is significantly associated with lymphogranuloma venereum proctitis, hepatitis B and hepatitis C infection [31-33]. Usually, the enemas contain water, and no irritant substances [31], suggesting that the irrigation procedure itself increases the risk of pathogen transmission, possibly through disruption of the mucosal barrier. Also, sharing of enema equipment with others might play a role. In the case of AIN, enema use might possibly facilitate the transmission of HPV.

Other characteristics, previous STIs, anal pathology, number of RAI partners, anal fisting, anal complaints and smoking were not associated with (HG)AIN. Various other studies investigated one or more of these, but none has been consistently identified as an important risk factor. Older age has been associated with an increased risk of AIN [20], but also the opposite has been found [17]. Although the increase in anal cancer is often attributed to an increased lifespan with HIV, duration since HIV diagnosis is not automatically associated with AIN [20]. Some studies showed a history of anogenital warts as a risk factor, but no other STI seems to be related to AIN [11,18]. Also data on number of sex partners are not conclusive [17,34]. To our knowledge one previous study collected data on anal fisting but, like in this study, did not find an association with AIN [18].

Strong points of our study are the use of HRA with biopsies as primary screening tool, the large number of unselected patients and the wide range of data collected.

Our study has also limitations. Although the physician who performed all HRA’s was sufficiently trained, lesions might have been missed. In that case, the prevalence found in our study is an underestimation. However, the AIN prevalence found is in line with previous data³. Further, we did not collect data on condom use. Condom use reduces the risk for anal HPV infection[36], but to our knowledge there are no data on a negative (or positive) correlation between condom use and the presence of AIN. Unsafe sex could also be a confounding factor for both GHB use and anal enemas. Finally, we did not analyse anal HPV. Our goal was to select a target population among HIV+ MSM based on readily available data and questionnaires, without any diagnostic procedure. It is possible that the detection of oncogenic HPV types, the number of HPV types or specific HPV types may contribute to identify those at risk for (HG)AIN. Two recent studies showed that subtyping and load determination of HPV in anal swabs can be useful in predicting (progression to) HGAIN [20,35]. Yet, the vast majority of HIV+ MSM carries multiple oncogenic HPV types [5,7] and HPV analysis is expensive and not generally available. Given the high prevalence of HGAIN, the contribution of HPV analysis needs further investigation, including an evaluation of its cost effectiveness. If only a limited proportion of HIV+ MSM can be excluded from HRA by performing HPV analyses, it might be cost-effective to skip this intermediate step and examine all HIV+ MSM by HRA.

In conclusion, we think that none of the risk factors we found will be useful to target future AIN screening programs in HIV+ MSM. The odds ratios we found were too small to reliably identify those with a low risk of AIN. Given the very high prevalence of HGAIN, screening seems warranted for all HIV+ MSM.