A Multicenter, Randomized Controlled Trial of the Efficacy, Safety and Immunogenicity of HPV Vaccination in Preventing Recurrence of HSIL in HIV-positive MSM

Advances in the treatment of HIV-infected individuals with the advent of the combination antiretroviral therapy (cART) era has led to dramatic reductions in mortality and morbidity. These dramatic strides in survival within HIV-positive populations have led to a focus on longer-term morbidities in these individuals, including malignancies. Indeed, an increase in a variety of malignancies in HIV-infected individuals has been noted in the cART era. Amongst these are cancers associated with HPV, responsible for the vast majority of cervical cancers (itself a well-established acquired immune deficiency syndrome (AIDS)-defining illness), and 40-90% of anal, vulvar, vaginal, penile, and oropharyngeal cancers. More specifically, a recent meta-analysis indicates that the overall prevalence of HPV in anal carcinoma is approximately 84%, with HPV type 16 being isolated in 73% of all cases, making it the most prevalent type implicated in anal carcinoma.

Though infrequent at a rate of one per 100 000, squamous cell anal carcinoma is on the rise in the general population. It occurs at significantly higher rates in HIV-positive men - particularly among MSM - with an estimated rate of 60 to 160 per 100 000. A recent study of thirteen North American AIDS Cohort Collaboration on Research and Design (NA-ACCORD) with over 34,000 HIV-infected patients, found that anal cancer rates were highest in HIV-infected MSM, with a rate of 131 per 100,000 person years. In fact, rates of anal cancer among HIV-infected MSM are comparable to rates of cervical cancer in women prior to the adoption of routine screening for cervical dysplasia. In addition to its etiologic association with HPV, anal cancer shares many similarities with cervical cancer. Both are squamous cell cancers occurring at the squamo-columnar junction, and both likely arise from histologically-similar, dysplastic precursor lesions. It is postulated that a critical step in anal cancer carcinogenesis is the establishment of persistent infection (conventionally defined as greater than six or twelve months) with oncogenic HPV in the anal canal. Though the majority of HPV infections are considered transient and will eventually clear even in HIV-positive individuals, HIV-positive individuals have higher rates of persistent infection, especially with oncogenic HPV types.

Of the greater than 170 HPV types, over 30 favour the anogenital area, and on the basis of epidemiologic and phylogenetic data, these have been classified by the International Agency for Research on Cancer (IARC).

The vast majority of anal cancers (as well as cervical cancers) are caused by two high-risk HPV types: HPV type 16 and HPV type 18, felt to be responsible for 66% and 5% of anal cancers, respectively. However, a recent study from France examining the distribution of HPV types in cases of anal cancer found even more dramatic results: HPV was found in 96.7% of all cases, with HPV-16 being the most prevalent type (75%), with other high risk types (HPV-18, -52, -33, and -51) found in 4% to 6% of cases. Further, HPV-16 and -18 - either alone or in combination - were found in over 78% of cases. HPV lesions caused by low-risk types include condylomata (or commonly known as 'genital warts'), of which 90% are caused by HPV types 6 and 11.

Prevention strategies for anal cancers have emerged that are analogous to strategies used in cervical cancer screening, that rely on a combination of cytology (Papanicolaou, or Pap smear) and high-resolution anoscopy (HRA; analogous to colposcopy), both of which screen for high-grade anal intraepithelial neoplasia (HGAIN; typically graded as anal intraepithelial neoplasia (AIN) AIN-2 or -3). Despite the clear evidence indicating the benefit of screening and treatment procedures in cervical cancer screening, no large rigorous studies have been performed to assess the performance of such strategies in anal cancer screening in either men or women.