35. Accuracy of anal cytology in predicting histological HSIL: baseline results from the Australian Study of the Prevention of Anal Cancer (SPANC)

Background Anal cytology may form the basis of a future screening program to prevent anal carcinoma. Therefore, the accuracy of anal Papanicolaou tests in detecting histological HSIL needs to be evaluated. Methods: SPANC is a 3-year prospective study in homosexual men aged ≥35 years. At each of five visits, men undergo collection of a ThinPrep® anal cytological sample, high-resolution anoscopy (HRA) and biopsy of any abnormalities. Cytology is reported using the Bethesda system. Histology is reported using lower anogenital squamous terminology. Results: 351 men had a baseline visit by end July 2013. Median age was 49 (range: 35–79) years and 101 (28.8%) men were HIV positive. Anal cytology results were: unsatisfactory in 21 (6.0%), negative in 143 (40.7%), ASC-US in 51 (14.5%), LSIL in 22 (6.3%), ASC-H in 45 (12.8%) and HSIL in 69 (19.7%). 293 of 351 (83.5%) men had baseline histology. The most severe abnormality for each was: negative for SIL in 98 (33.4%), LSIL in 87 (29.7%) and HSIL in 108 (36.9%). Anal cytology sensitivity for histological HSIL (at ASC-US threshold) was 79.0%. Specificity was 53.8%. Positive predictive value (PPV) of any cytological abnormality for histological HSIL was 44.4% and PPV of HSIL cytoprediction was 63.8%. Negative predictive value (NPV) was 84.6%. Overall there was no significant difference between HIV positive and negative men with respect to sensitivity, specificity, PPV or NPV. Conclusions: These results indicate that histological HSIL is common in homosexual men. The finding of any cytological abnormality should prompt HRA. However, both cytology and HRA can miss or underestimate significant lesions in a single screening.