Assessing The Utility Of Anal Pap Smears For The Surveillance Of Peri-Anal/Anal Canal Carcinoma Following Definitive Radiation Therapy

To determine the value of routine anal pap smears for the surveillance of anal / peri-anal carcinoma following radiation therapy ± chemotherapy. Beginning in 2004 at the Indiana University Department of Radiation Oncology, anal canal brushings and peri-anal skin scrapings were obtained at each follow-up visit for all patients previously treated for carcinoma of the anal canal or peri-anal skin. Specimens were then analyzed using Thin-Prep liquid cytology. The records of all patients with at least one follow-up pap smear were reviewed, and the demographic and treatment characteristics, as well as the disease outcomes, were recorded. In those instances of abnormal cytology, further work up was performed, including exam-under-anesthesia or trans-rectal endoscopic ultra-sound, with biopsy when indicated. From 2004 - 2010, 36 patients with a diagnosis of peri-anal (6) or anal canal (30) cancer received radiation therapy as part of definitive treatment and subsequently had at least one anal pap smear performed during follow-up. AJCC T-Stage was as follows: Tis - 2, T1 - 3, T2 - 19, T3 - 10, T4 - 2. The median dose to the primary tumor was 50.4 Gy, with 11% and 89% receiving radiation alone and chemo-radiation, respectively. Median follow-up was 38.6 months (5 - 115), with a crude rate of local control of 91.6%. A total of 198 pap smears were performed, with a median of 3.5 (1 - 20) smears per patient. Seventy-two percent of patients had at least 1 abnormal smear, and 33% (66 / 198) of all smears were abnormal: 50% (33) - atypical squamous cells of uncertain significance (ASCUS), 42% (28) - low-grade squamous intra-epithelial lesion (LSIL), and 8% (5) - high-grade squamous intra-epithelial lesion (HSIL). Of the 3 patients with biopsy-confirmed local recurrence, 2 had a history of abnormal smears as early as 1 month (ASCUS) and 5 months (HSIL) prior to confirmation of local failure. No asymptomatic recurrences were detected as a result of abnormal anal cytology. Our initial experience does not support the use of routine anal pap smears for the surveillance of anal / peri-anal carcinoma following radiation therapy with or without chemotherapy. Considering the low rate of local failure and the high rate of abnormal cytology, potentially related to radiation treatment effect, the efficiency of routine anal cytology for the detection of asymptomatic local recurrence appears quite low. However, given the small sample size, further investigation may be warranted.