The sensitivity of cervical smears for adenocarcinoma in situ (AIS) is not known, nor is it known whether false-negative smears are due to sampling or to screening or interpretive errors. In 16 of 34 patients with AIS, 38 negative smears were reported 2 weeks to 7 years before biopsy. Thirty-one of these negative smears were rescreened, and 17 (55%) were retrospectively diagnosed as abnormal. The purpose of this study was to obtain an estimate of Pap smear sensitivity for AIS and to uncover difficulties in interpretation of smears that may have led to false-negative diagnoses. MATERIALS AND METHODS The surgical p a t h o l o g y files of Brigham andWomen's Hospital, Boston, were searched for case reports of AIS or AIS combined with squamous cervical intraepithelial neoplasia (CIN) with a complete cone biopsy, hysterectomy, or both for the years 1986 to 1995. All available smears diagnosed as negative before an initial biopsy confirming AIS were confirmed sampling errors. The sensitivity of cervical smears for AIS was 55% to 72%. Improved sampling of the endocervical canal offers cytologists the opportunity to diagnose AIS. This study demonstrates that this opportunity may not be fully exploited. Small "endometrioid" AIS cells and AIS cells resembling reactive endocervical cells may be mistaken for benign cells, thus decreasing sensitivity.

A b s t r a c t Rapid (30-second) prescreening of cervicovaginal smears can be used to detect false-negative cases and determine the false-negative rate of primary screening, hut the performance characteristics have not been evaluated fully. A test set of 242 cases includingRapid prescreening of cervicovaginal smears is a quality control measure that has been practiced predominantly in the United Kingdom. Unlike the rescreening of 10% of cervicovaginal smears that is required of laboratories in the United States, this method involves prescreening 100% of all smears, but for only 30 seconds each. The results of this prescreening are recorded and used to identify any falsenegative cases that result from the full screening that occurs subsequently. Although the sensitivity of rapidly prescreening a case is lower than that of traditional screening without a time limit, rapid prescreening allows more cases to be reviewed in the same amount of time, which results in the detection of more false-negative cases compared with 10% rescreening.'~5 For example, the sensitivity of rapid screening for a diagnosis of atypical squamous cells of undetermined significance (ASCUS) is only about 30% to 50% that of routine screening or rescreening. 35 -6 But because rapid screening is approximately 5 to 10 times faster than routine rescreening, it detects more false-negative cases than does routine rescreening.In addition, rapid prescreening is a better method than routine rescreening for determining the false-negative rate (FNR) of primary screening. To accurately measure the FNR. it is necessary to determine the FNR of the method used to find false-negative cases, whether routine rescreening or rapid prescreening.7 Since rapid prescreening, by design, includes a review of all specimens, both positive and negative, the positive specimens can be used as controls to calculate the FNR. By contrast, incorporating known positive controls in routine rescreening is difficult and may not be practical. Nevertheless, the performance characteristics of rapid screening have not been completely characterized. Although

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