Cytologic features of squamous cell carcinoma in ThinPrep slides: evaluation of cases that performed poorly versus those that performed well in the College of American Pathologists Interlaboratory Comparison Program in Cervicovaginal Cytology.

CONTEXT: Although the cytologic features of squamous cell carcinoma in ThinPrep specimens are well known, whether these features are different in cases that are easily identified than in cases that are more difficult to identify is not known.

OBJECTIVE

To determine the cytologic features of squamous cell carcinoma in ThinPrep specimens that are easy to identify versus those that are difficult.

DESIGN

The cytologic features of 6 cases of squamous cell carcinoma that performed poorly in the College of American Pathologists Interlaboratory Comparison Program were compared with 14 cases that performed extremely well.

RESULTS

After evaluation of multiple criteria, 7 different cytologic features were analyzed based on review by a consensus panel blinded to the performance of the cases. The feature that was most strongly associated with cases that performed poorly was the presence of Trichomonas vaginalis (5/6 [83%] vs 0/14; P <.001). The presence of marked nuclear pleomorphism was more common in cases that performed well (4/14 [28%] vs 0/6; P =.27), but was not significant. The number of tumor cells, the number of normal cells, and the presence of keratinization, pleomorphism, nucleoli, and diathesis were not significant. The most common misdiagnosis after Trichomonas vaginalis was reparative change.

CONCLUSIONS

The presence of Trichomonas is characteristic of cases of squamous cell carcinoma in ThinPrep slides that are often misdiagnosed in this program. While Trichomonas is identified by participants in some of these cases, a significant percentage of participants interpreted the findings as reparative, without identifying the organism. These results emphasize the importance of distracting factors, whether identified or not, in evaluating gynecologic cytology.