Cytology of spontaneous nipple discharge--is it worth it? Performance of nipple discharge preparations in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytopathology.

Context: The usefulness of spontaneous nipple discharge analysis is controversial. Nipple discharge preparations are rare in clinical practice and malignant cases are exceptional. The College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytopathology has included nipple discharge preparations since its inception.

Objectives: To evaluate participant responses in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytopathology to assess the accuracy of cytologic interpretation of nipple discharge preparation.

Design: General diagnostic category (benign, suspicious, malignant), participant type (pathologist, cytotechnologist), stain (Papanicolaou, modified Giemsa), and program year (2005-2009) were analyzed using χ(2) and a nonlinear mixed model for slide factor correlation structure.

Results: Of 2506 responses, 1280 (51%) were malignant, 171 (7%) were papillary, and 1055 (42%) were benign. There were 222 discordant general category responses with a false-positive/suspicious rate of 12.8% and a false-negative rate of 3.4%. The most common false-negative diagnosis was mastitis/abscess (125 of 1272 responses; 9.8%). The most common false-positive response was papillary lesion (26 of 457 responses; 5.7%). There were no differences between stains or years. Cytotechnologists performed better than pathologists; pathologists had a higher false-negative rate than cytotechnologists (15.3% versus 7.9%, P < .001).

Conclusions: There is poor accuracy in evaluating nipple discharge preparation in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytopathology. If the findings in the program parallel clinical practice, nipple discharge preparations may adversely impact patient care. A benign nipple discharge cytologic diagnosis does not exclude malignancy, and the false-positive/suspicious rate requires confirmation of a malignant nipple discharge prior to definitive patient management.