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OBJECTIVE: To assess the level of observer variability in the histologic identification of cutaneous T-cell lymphoma (CTCL) and its discrimination from diseases with similar histologic features. DESIGN: Cutaneous T-cell lymphoma specimens and randomly mixed controls were evaluated twice by 3 examiners. SETTINGS: The European Organization for Research and Treatment of Cancer (EORTC) Cutaneous Lymphoma Project Group. PATIENTS: The study was conducted with histologic specimens from 32 patients with mycosis fungoides (MF). In addition, 13 specimens of spongiotic, lichenoid, or psoriasiform simulators of MF were blindly and randomly mixed with the CTCL specimens as controls. MAIN OUTCOME MEASURES: To evaluate the accuracy and concordance among and individual reproducibility of raters of histologic diagnoses. RESULTS: Overall, the concordance among raters was fair to moderate (range, 0.283-0.562; weighted overall kappa, 0.412). Individual reproducibility of examiners ranged from moderate to almost perfect (range, 0.473-0.896; weighted overall kappa, 0.709) and was not significantly different for the definite lymphoma (range, 0.551-0.921; overall kappa, 0.802) and nonlymphoma (range, 0.368-0.950; overall kappa, 0.793) categories. Accuracy was similarly variable among raters: sensitivity ranged from 49.3% to 78.1% (overall kappa, 0.654), and specificity (control series) ranged from 46.2% to 69.2% (overall kappa, 0.595). Adding the diagnoses of probable lymphoma to those of definite lymphoma, sensitivity ranged between 73.5% and 84.9%. Although for each examiner there was a trend toward a lower sensitivity in the detection of early lesions compared with later lesions, the difference in sensitivity between the 2 groups was not statistically significant. CONCLUSIONS: The levels of concordance and reproducibility found in this investigation were similar to those obtained with comparable studies in the most varied fields of pathology, confirming that the identification of CTCL for our observers did not cause particular problems. Our findings also revealed that pitfalls in CTCL identification are not only limited to early lymphomatous lesions, as commonly postulated.
Marco Santucci (Sat,) studied this question.