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Cytology in parotid Warthin's tumors: Methodological issues on diagnostic value to avoid misinterpretation

Dear Editor, I read the article entitled “The diagnostic value of cytology in parotid Warthin's tumors: international multicenter series.” by Borsetto et al published in Head Neck 2019. Warthin's tumor (WT) is a common benign salivary gland neoplasm with a negligible risk of malignant transformation. However, there is a risk of malignant tumors being misdiagnosed as WT on cytology and inappropriately managed conservatively. The aim of the authors was to determine the diagnostic value of cytology in parotid WTs. Patients from nine centers in Italy and the United Kingdom undergoing parotid surgery for cytologically diagnosed WT were included in this multicenter retrospective series. Definitive histology was compared with preoperative cytological diagnoses. Based on their results, in 88.9%, the final histological diagnosis was WT. In 21 cases (4.2%), a malignant neoplasm was diagnosed, which had been incorrectly labeled as WT on cytology. They concluded that the risk of undiagnosed malignancy should be balanced against surgical risks when considering the management of WT. However, there are methodological issues, which can considerably affect the main message of the study. First, given the information in the paper, the number of the true negatives was not mentioned; therefore, specificity and accuracy of cytology cannot be calculated. The most appropriate estimates to evaluate accuracy of a single test such as cytology compared to histopathology are sensitivity (Sen), specificity (Spe), positive predictive value (PPV), negative predictive value (NPV), likelihood ratio positive (ranging from 1 to infinity; the higher the LR+, the more accurate the test), likelihood ratio negative (ranging from 0 to 1; the lower the LR−, the more accurate the test), as well as accuracy and odds ratio (ratio of true to false results). According to their results, we have undefined estimates for accuracy parameters. It is good to know that sensitivity is an important measure in public health aspects instead of clinical fields. Likewise, PPV and NPV are among measures which are more appropriate for advice about the accuracy of a diagnostic test for clinical purposes. Therefore, I suggest applying predictive values, likelihood ratios, odds ratios, and diagnostic accuracy to decide about the accuracy of cytology. Moreover, predictive values are dependent on several factors including disease prevalence, sensitivity, and specificity of a test. As the prevalence of the outcome changes, the PPV of the test can easily be affected. Accordingly, the author should consider and maybe report the disease prevalence while deriving the results of the study. Second, what is critically important is considering that accurate diagnosis is very important because of the correct management in people who are truly positive; likewise, operating surgery will have inconvenient effects. One of the vital facts that are neglected in this article is the importance of false-positive and particularly false-negative and considering the consequences of this neglection. It must have made authors think of “it might be extremely important when the test diagnoses a person as negative while it is positive (false negative)” so that percent of false-negative and specially NPV becomes strikingly critical to consider, calculate correctly, and report in these cases. Further more, I redraw the two by two table to calculate accuracy estimates.