Communicating risk for thyroid FNA: The pursuit of a better metric

Communicating the clinical significance of cytologic findings is a vital function of any cytology report. One of the key goals of developing uniform reporting systems, such as The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), is to provide a reproducible framework for conveying the clinical significance of each diagnostic category (ie, the associated risk) to clinicians and patients. This risk data should be readily understood and applicable to subsequent clinical decision making. Recent developments in the management of patients with thyroid nodules increasingly recognize the complex nature of thyroid neoplasia, in which the vast majority of tumors, including most “cancers,” pose little risk of patient mortality. This more nuanced approach to the clinical management of thyroid cancers should be matched by a similarly nuanced conveyance of risk in cytology reports, particularly for those specimens exhibiting “indeterminate” (TBSRTC categories III-V) findings. The challenge of communicating this complexity forms the basis for this discussion. The most common way of reporting risk in thyroid fine-needle aspiration (FNA) is via the risk of malignancy (ROM). ROM initially was introduced to allow for the more accurate comparison of the performance of individual cytopathologists and laboratories for both quality assurance and research purposes. ROM subsequently was incorporated into the first iteration of TBSRTC. Although ROM is statistically more accurately described as the positive predictive value for malignancy, clinicians and cytologists generally prefer the term ROM because it is easier for both they and their patients to understand. In most cases, patients interpret the ROM more colloquially as the risk of “cancer. ” Indeed, because its meaning is so easy to grasp, in clinical practice ROM routinely is used to help patients and clinicians select among different therapies. ROM also highlights areas in which TBSRTC can be improved, such as the criteria for nondiagnostic cases. In addition, ROM has been critical for understanding how best to incorporate ancillary testing into thyroid FNA. Despite its usefulness, ROM has significant limitations that may be overlooked. Accurate ROM figures require surgical pathology follow-up. For those categories in which the majority of patients do not undergo surgery, there are significant biases regarding which patients do undergo surgery and ROM must be inferred from the remaining population of patients who only are followed clinically. TBSRTC ROM figures represent the synthesis of ROM data published across institutions and may differ considerably from the ROM associated with individual laboratories or cytopathologists. Of particular note, there now is increasing recognition that many lesions diagnosed in the past as malignant have a very low risk of disease progression. This recognition recently led to the introduction of the term “noninvasive follicular thyroid neoplasm with papillary-like nuclear features” (NIFTP). The reported ROM of indeterminant thyroid FNA specimens has declined directly as a result of the adoption of NIFTP, thereby supporting the belief that ROM is a valid measure of risk in patients with indeterminant thyroid FNA specimens. At the same time, because NIFTP currently is considered to