Atypia of Undetermined Significance (AUS)

Abstract

In the MSRSGC, salivary gland FNA samples that are indefinite for neoplasms are classified as “Atypia of Undetermined Significance” (AUS). The AUS category reduces the number of false-negative diagnoses in the Non-Neoplastic category and the number of false-positive diagnoses in the Neoplastic categories while conveying a heightened degree of suspicion to clinicians and encouraging further work-up. The AUS category is heterogeneous, encompassing a range of non-neoplastic and neoplastic lesions, including cystic lesions and lymphoid-rich entities, resulting in morphological overlap between non-neoplastic and neoplastic processes. FNA specimens classified as AUS can be due to pre-analytical factors (e.g., FNA technique, inadequate sampling, smearing technique, air drying artifact, obscuring background) or the inherent characteristics of the lesion (e.g., cystic, fibrotic, necrotic) resulting in a limited number of well-preserved cells. The AUS category should be used rarely and judiciously. In retrospective studies, the proportion of FNAs diagnosed as AUS was approximately 4% with a wide range (0–73%), highlighting the vast differences in salivary gland FNA practices across different institutions. The reported risk of malignancy (ROM) and of neoplasia (RON) for the AUS category were also in a wide range, with an average ROM and RON of 30% and 63% for cases with surgical follow-up, respectively. A diagnosis of AUS warrants correlation with clinical and radiologic findings, as well as personalized management and risk assessment for each patient, resulting in clinical follow-up, repeat FNA, core-needle biopsy, open biopsy, or surgical excision.