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Program Number: B310
Session Name: Poster Session

Use of IHC in Diagnosis and Determination of Malignancy for FNA Cytopathology of Salivary Gland Lesions

Madison Thompson; Neema Rashidi; Angeline A Truong; Nina Patel, MD; Rohith Bhethanabotla; Sarah Honjo; Annemieke van Zante, MD, PhD; Vimal Krishnan, MD; Anastasiya Pigal, MD; Elham Khanafshar, MD, MS; Ron Balassanian, MD; Britt-Marie Ljung, MD; Mary J Xu, MD; Katherine C Wai, MD; Ivan H El-Sayed, MD; Jonathan R George, MD, MPH; Chase M Heaton, MD; William R Ryan, MD; Steven Long, MD; Patrick K Ha, MD; University of California San Francisco

Background: Fine-needle aspiration (FNA) allows for rapid and minimally invasive assessment of salivary gland lesions; however, definitive diagnosis can sometimes be elusive. Salivary gland lesions pose unique diagnostic challenges due to overlapping histology, as well as diversity in the cellular appearance of individual lesions. The focus of this paper is to determine whether immunohistochemistry (IHC) is effective in obtaining an accurate diagnosis and assessing for malignancy in FNA compared to the definitive surgical pathology. 

Methods: Salivary gland lesion cases from 2010-2023 were retrospectively identified, and clinical variables extracted including demographics, imaging, FNA cytopathology, surgical pathology, treatment, recurrence, and vital status. The study included cases of salivary gland lesions from a single tertiary care center that underwent FNA and surgery at the same anatomical site. IHC use was confirmed by reviewing FNA cytopathology reports.  Malignant cases diagnosed by FNA were identified, including cases where explicit concern for malignancy was described in the cytopathology report. 

Results: A total of 275 cases met the study’s inclusion criteria. Cases were comprised of benign salivary gland tumors or other benign pathology (175), malignant salivary gland tumors (60), metastatic cancers (34), and lymphomas (6). Overall, 73 FNA specimens received IHC testing and 202 did not.   

There were 37 cases with IHC and 65 cases without IHC in which the FNA histological final diagnosis did not exactly match the surgical pathology diagnosis. Among IHC cases, IHC was able to narrow the differential diagnosis in the FNA cytopathology report to include the final diagnosis 22/37 (59%) of cases. In cases without IHC, 29/65 (45%) of the FNA reports included the surgical pathology diagnosis in the differential. 

A total of 60/275 cases were determined to be malignant salivary gland tumors on surgical pathology. 32 of these specimens received IHC while 28 did not. 97% of cases with IHC were accurately identified as malignant while only 83% of cases without IHC were accurately identified as malignant in the FNA cytopathology report (p<0.05). 

Treatment plans varied between all cases that were suspected of malignancy and those that were diagnosed as benign on FNA cytopathology. Variation in time between initial FNA and surgery was observed between cases suspected of malignancy [M = 24.6 days, 95% CI (20.9, 28.3)] and those that were suspected to be benign [M = 66.8 days, 95% CI (56.0, 77.6)]. Additionally, among cases with suspected malignancy 44% (56/127) underwent neck dissection compared to only 11% (17/148) of cases that were suspected to be benign (p<0.001). 

Conclusions: IHC can be useful to narrow the differential diagnosis for FNA cytopathology of salivary gland lesions. The accuracy of FNA diagnosis of malignant salivary gland lesions can impact surgical management such as time from initial diagnosis to surgery and inclusion of neck dissection. Consideration should be given to the use of IHC when analyzing salivary gland lesions upon initial sampling to ensure accuracy in a diagnosis that will guide patient care. Further studies may investigate the cost benefit analysis of increasing the use of IHC for FNA of salivary gland lesions. 

 

 

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