Establishment of an efficient pathologic diagnostic platform using core needle biopsy for salivary gland carcinoma

Purpose: A major problem in establishing treatment strategies for salivary gland cancer is the difficulty of preoperative histologic typing. In recent years, genetic evaluation has become essential for salivary gland tumor diagnosis. The core needle biopsy (CNB) allows a small piece of the center of the tumor to be taken intact and analyzed in detail. The purpose of this study was to clarify the efficacy and the limitations of CNB in the preoperative diagnosis, and to establish a generalizable preoperative histologic typing platform. Methods: Paired preoperative 20-gauge core needle biopsy (CNB) and surgical specimens from 41 patients with malignant salivary gland tumors were reviewed. Morphological evaluation, immunohistochemical evaluation, and break-apart fluorescence in situ hybridization (FISH) assay were performed as histologic typing methods for CNB. The quality of biopsy specimens, diagnostic accuracy, and immunostaining concordance rates between biopsy and surgical specimens were analyzed. Results: For CNB, 95% (39/41) of the specimens were of high quality, allowing adequate morphologic, immunohistologic, and genomic analysis. Two patients had unanalyzable specimens due to cystic fluid or tumor firmness. Overall, 75% (31/41) had correct preoperative histologic typing. Compared to other histologic types, carcinoma ex pleomorphic adenoma (CXPA) and salivary duct carcinoma arising from CXPA had a significantly lower concordance rate for histologic typing (50% vs. 89.6%, p=0.016) and poorer HER2 immunostaining concordance rates between CNB and surgical specimens (60% vs. 0%, p=0.001). There were no recurrences due to tumor seeding after CNB. Conclusions: Detailed analysis of CNB specimens allows for highly accurate determination of salivary gland carcinoma histologic type with molecular diagnosis. However, careful histologic typing is necessary in pathologically heterogeneous tumors.