High-grade transformation in acinic cell carcinoma of the salivary glands: A rare but important clinical entity.

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5581 Background: The phenomenon of high-grade transformation (HGT) has been described in select salivary gland malignancies. Previous studies of salivary gland HGT have noted a propensity for recurrent disease, lymph node (LN) metastases, and poor overall survival (OS). We report the clinical and pathologic findings in cases of acinic cell carcinoma (AcCC) with HGT (AcCC-HGT). Methods: A retrospective clinical and histopathologic review was performed on 62 patients (pts) with AcCC who had surgery at the Mayo Clinic from 1985-2010. Microscopic review was performed by two pathologists (JJG, WS). Cases of AcCC-HGT were characterized by cytomorphologic pleomorphism, elevated mitotic activity, infiltrative growth pattern, stromal desmoplasia, and necrosis. Immunohistochemical and histochemical stains were performed on cases of AcCC-HGT (AE1/AE3, Cam 5.2, p63, S100, Mib-1, PAS, and PAS-D). Results: AcCC-HGT was seen in 7 of 62 pts (11%). The median age was 53.5 years (range 15-84, 31 female) for pts with AcCC versus 69 years (range 56-68, 5 female) for pts with AcCC-HGT. Histologically, an abrupt transition from a low- or intermediate-grade component into a discrete high-grade component was typically seen. The areas of HGT exhibited elevated proliferation based on MIB-1 expression and significant loss of zymogen granules using PAS and PAS-D staining. Initial treatment for all pts was surgery; 7 AcCC and 3 AcCC-HGT pts also had adjuvant radiation. LNs were positive in 8% of AcCC pts (4/52, 3 unknown) at initial surgery compared with 43% of pts with AcCC-HGT (3/7). Known distant metastases developed in 2% of pts with AcCC (1/55) and 71% of pts with AcCC-HGT (5/7). Five-year recurrence free survival (RFS) was 82.7% for pts with AcCC and 19.0% for pts with AcCC-HGT (p<0.0001). Five-year OS was 93.5% for pts with AcCC and 40% for pts with AcCC-HGT (p<0.0001). Adjusting for age and gender, the hazard ratios for RFS and OS for pts with AcCC-HGT were 13.4 (95% CI, 3.6-50.1, p=0.0001) and 8.8 (95% CI, 2.1-35.5, p=0.0022). Conclusions: AcCC-HGT is a rare and aggressive salivary gland malignancy. The presence of HGT should be considered when determining indications for neck dissection, chemotherapy, and radiation.