High-grade transformation of acinic cell carcinoma: an inadequately treated entity?

OBJECTIVE: Acinic cell carcinoma (AcCC) is an uncommon salivary gland malignancy. We aim to characterize the clinical and pathologic characteristics of AcCC with and without high-grade transformation (HGT). Importantly, cases of mammary analogue secretory carcinoma, a recently described histologic mimic of AcCC, have been excluded by using cytogenetics and molecular studies.

STUDY DESIGN: Archival surgical pathology material was obtained for patients diagnosed with AcCC at Mayo Clinic Rochester between 1990 and 2010. Tumors harboring the ETV6-NTRK3 fusion transcript were excluded from analysis by using cytogenetics and molecular studies. Tumors with HGT were characterized by areas with an infiltrative growth pattern, nuclear anaplasia, prominent nucleoli, brisk mitotic activity, geographic necrosis, and stromal desmoplasia. Demographic and clinical data were extracted from the medical records.

RESULTS: AcCC with HGT was seen in 8 of 48 cases (17%). Patients with AcCC with HGT were significantly older than patients without HGT (median 69 vs 54 years; P = .04). Angiolymphatic invasion was more common in AcCC with HGT (P = .02). Relapse-free survival and overall survival were significantly worse for cases of AcCC with HGT (hazard ratio 10.4 and 9.3, respectively; P < .0001 for both comparisons). Locoregional recurrence-free survival was not significantly different (P = .12), but distant metastases-free survival was significantly worse in patients with HGT compared with non-HGT patients (P < .0001).

CONCLUSIONS: Prognosis for overall survival and distant relapse for AcCC patients with HGT is significantly worse than that for patients without HGT.