[1331] Clinicopathologic and Immunophenotypic Characterization of Six Dedifferentiated Acinic Cell Carcinomas

Jennifer N Stall, Jonathan B McHugh. University of Michigan, Ann Arbor, MI

Background: Dedifferentiated acinic cell carcinoma (ACC) is a rare variant composed of low-grade (LG) ACC and a high-grade (HG) dedifferentiated component, either poorly differentiated adenocarcinoma or undifferentiated carcinoma. Given its aggressive clinical course, dedifferentiated ACC is important for surgical pathologists to recognize. Since only twenty cases have been reported and characterized to date, our goal was to describe the clinical, morphologic and immunophenotypic spectrum of six new cases.
Design: An institutional review from 1990-2011 for dedifferentiated ACC and high-grade carcinoma, not otherwise specified (NOS) identified six total cases. Clinical information and tissue were available for six and five cases, respectively. We evaluated the histologic features as well as immunophenotype using antibodies to CAM5.2, actin (SMA), S100, p63, p53, Ki-67, cyclinD1, β-catenin, estrogen receptor (ER), Her-2/neu, and androgen receptor (AR). Five LG ACC were stained for comparison.
Results: Median age was 55.5 y (range 47-70 y), with equal sex predilection and all occurred in the parotid. Half involved the facial nerve at presentation. Most (5/6) patients received total parotidectomy and LN dissection with adjuvant therapy (4/6). Distant metastasis occurred in 3/5 and LN metastasis in 4/5 cases over a median of 12.5 m (range 9-24 m). 4/5 died with a median survival of 2.8 y (range 0.9 – 8.8 y) and one is alive with disease. All were composed of LG microcystic ACC and a HG component consisting of invasive lobules of undifferentiated cells. Cribriform growth was seen in 2/5 and glands in 3/5. All HG areas had cells with acinic differentiation and these were prominent in 4/5. Perineural invasion, high mitotic rate, atypical mitoses and comedonecrosis were each seen in 4/5 cases. Compared to the LG ACC, the dedifferentiated components showed decreased S100 dendritic cells and CAM5.2 staining with increased cyclinD1, p53 and Ki-67. All cases were positive for membranous β-catenin and all were negative for p63, S100, SMA, AR, ER and Her-2/neu.
Conclusions: Dedifferentiated ACC demonstrated an aggressive clinical course with frequent facial nerve involvement, metastases and death. No definitive immunophenotypic profile could be determined from this small cohort, but the increased cyclinD1, p53 and Ki-67 are consistent with a more aggressive neoplasm. Although some may resemble salivary duct carcinoma, the negative AR and Her-2/neu argue against this. Recognition of dedifferentiated ACC is important for surgical pathologists as more aggressive clinical management is warranted.
Category: Head & Neck

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 156, Tuesday Afternoon


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