2009 Volume 21 Issue 4 Pages 269-275
Atypical pleomorphic adenoma (PA) is a premalignant condition of PA, although its immunoreactivity for HER2/neu, which is a marker for carcinoma (Ca) ex PA, is still unclear. We investigated the pathology and HER2/neu immunoreactivity of atypical PA, and compared the results with Ca ex PA and benign PA cases. The mean age of atypical PA was statistically lower and the size tended to be smaller than Ca ex PA. Pathologically, hypercellularity was observed in 10 cases of atypical PA, and 8 cases showed capsule violation. Immunohistochemically, the HER2/neu positive ratio in hypercellular foci of atypical PA was 40%, significantly higher than the ratio in benign PA, and significantly lower than that in Ca ex PA. However, the ratio in capsule violation foci of atypical PA was 0%, as in benign PA. Thus, hypercellularity was considered to indicate greater potential for malignant transformation than capsular violation. Further studies are needed to determine whether atypical PA with HER2/neu expression undergoes malignant transformation more frequently than HER2/neu-negative atypical PA.
