Mitoses in Epithelial-Predominant Pleomorphic Adenoma
Mitoses are NOT commonly found in epithelial-predominant pleomorphic adenoma; when present, they are rare and should raise concern for atypical features or potential malignant transformation.
Key Histopathological Features
The available evidence consistently demonstrates that pleomorphic adenomas typically exhibit low mitotic activity:
- In a comprehensive multicentric study of 130 pleomorphic adenomas, increased mitotic activity was observed in only 5.4% of cases, making it a rare finding 1
- Another study examining fine needle aspiration cytology correlation with histopathology found no significant difference in mitotic figures between cytology and histology, but mitoses were not a prominent feature in either 2
- Crystalloids (3.1%), increased mitotic activity (5.4%), and vascular invasion (2.3%) were all rarely observed in the multicentric analysis 1
Clinical Significance of Mitotic Activity
When mitoses ARE present in pleomorphic adenoma, this finding carries important implications:
Atypical Features
Recent evidence indicates that pleomorphic adenomas with increased mitotic activity may represent atypical variants that require careful evaluation 3, 4. These cases may exhibit:
- Features of dysplasia without extra-capsular invasion
- Cellular pleomorphism
- Heightened proliferative activity (found in 93.3% of cases with pseudomalignant cytomorphology) 4
Distinction from Malignancy
The presence of mitoses should prompt consideration of:
- Carcinoma ex pleomorphic adenoma, which characteristically shows high mitotic activity along with cellular pleomorphism, perineural invasion, and vascular invasion 3
- In situ/intracapsular salivary duct carcinoma, though recent evidence suggests these intratumoral atypical lesions have good prognosis when confined within the adenoma borders 5
Practical Diagnostic Approach
For pathologists evaluating epithelial-predominant pleomorphic adenoma:
Document mitotic activity carefully - any increased mitotic figures warrant mention in the pathology report
Assess for associated features including:
Complete excision with negative margins is curative for cases with epithelial atypia confined within the tumor borders, even when mitoses are present 5
Common Pitfall
Do not overinterpret rare mitotic figures as evidence of malignancy if the tumor remains well-encapsulated without invasion. However, increased mitotic activity (>5% of cases) combined with other atypical features should prompt thorough sampling and careful margin assessment to exclude carcinoma ex pleomorphic adenoma 1, 3.