Large-cell acanthoma of the skin. A study by image analysis cytometry and immunohistochemistry.

Although large-cell acanthoma is a well-known clinicopathological entity, its biologic spectrum and nature are still subject to debate. We studied seven cases of large-cell acanthoma by image analysis cytometry for DNA content and by immunohistochemistry, using antibodies to proliferating cell nuclear antigen (PCNA)/cyclin. The data were compared with individual cases of seborrheic keratosis (SK), actinic keratosis (AK), and Bowen's disease (BD). The DNA distribution of large-cell acanthoma was variable. There were varying peaks at the DNA index values of 1 and 2 (diploid and tetraploid values), but all cases contained a significant aneuploid population between DNA index of 1 and 2. The mean DNA index was 1.44 (1.27-1.77); 1-20% of the cells exceeded 2, and 0-2% exceeded 3. The DNA index for lesions in the other differential diagnostic groups studied was as follows: SK, 1.0; AK, 1.4; BD, 1.8. The percentage of cells with positive nuclear staining for PCNA/cyclin was < 20% in all cases of large-cell acanthoma. The discrepancy between the high number of aneuploid and tetraploid cells observed on the DNA distribution curve and the lack of evidence for significant proliferation based on immunohistochemical stains suggest that these cells are resting cells with abnormal DNA clone. Although these results provide additional information about the biologic nature of large-cell acanthoma, they do not resolve the controversial nosologic status of lesions in this histologic group.