Proliferating trichilemmal tumour:: p53 immunoreactivity in association with p27Kip1 over-expression indicates a low-grade carcinoma profile

Aims: Alterations of cell-cycle regulatory molecules in tumorigenesis may predict the biological behaviour of neoplasms and greatly contribute to their proper classification. Since the behaviour of proliferating trichilemmal tumour (PTT) is controversial, we decided to explore the possible significance of altered p53 and p27(Kip1) immunohistochemical expression patterns in PTT, Methods and results: We evaluated the percentage and distribution of positive tumour cells and compared the results with those obtained from usual trichilemmal cysts (TC) and squamous cell carcinomas with trichilemmal differentiation (SCCT), PTT showed p53 immunoreactivity (50.4 +/- 29.6. mean +/- standard deviation) that was not statistically different from that seen in SCCT (75.2 +/- 36.3), On the other hand, p53 immunostaining was virtually absent in TC cases (positivity for p53 was observed in only one instance in < 1% of cells), As for p27(Kip1), the mean percentage of positive cells in PTT (82.7 <plus/minus> 9.9) was slightly lower than in TC (90.6 +/- 4.6) but significantly higher than in SCCT (53.4 +/- 30), Conclusions: The similar p53 immunoreactivity in both PTT and SCCT favour the interpretation of the former as carcinoma, albeit one whose behaviour would be tempered by the well-known regulatory effect exerted by p27(Kip1), the cell cycle.