Malignant proliferating trichilemmal tumours: an histopathological and immunohistochemical study of three cases with DNA ploidy and morphometric evaluation

Aims: Malignant proliferating trichilemmal tumours (MPTT) are rare neoplasm s capable of tissue invasion and metastasis, the diagnosis of which is base d essentially on histological features. In difficult cases, however, evalua tion of additional parameters may be needed to diagnose malignancy. Methods and results: We report three cases of MPTT in which, in addition to the histological features, we have determined the DNA ploidy, nuclear area and proliferative fraction. CD34 immunoreactivity has also been tested. Tw o cases were aneuploid, and one diploid with increased proliferating index. PCNA immunostaining labelled 40% and 80% of tumour cells in aneuploid tumo urs and 30% of the diploid neoplasm. Ln all cases, nuclear area was consist ent with large pleomorphic tumour cells. No CD34 immunostaining was detecte d. Conclusions: Aneuploidy is common in MPTT, particularly in tumours with a h igh proliferative fraction. Loss of CD34 immunoreactivity is an additional feature of potential, though limited, value. Therefore, evaluation of the D NA content, proliferation markers and CD34 immunostaining may be helpful in the diagnosis of MPTT.