Malignant proliferating trichilemmal tumours: an histopathological and immunohistochemical study of three cases with...

Malignant proliferating trichilemmal tumours (MPTT) are rare neoplasms capable of tissue invasion and metastasis, the diagnosis of which is based essentially on histological features. In difficult cases, however, evaluation of additional parameters may be needed to diagnose malignancy.

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. Two cases were aneuploid, and one diploid with increased proliferating index. PCNA immunostaining labelled 40% and 80% of tumour cells in aneuploid tumours and 30% of the diploid neoplasm. In all cases, nuclear area was consistent with large pleomorphic tumour cells. No CD34 immunostaining was detected.

Aneuploidy is common in MPTT, particularly in tumours with a high proliferative fraction. Loss of CD34 immunoreactivity is an additional feature of potential, though limited, value. Therefore, evaluation of the DNA content, proliferation markers and CD34 immunostaining may be helpful in the diagnosis of MPTT.