Trichoblastic carcinoma is a rare hair follicle tumour that is thought to occur from a malignant transformation of a benign trichoblastoma. The tumour arises from follicular germinative cells and develops dermal or subcutaneous fat invasion. In the very few reported cases of trichoblastic carcinoma, the primary trichoblastoma lesion had been a painless mass slowly growing over a period of years. In one case, the tumour had been present and unchanged for as long as 40 years but then suddenly grew bigger, became inflamed and painful.
Lesions of trichoblastoma are often found on the face and scalp of adults around 40-50 years of age. If the trichoblastoma has been left untreated, it can undergo malignant transformation into a trichoblastic carcinoma. In some cases, where the original trichoblastoma has been excised, a recurring lesion with high metastatic potential may develop at the same site years later.
Trichoblastic carcinoma tumours have also occurred on other parts of the body including the forearm, lower back and thigh. They have been found in both male and female patients aged between 40-90 years of age. Some patients may experience occasional moderate itching and bleeding of the tumour. Tumours may be locally aggressive and lead to widespread metastases in the lymphatic and blood systems. Although rare, there have been several cases of trichoblastic carcinoma with widespread metastases and death.
Skin biopsy is the only definitive diagnosis for trichoblastic carcinoma. Ideally, the entire tumour should be excised and submitted for histological examination. The histology of trichoblastic carcinoma will differentiate it from other skin tumours that have similar clinical presentations, these include its benign counterpart trichoblastoma, trichilemmal carcinoma, pilomatrix carcinoma and basal cell carcinoma.
Histological findings of trichoblastic carcinoma are very similar to those found in basal cell carcinoma. It is extremely important to make the correct diagnosis, as basal cell carcinoma rarely metastasise and become life-threatening, whilst trichoblastic carcinoma can be aggressive and cause death.
Complete surgical excision with a margin of normal tissue is the recommended treatment. Mohs micrographic surgery may be used to ensure better margin control. Currently there is no consensus regarding the margin size of normal tissue. Additional radiotherapy and/or chemotherapy may be used to treat metastases and for locally aggressive tumours.
Prognosis in patients with trichoblastic carcinoma can be poor, especially if initially benign trichoblastoma lesions have been present for a long time and if patients are immunocompromised.
