Basaloid follicular hamartoma
What is a basaloid follicular hamartoma?
Basaloid follicular hamartoma is a rare, harmless hair follicle tumour that occurs on the face and scalp, and occasionally, the trunk. It is characterised histologically by an overgrowth of branching cords and strands of basaloid cells. It is very important to distinguish basaloid follicular hamartoma lesions from skin cancer. This is done by careful histopathological examination of a skin biopsy (see below).
Basaloid follicular hamartoma is split into two categories:
Solitary/localised basaloid follicular hamartoma
Solitary basaloid follicular hamartomas are isolated lesions. They may be congenital (present from birth) or acquired (appear later).
Multiple basaloid follicular hamartoma
Multiple basaloid follicular hamartoma are subdivided into two categories:
- Familial multiple basaloid follicular hamartoma has autosomal dominant inheritance. Lesions occur diffusely on the face, trunk and extremities.
- Generalised basaloid follicular hamartoma syndrome is a subtype of hereditary multiple basaloid follicular hamartoma with additional cutaneous features, including milia, comedone-like lesions, hypotrichosis (reduced hair) and hypohidrosis (reduced sweating).
- Linear unilateral basaloid follicular hamartoma – lesions occur along the lines of Blaschko due to mosaicism.
- Generalised basaloid follicular hamartoma – may be associated with autoimmune disease (myasthenia gravis, systemic lupus erythematosus (SLE)), or sporadic (rare).
What does basaloid follicular hamartoma look like?
Solitary basaloid follicular hamartoma lesions occur most often on the face and scalp. They range in size from 1 mm to 3cm. They are skin-coloured to brown. Hair may be absent.
Multiple basaloid follicular hamartomas often start on the face and scalp but then spread to other areas including the neck, trunk and limbs. The number of lesions can range from a few to hundreds of papules. These are usually skin coloured and about 1-2 mm in size.
How is basaloid follicular hamartoma diagnosed?
Basaloid follicular hamartoma is diagnosed on full-thickness skin biopsy. Clinical features of basaloid follicular hamartoma can be very similar to those of other skin tumours such as basal cell carcinoma and trichoepithelioma, so resampling or re-excision may be necessary for definitive diagnosis or complete eradication in uncertain cases.
Basaloid follicular hamartoma has been linked to a mutation in the PTCH gene, which is part of the same pathway implicated in nevoid basal cell carcinoma syndrome (Gorlin syndrome). It is important to keep the patient under observation, as they may be at risk of skin cancer.
What is the treatment of basaloid follicular hamartoma?
Basaloid follicular hamartoma is a benign tumour that usually requires no treatment. Occasionally they may be surgically removed for cosmetic reasons or if they occur in functionally sensitive areas.
Patients with basaloid follicular hamartoma should be monitored and biopsy performed on lesions if they change in size or appearance. Any suspicious tumours should be removed using:
- curettage and electrodesiccation
- surgical excision.
- Mohs micrographic surgery, which ensures clear margins