Basal cell naevus syndrome
What is basal cell naevus syndrome?
Basal cell naevus syndrome is a rare inherited condition characterised by:
- Multiple and early onset basal cell carcinomas
- Other tumours including melanoma, medulloblastoma, meningioma, breast carcinoma, non-Hodgkin's lymphoma, and ovarian fibroma
Synonyms for basal cell naevus syndrome (BCNS) include basal cell carcinoma nevus syndrome (BCCNS), Gorlin-Goltz syndrome, Gorlin syndrome, and nevoid basal cell carcinoma syndrome. The so-called basal cell naevi are actually tiny basal cell carcinomas.
Developmental abnormalities in affected individuals may include:
- Odontogenic cysts in the jaw
- Broad forehead
- Pits on palms and soles
- Rib anomalies
- Calcified falx cerebri (noted on skull X-ray)
Basal cell naevus syndrome
What is the cause of basal cell naevus syndrome?
Basal cell naevus syndrome is most often due to an abnormal PTCH 1 (patched) gene on chromosome 9q22.3-q31. This gene normally functions as a tumour suppressor so when it is not working properly it may allow cancers to grow. Other cases are due to mutations in 1p34.1 (PTCH 2 gene) or 10q24.32 (SUFU gene).
Basal cell naevus syndrome is an autosomal dominant condition meaning half of an affected person's children also have the syndrome. It affects one in every 50 to 100,000 people.
Recent research is studying how the genetics of basal cell carcinoma may lead to effective treatments in the future.
How is the diagnosis made?
A diagnosis of basal cell naevus syndrome can be made if there are 2 major or 1 major and 2 minor criteria.
- Multiple (>2) basal cell carcinomas at any age or one basal cell carcinoma less than 20 years or >10 basal cell naevi
- Histologically proven odontogenic keratocyst or a polyostotic bone cyst
- Palmar or plantar pits (3 or more)
- Ectopic calcification: lamellar or early (<20 years) calcification of the falx cerebri
- Family history of Basal cell naevus syndrome
- Congenital skeletal defects: bifid, fused, splayed, or missing rib, or bifid, wedged, or fused vertebra
- Large head with occipitofrontal circumference >97th percentile, with frontal bossing
- Cardiac or ovarian fibroma (benign tumour in heart or ovary)
- Medulloblastoma (a malignant brain tumour that usually arises in young children); this is usually associated with SUFU gene mutations
- Lymphomesenteric cysts (abdominal cysts full of lymph fluid)
- Congenital malformation: cleft lip and/or palate, polydactyly (extra fingers or toes), congenital eye defect such as cataract, microphthalmos (small eye) or coloboma (iris tumour)
Basaloid follicular hamartoma has also been linked to a mutation in the patched gene but is a benign tumour. There are solitary and multiple hereditary variants.
What is the treatment for basal cell naevus syndrome?
The first sign of basal cell naevus syndrome may be the development of a medulloblastoma in a child aged 2 to 5 years, but luckily this is uncommon. Only a few children with medulloblastoma also have basal cell naevus syndrome. If detected early enough, the tumour may be treated by surgery and chemotherapy.
Patients with basal cell naevus syndrome often require surgery to remove jaw cysts in their 20s. Often, it is not until they are in their 30s or 40s that the basal cell carcinomas begin to appear so the diagnosis of the syndrome is often delayed.
All patients with basal cell naevus syndrome should see a dermatologist for regular skin examinations so that basal cell carcinomas can be treated when they are small. This may require surgery or one of the many other treatments available for these tumours including cryotherapy, photodynamic therapy, fluorouracil cream and imiquimod cream. They should not receive treatment with irradiation as this is liable to provoke the development of more tumours.
Sun protection is vital to reduce the number of skin cancers developing but even complete protection will not prevent all basal cell carcinomas in patients with basal cell naevus syndrome.