Basal cell carcinoma: histological classification and body-site distribution.

BACKGROUND: Basal cell carcinoma (BCC) is the most common cancer worldwide in white-skinned populations. Recent studies suggest that BCC is not a single entity and that different histological subtypes show different clinical behaviour and might have different aetiology.

OBJECTIVES: To provide information on the incidence of BCC by histopathological subtype and body site.

METHODS: A case series of BCC from a prospective population-based register study collecting information on all excised and histologically confirmed skin cancers in Townsville, north Australia between 1997 and 1999.

RESULTS: Age-standardized incidence rates for nodular BCC were 727.1 per 100 000 inhabitants per year for males and 411.8 for females, while rates for superficial BCC were 336.5 for males and 251.4 for females. Incidence rates for 'high risk' BCC were 261.3 for males, 146.5 for females with infiltrative, and 156.7 for males and 100.2 for females with micronodular types. Superficial BCC occurred at a younger age, particularly in female patients. For all histological subtypes and both genders relative tumour density was highest for the face, followed by the neck. An exception was superficial BCC in males, where the posterior trunk was second, followed by the neck.

CONCLUSIONS: The study found a higher rate of superficial BCC than previous studies from less sun-exposed countries, and a more equal distribution of superficial BCC on face, trunk and limbs. These results seem to blur the difference between intermittent and continuous sun exposure as the causative environmental agents. The clinical implications of 'high risk' BCC rates are discussed.