Primary dermal melanoma: a West Australian cohort

Background: The objectives of this study were to identify a subgroup of patients with putative primary dermal melanoma after thorough multidisciplinary clinical and histological evaluation, and to describe the clinical, histological and selected molecular features of these lesions.

Methods: The records of the Western Australian Melanoma Advisory Service were searched for potential cases of primary dermal melanoma. The clinical and histological features were reviewed, immunohistochemical assessment was performed and clinical outcomes recorded.

Results: Eighteen cases of putative primary dermal melanoma with available clinical data were identified. Two of 12 cases in which further histological sections could be obtained were excluded because of the presence of findings suggesting an epidermal origin on these further sections. In one additional case, such origin could not be histologically excluded. Median follow-up period for the remaining cases was 68 months. Confirmed primary dermal melanoma accounts for 0.87% of cases of melanoma referred to a subspecialist melanoma advisory service. These cases show significant histological overlap with dermal/subcutaneous metastases of melanoma, but display a relatively good prognosis, with a 5-year survival of 87.5%.

Conclusion: Our results support the recognition of a distinct group of melanoma that mimics metastatic melanoma, but is associated with a relatively favourable outcome. The group of putative primary dermal melanoma is likely to be heterogenous, including cases of primary nodular melanoma in which epidermal connection has not been identified, metastatic melanoma with an occult primary lesion and true primary dermal melanoma.