The final diagnosis of melanoma is made only after histological examination of the lesion. This usually involves an excisional biopsy through the entire thickness of the skin with a 1- to 3-mm margin of healthy tissue, which means that not only the lesion itself is removed, but also a small part of the surrounding skin. The technique of radical removal depends on the size of the tumour.
The histological examination assesses the architectural and structural features of the tumour and its constituent cells. Each type of melanoma has its own histological features. In difficult diagnostic cases or in the investigation of suspected melanoma metastases, immunohistochemical (i.e. cell marker) tests are performed. Molecular tests for common mutations (e.g. mutations in the BRAF gene) are also performed. This is important when planning treatment with systemic drugs.
Histological examination determines the type of melanoma, the thickness of the tumour, the extent of vascular spread, the margins of the incision (i.e. whether the tumour has been radically removed, whether there are no tumour cells in the margins of the incision), the phase of growth, signs of regression, the depth of invasion into the skin and other prognostic parameters.
The data obtained from this study not only confirms the final diagnosis but also helps to establish a plan for further treatment and follow-up of the patient.