How is melanoma diagnosed ?

The clinical examination and medical questioning

In cases of suspected melanoma, diagnosis confirmation will often be made by a dermatologist, a specialist in skin and skin-related diseases.

Before conducting a clinical examination, the dermatologist will ask the patient about observations made during self-monitoring, any symptoms experienced, and their current or past health issues (medical history). The dermatologist will look for risk factors for melanoma and will specifically inquire if close relatives have had melanoma.

The clinical examination will be thorough, covering the entire skin to check for any nevi or suspicious skin lesions. Diagnosis orientation will be guided by the "ABCDE" rule. To refine the diagnosis, the dermatologist may use a dermatoscope, an optical instrument that magnifies and allows better observation of the edges and color variations of a skin lesion.

During the clinical examination, the dermatologist will also examine various lymph node areas to check for lymph nodes that may have been invaded by cancer cells. They will pay particular attention to lymph nodes located in the groin (the area where the thighs meet the trunk), under the arms (the hollow area beneath the shoulder, at the junction of the arm and thorax), and above the clavicle (supraclavicular area).

Excision and histological analysis

In the presence of a suspicious lesion, a limited but complete excision will always be performed. The surgical specimen will be examined microscopically by a pathologist, a medical specialist in cells, tissues, and organs. The pathologist will confirm or rule out whether it is melanoma. They will also specify the characteristics of the cancerous cells (histology) and the type of melanoma.

Different types of melanomas

There are different types of melanomas, each requiring specific management, treatment, and follow-up.

Superficial spreading melanoma is the most common form, accounting for about 80% of diagnosed melanomas. It primarily affects younger adults. Intense, brief sun exposure is often involved. This type of melanoma is usually invasive, with a prolonged horizontal phase, lasting about 3 to 7 years, followed by a vertical phase.

Nodular Melanoma representing approximately 20% of diagnosed melanoma cases, it typically appears between the ages of 40 and 50. It affects both covered and uncovered areas of the skin and exhibits immediate vertical growth. This form is more aggressive.

Lentigo Maligna Melanoma arises from a pre-existing lentigo maligna. It accounts for about 10% of melanoma cases and primarily affects older individuals. The horizontal growth phase of these melanomas is very long, lasting from 10 to 20 years

The pathologist will determine the thickness of the lesion (Breslow index), the number of dividing cells (mitotic index), and the presence or absence of ulceration (skin alteration).

Histological grade

The anathomopathologist will also determine the histological grade of the tumor cells.

A portion of the surgical specimen will be sent to a molecular biology laboratory. Such a laboratory specializes in studying the DNA of tumor cells to look for mutations in certain genes. Biologists in this laboratory will specifically look for mutations in the BRAF, NRAS, and cKIT genes. Knowledge of any mutations will help in selecting medications that target a mutated gene (targeted therapies).

Complementary examinations

When a melanoma is diagnosed, series of additional tests (pre-therapeutic assessment) will be conducted. Depending on the progression of the disease, various medical imaging tests will be prescribed: ultrasound, CT scan, MRI (Magnetic Resonance Imaging), or PET (Positron Emission Tomography).

The examination of the surgical specimen and the various additional tests will help define the stage of the melanoma. Determining the stage of cancer is primarily of therapeutic interest, as knowing the stage will help establish the most appropriate treatment for the patient. It will also help predict the most likely progression of the disease (prognostic interest).

The stage of a melanoma

Stage 0 melanomas are those in which cancer cells are present only in the upper or outer layer of the skin (epidermis).

Stage 1 melanomas are tumors less than 2 mm thick.

Stage 2 melanomas are less than 4 mm thick, with or without ulceration.

Stage 3 melanomas are cancers that have spread to at least one lymph node near the primary site of the cancer.

Stage 4 melanomas are cancers that have metastasized to distant parts of the body, such as the lungs or liver (source: Canadian Cancer Society).