Dermoscopy of melanoma

Phases and types of tumoral growth

Melanoma's growth may either be biphasic or monophasic.

The biphasic model consists of an initial radial or horizontal growth, followed by a phase of vertical development, which corrisponds to the dermal and hypodermal infiltration.

A melanoma which develops in a biphasic fashion is the superficial type; the so called “lentigo maligna melanoma”. Often, even acral lentiginous melanomas follow a biphasic growth.

The monophasic growth type consists in an exclusive vertical diffusion and this formation is called nodular melanoma.

Melanomas are conventionally classified on the basis of their growing type.

They can be divided in four major types: superficial spreading melanoma (65%), nodular melanoma (25%), and acral lentiginous melanoma (5%).

Superficial spreading melanoma, lentigo maligna and lentiginous melanoma are classified as radially growing tumors, while noduar melanoma is a vertical growing tumor.

Other types of vertical growing tumors are represented by desmoplastic and minimal deviation melanoma.

Superficial melanoma comprises two thirds of total malignant melanomas. It is usually asymptomatic and ofted diagnosed when it's smaller in size than lentigo maligna. It mostly affects legs in women and the back in men. This type of melanoma is usually a plaque lesion, with irregular borders, presence of brown infiltrates which often show small eritematous whitish, black or blue spots and blue and black nodules. Small notches can be found at margins toghether with  changes in the pigmentation pattern. The histologic exam frequently reveals the existence of atypical melanocytes invading the derm and hypoderm.

Nodular melanoma comprises the 10-15% of all malignant melanomas. It affects every part of the body and manifests itself under the form of a prominent dark, white pearl or grey papule. Occasionally the lesion may contain small amounts of pigment and may can misdiagnosed with a vascular neoplasy. Until an ulcer forms, nodular melanomas are asymptomatic.

Lentigo maligna melanoma originates from lentigo maligna (pre-maligna Hutchinson lentigo or malignant in situ melanoma). This lesion tipically localizes on the face and on other sun-exposed body surfaces of elderly patients, who present irregularly shaped brown maculae, 2-6 cm in diameter, covered with brown or black irregularly diffused patches.

In Hutchinson lentigo, both malignant and benign melanocytes remain confined to the epidermis; when melanocytes invade the derm, the lesion is called lentigo maligna melanoma and may metastize.

Acral lentiginous melanoma, although being rare, is the most frequent form of melanoma affecting dark skinned individuals. It evolves on palmar-plantar and subungueal surfaces and shows characteristic histological features similar to those found in lentigo maligna melanoma.

Malignant melanomas can also be found on oral mucoasae, in the genital region and in the conjunctive. Melanoma of mucosae (anal-rectal region) are mostly found in white people and has a poor prognosis.

The term melanoma in situ refers to the stadium in which the neoplasy is localized in the epidermis, in the epitelium of the hair follicle or in the excretory ducts of sweat glands.

Since this neoformation occupies a position far from the vascular plexus and because of the absence of malignant melanocytes in the derm, the melanoma in situ rarely metastizes.

Clark and Breslow's melanoma staging

Once someone is diagnosed with melanoma, it is important to determine how deep the melanoma has invaded the dermis and if it has spread to lymph nodes. To test this possibility, the physician may order a variety of blood tests, X-rays, scans and other special tests. This process is called 'staging'.

The specific treatment of a melanoma is based on the stage of trhe tumor at the time of the diagnosis.

The first step in staging a melanoma consists in its surgical excision and histological examination. The pathologist determines how deep into the skin layers the melanoma has grown.

Wallace Clark, Jr. , M.D., University of Pennsylvania Medical School, developed a still accepted classification method for melanomas based on the grotwh type.

When a melanoma has grown into the deeper layers of the skin, there is a higher risk that it might spread to other areas of the body.

Another method for determining how deeply melanoma has invaded is to measure the depth.

A direct measurement of the depth is often called Breslow's Staging.

Both Clark's and Breslow's staging can provide reliable information on the risk of tumor's spreading. The important feature is that the risk of death from melanoma increases as the depth of the melanoma is highe.

If the melanoma has not spread beyond where it started, it is considered 'local' and is generally treated by surgerical intervention. If the melanoma has gained access to the lymphatic system and has spread to the local lymph nodes, it is considered regional. Finally, if the melanoma spreads beyond the local lymph nodes, it is considered metastatic.

After Clark's Level and Breslow's staging have been determined, the physician will 'stage' the melanoma on the basis of the results obtained from  other performed tests (X-rays, scans, blood tests). 'Staging a tumor' is an important process since the treatment will be based on the stage of the melanoma.

In situ and early invasive melanoma are generally macular lesions with a small diameter, slighty palpable, with an asymmetrical shape and irregular borders, and a pigmentation which varies from red to brown and black. The differential diagnosis with Clark naevus may be quite challenging even for trained dermatologists.

Invasive melanoma usually presents itself as a papular or nodular formation, sometimes ulcerated and typically with differents tones of pigmentation, ranging from brown to black or even red-whitish and blue areas. Sometimes pigmentation is not present and the lesion is the so called amelanotyc melanoma.

Recently Wolf et al. Demonstred that the diagnostic performance of the physician in cases of thick melanomas (Breslow index >4mm) may be less accurate than in the case of in situ melanomas.

The anamnestetic reporting modifications in size, shape and color of the lesions, may result of great utility in the diagnosis of melanoma when ulceration and spontaneous bleeding are observed.