Lentigo maligna melanoma is the first presentation of melanoma in which the cancerous cells are limited to the tissue of origin, the epidermis. Therefore, it is often reported as "in situ’" melanoma. It occurs in the sun-damaged skin and mostly on the neck or face, especially around the cheeks and nose. Lentigo maligna melanoma grows from a few millimeters to centimeters within 5 to 20 years or sometimes even longer. As a palpable lesion, the pigment of lentigo maligna melanoma is usually dark brown and a few millimeters large. It is the slowest growing and the least common type of melanoma. Although it is a slow-growing malignancy, the downside is that lentigo maligna melanoma can merge with other tumors like melanocytic nevus when developing. If detected early and treated, the prognosis is very good.
About 10% to15% of lentigo maligna melanoma patients have a family member with the disease. First-degree relatives have 8 to 12-times the risk of having lentigo maligna melanoma than individuals who do not have a familial history of LMM. Organ transplant and pills that weakens the immune system of an individual can also cause the formation of the cancerous cells. Undue exposure to ultraviolet radiation and a history of severe sunburn can also provoke the development of lentigo maligna melanoma, especially in adolescents and adults. A skin disorder called dysplastic nevus syndrome is also known to increase the risks of lentigo maligna melanoma. Xeroderma pigmentosum, a defect in the protein responsible for the repair of the DNA damaged by ultra-violet rays has also been discovered to be an underlying cause of lentigo maligna melanoma.
The incidence of lentigo maligna is highest in Hawaii and Australia with males being affected more often than females. Majority of the patients with the disease are older than 40 years, and the peak age of diagnosis is between 60 and 80 years. A study reported a 52% increase in the occurrence of lentigo maligna melanoma among people of age within 45 to 64 within 1990 and 2000 in the United States. The risk of the formation of the tumors is higher in fair-skinned people with a history of melanoma skin cancer and markers of actinic skin damage (solar lentigines and actinic keratoses).
Lentigo maligna is the preinvasive form of melanoma while lentigo maligna melanoma occurs when atypical melanocytes invade the dermal layer of the skin, thereby making the cancerous cells prone to metastasis. Prolonged damage to the skin causes it as a result of cumulative exposure to ultraviolet rays.
Microscopic examination is of great importance, especially for the diagnosis of lentigo maligna melanoma. It considers the features of the specimen obtained via biopsy in terms of invasion, differentiation, and depth. Note that, biopsy specimens usually include samples of the normal tissue, which would be used in spotting the differences. Also, there is the need for a full thickness biopsy to determine the depth of lesion and invasion levels correctly. Histopathological sections show contiguous growth of atypical melanocytes in the basal layer, individually and in nests. Melanocytes may be spindled, pleomorphic and may have a cytoplasmic retraction. Solar elastosis is prominent in the dermis. Epidermal atrophy, actinic damage, and basilar keratinocyte hyperpigmentation are usually observed.
Lentigo maligna melanoma manifests as an irregular patch of discolored skin. Initially, it often resembles brown marks (lentigines) or common freckles, but along the line, it becomes more noticeable and begins to expand across the skin. Like other forms of melanoma, it can be understood by the ABCDE rule of malignancy: asymmetry, border irregularity, color variation, large diameter, and evolving of a mole.
It is not possible to diagnose lentigo maligna melanoma with the naked eye. Patients most often come to the hospital with complaints of a large diameter irregular lesion or nodule on their skin. Melanoma patients need a thorough and complete physical examination, with particular attention to the lymph nodes and skin. Hence, an excisional biopsy should be conducted to diagnose lentigo maligna melanoma.
Accurate diagnosis of lentigo maligna melanoma is critical. Clinical investigation is aided by dermoscopy and in some centers, by confocal microscopy. Dermoscopy helps in differentiating lentigo maligna from other skin lesions while confocal fluorescence microscopy is used to view the lesion in 3 dimensions. New techniques are being tested and evaluated to help classify the extent of lentigo maligna melanoma before excision biopsy. The gold standard for diagnosing lentigo maligna melanoma is a full-thickness skin biopsy and dermatopathological analysis of the biopsy specimen. Other tests are not mandatory in the majority of cases, but those with invasive melanoma deeper than 1-mm thick should have imaging studies and a lymph node biopsy as part of their workup.
The standard and most preferred treatment for lentigo maligna melanoma is surgical excision. However, for patients who cannot have surgery, several conservative therapies can be applied. These therapies include cryotherapy, chemotherapy, and immune therapy with topical imiquimod. Occasionally radiotherapy is applied to destroy melanoma cells, though studies have shown mixed feelings concerning the effectiveness of this therapy option because it may miss focal lentigo maligna melanoma. Non-surgical therapies have been documented to have a recurrence rate of 20% to 100% in 5 years. This shows that surgical resection is the best treatment modality.
Separating lentigo maligna melanoma from its predecessor remains a diagnostic dilemma especially in cases with cryotherapy and other therapeutic interventions. It is important to use a low threshold for biopsy of pigmented facial tumors. More than 50% in a series of 85 excised lesions with a clinical diagnosis of lentigo maligna melanoma were reported to have lentigo maligna melanoma.
Consideration should be given to the following conditions when patients are evaluated for suspected lentigo maligna melanoma and lentigo maligna:
The treatment depends on the thickness of the invasive component of the lentigo maligna, and it is similar to other melanomas of the same thickness and stage.
Lentigo maligna melanoma is staged to determine the degree of severity, presence or absence of metastasis and to prescribe the best treatment plan.
The prognosis of lentigo maligna melanoma is fair unless it has metastasized (spread). A patient’s prognosis depends significantly on the time, overall wellness of the patient, diagnosis, and depth of the lesion.
Potential pitfalls that have been linked to lentigo maligna melanoma include late diagnosis or inadequate follow-up care. In most cases, doctors fail to diagnose lentigo maligna and brush it off as a benign skin lesion.