Lentigo maligna is a form of melanoma in situ, representing the precursor to lentigo maligna melanoma, a malignant subtype of melanoma. This condition typically originates as a flat, asymmetrical, and irregularly bordered pigmented patch on the skin, often ranging in color from brown to tan. Over time, lentigo maligna can exhibit variegation in color, with some areas darkening unevenly, which can result in the gradual progression of the lesion going unnoticed. As the tumor grows, it may spread locally within the epidermis (the topmost layer of the skin), and if the malignant cells invade deeper into the dermis or subcutaneous tissue, the condition progresses to lentigo maligna melanoma. At this point, the lesion may become nodular or elevated, indicating a more aggressive and invasive form of melanoma.

 

Epidemiology and Pathogenesis

Lentigo maligna is more commonly seen in elderly individuals with a history of prolonged, cumulative sun exposure, particularly on areas such as the face, ears, and forearms, which are frequently exposed to ultraviolet (UV) radiation. The primary risk factor for lentigo maligna is UV-induced damage, which leads to the accumulation of genetic mutations in melanocytes, the cells responsible for producing melanin. These mutations, particularly in genes such as BRAF, contribute to the uncontrolled proliferation of melanocytes, eventually leading to the formation of the lentigo maligna lesion. Given the slow, indolent growth pattern of lentigo maligna, its early stages may not be readily apparent to patients, who may confuse the lesion with benign skin conditions such as solar lentigines, seborrheic keratoses, or benign moles.

 

Diagnosis

Diagnosing lentigo maligna involves a clinical examination, where dermatologists carefully assess the lesion’s size, shape, color, and borders. Due to its resemblance to benign conditions, lentigo maligna may require biopsy for definitive diagnosis. The biopsy typically reveals the presence of atypical melanocytes confined to the epidermis (in lentigo maligna), or if the lesion has progressed, it will show evidence of malignant cells extending into the dermis (in lentigo maligna melanoma) . Dermoscopy, a non-invasive imaging technique, can assist in differentiating lentigo maligna from other pigmented lesions by identifying characteristic patterns, such as irregular pigmentation and vessel formation within the lesion.

 

 

Treatment

The treatment of lentigo maligna depends on whether it remains confined to the epidermis or has progressed to lentigo maligna melanoma. The mainstay of treatment for lentigo maligna is local excision with clear margins, typically around 5mm of healthy tissue surrounding the lesion. This ensures complete removal of the malignant cells and reduces the risk of recurrence. In cases where the margins are not well-defined or if the lesion is located in a cosmetically sensitive area, more advanced techniques, such as Mohs micrographic surgery, may be employed. Mohs surgery involves the step-by-step removal of tissue, allowing for the precise excision of cancerous cells while minimizing damage to surrounding healthy tissue.

For lesions in difficult-to-reach areas, or for patients who are not candidates for surgery, alternative treatments may be considered, including:

  • Radiation Therapy: This can be used to treat lentigo maligna when surgical excision is not feasible due to location or patient condition. Radiation therapy targets and destroys cancer cells while sparing the surrounding tissue.

  • Cryotherapy: Cryosurgery, involving the freezing of the lesion using liquid nitrogen, can be used for superficial lesions but may be less effective for larger or deeper lentigo maligna lesions.

  • Topical Imiquimod: This immune-modulating cream has been shown to induce an immune response that may aid in the treatment of lentigo maligna. It is typically used in less invasive cases or as an adjunct to surgical methods.

If a biopsy confirms the progression of lentigo maligna to lentigo maligna melanoma, treatment protocols align with those for other types of malignant melanoma. This typically involves wider surgical excision and, in some cases, sentinel lymph node biopsy to assess for metastatic spread. Adjuvant therapies, including immunotherapy (e.g., checkpoint inhibitors like pembrolizumab) or targeted therapies (e.g., BRAF inhibitors), may be indicated depending on the stage and characteristics of the melanoma.

 

Prevention and Surveillance

Because the primary risk factor for lentigo maligna is UV exposure, preventive measures are paramount. These include rigorous sun protection strategies such as using broad-spectrum sunscreens with high SPF, wearing protective clothing, and avoiding sun exposure during peak hours (10 AM to 4 PM). Additionally, individuals at high risk for lentigo maligna, such as those with fair skin or a history of sunburns, should engage in regular dermatologic surveillance for early detection of suspicious lesions.

 

 

Conclusion

Lentigo maligna, although typically non-invasive when confined to the epidermis, can progress to lentigo maligna melanoma if left untreated. Early detection and intervention are crucial to prevent malignant transformation and the spread of cancer cells. Treatment options for lentigo maligna include excision, Mohs surgery, radiation therapy, cryotherapy, and imiquimod, depending on the location, size, and patient factors. With effective treatment and preventive measures, the prognosis for lentigo maligna is generally favorable, although surveillance remains important to monitor for any recurrence or malignant transformation.

 

References

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