Lentigo Maligna: Definition, Diagnosis, Treatment, and Prognosis

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What is Lentigo Maligna?

Lentigo malinga (LM), also known as Hutchinson’s melanotic freckle, is a subtype of cancer that slowly grows in chronically sun damaged skin, especially in elderly patients (66 to 72 years). This melanoma commonly appears in the head and neck.

This cancer has an especially high mutation rate. The risk of LM evolving into its more aggressive form (lentigo maligna melanoma or LMM) increases with time going from 5% to up to 50%. Between the 2 of them they represent 4 to 15% of all melanomas. Making LM/LMM the third most common subtype of melanoma.

Over the years there was an increase of cases that were reported. Many explanations could be given from higher exposure to sun rays to an increase in skin cancer awareness.

Aside from UVR, X-ray radiation, estrogen/progesterone, and nonpermanent hair dyes have been suggested as risk factors. Also LM is more likely to occur in genetic conditions that predispose to sun activities, like oculocutaneous albinism, xeroderma pigmentosum, werner syndrome and porphyria cutanea tarda.

Lentigo Maligna: Diagnosis

LM/LMM appears on critically sun damaged skin, especially in the head and neck (78,3% of cases). It presents as a slowly growing isolated large pigmented macule or patch with irregular borders. Sometimes it might have a discontinuous appearance with ill-defined borders. LM, due to its in situ nature, is typically smooth and non palpable, if it becomes invasive though. It may have a dermal component.

This subtype of cancer might prove difficult to distinguish in its early phases from benign changes of chronic solar damage. Also, because of the slow growth of its border and sometimes being hypomelanotic, its diagnosis might be delayed. This gives lentigo maligna time to evolve into papules, nodules or thick plaques, becoming LMM and having risk of metastatic disease.

Lesions are usually asymptomatic, although advanced tumors may produce pain, burn, itching and bleeding.

Non-invasive Diagnosis techniques

  1. Wood’s lamp: it emits in a specific wavelength of UV light which is absorbed by the epidermal melanin making superficially pigmented lesions appear darker than the rest.
  2. Dermoscopy: consists of a handheld magnifier lens with a light source that can be polarized or non-polarized. This method is considered superior to the wood’s lamp. When doing a dermoscopy the doctor checks for several patterns indicatives of LM. such as brown or grey dots around follicular openings. Other indicatives are polygons/rhomboids/zig-zag patterns, asymmetric pigmented follicular openings, etc.
  3. Reflectance confocal microscopy (RCM): this tool uses near-infrared laser light to obtain quasi histological images. RCM improves diagnostic accuracy of multiple skin tumors and is good for monitoring since it allows visualization of small amounts of melanin which would be invisible to the eye or dermoscopy.

Histopathology

A skin biopsy might be done for a definitive diagnosis if a lesson is suggestive of LM/LMM. This could be performed according to its purpose (incisional or excisional) or according to the technique (shave, punch, ellipse). The choice will depend on the location, size, cosmesis, and physician preference. Excisional biopsy is the gold standard to diagnose melanoma. This is because incisional biopsy can underestimate the depth of the lesion due to sampling error.

Lentigo Maligna: Treatment

  • Surgical excision: this is a simple procedure and the treatment of choice for both LM and LMM consist of removing the macules. The margins for this surgery need to be higher than the margins in other surgical excision.
  • Conventional surgery.
  • Mohs micrographic surgery: it consists of the excision of a skin layer after layer followed by examination in a microscope to check for cancer cells until these show no sign of cancer. This treatment is a time-costing technique.

Non-surgical treatment: often the location (head and neck) and the advanced age of patients represents an obstacle to surgical treatment.

  • Cryotherapy: as melanocytes are destroyed in temperatures between -4ºC to -7ºC, this treatment proves to be effective with no recurrence or metastasis observed after 75 months.
  • Radiotherapy: it can be used as primary treatment or adjuvant when positive margins are found after surgery. It’s also supported as treatment for LM when complete surgical excision is not possible.
  • Photodynamic therapy (PDT): it is a two-stage treatment which combines light energy with a drug (photosensitizer). This treatment is designed to destroy cancerous and precancerous cells.

There are others non surgical treatments but the data is inconsistent or proven to be ineffective (ingenol mebutate, azelaic acid, intralesional interferon alpha, fluorouracil and retinoids).

LM/LMM patients need to be consistently checked for progression, recurrence or persistence so monitoring is of high importance. This could be assisted by dermoscopy or RCM to check for the changes in papules and nodes over a treated area to know if the treatment was successful.

Lentigo Maligna: Prognosis

LM, in itself, is not decremental to a person’s lifespan. Studies show that patients who are completely excised have a high disease-specific survival rate (almost a 100%) in 10 years.

Once the tumor becomes invasive, it is comparable to other melanomas. If it is metastatic the survival rates in 5 years can drop.

While the mortality of LM is low, morbidity can be developed due to the potential large area that can be involved in both head and neck. The need for extensive surgical excision and reconstruction also contributes to this factor.

As UVR damage is the leading cause of this type of cancer, sun protection is key to prevention. Patients should wear broad-spectrum sunscreen whenever they are outdoors and reapply every 2 hours or immediately after swimming.

It’s also advised to avoid the sun during peak hours (10 am to 3 pm). Wearing SPF clothing might also be advised. It’s important to note that sunscreen is not an alternative for clothing or shade. No sunscreen will provide a 100% protection.

It is recommended to have a high index of suspicion and to be clinically diligent. As this will lead to an early diagnosis that would lower the chances of mortality and morbidity.

It is advised to consult a dermatologist if you feel any change in a mole or patch.

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