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Pathology of Acral Lentiginous Melanoma

Dr Sampurna Roy MD          

 

                                                                                                                      

 

The term Acral lentiginous melanoma was first described by Reed as a variant of melanoma .

Acral lentiginous melanoma (ALM) is the fourth distinct variant of cutaneous melanoma.

It was so named due to its predilection of acral areas of the body (palmar, plantar and subungual skin) and its prominent radial or "lentiginous" growth pattern.

Although ALM is the rarest subtype of cutaneous melanoma, it represents the most common category diagnosed on the foot.

It is the most common type of malignant melanoma in Asians, African and North American Blacks, but is relatively infrequent in Caucasians.

It occurs predominantly in the sixth, seventh, and eighth decades of life, with a peak incidence in the seventh decade for males and in the sixth decade for females.

Macroscopically, the lesion presents as  pigmented and ulcerated plaques or nodules. 

Microscopic features:

      

Histologically, the tumour has a radial growth phase and is characterized by lentiginous and some nesting proliferation of large atypical melanocytes. 

Focally, pagetoid spread is present, however this is not as prominent as in superficial spreading melanoma.

The melanocytes may be surrounded by a halo giving a lacunar appearance.

Some of the melanocytes may have dendritic processes.

The invasive dermal component may be composed of spindle or epithelioid  cells or nevus like cells.  

Diagnosis of Acral lentiginous melanoma during the radial growth phase is often difficult, and it may not be recognized initially, but treatment in this phase offers an excellent prognosis.

There is a high incidence of regressive changes and desmoplasia in Acral lentiginous melanoma.

These changes, together with the anatomic peculiarities of nail beds, palms, and soles as compared with other skin areas, make it difficult to determine the Clark's level and to measure the depth of invasion.

 

Treatment:

(i) Melanomas less than 1.00 mm deep and those in the radial growth phase with minimal invasion require only wide local excision.

(ii) Wide local excision with lymph node dissection is recommended for subungual melanomas measuring more than 1.00 mm and for lesions showing severe regression. 

(iii) Amputation of digits and lymph node dissection are recommended for subungual melanomas, if the melanomas exhibit the vertical growth phase.

(iv) If there is only radial growth without regressive changes, wide local excision is adequate.

 

Further reading:

Acral lentiginous melanoma in situ: a study of nine cases.

Acral lentiginous melanoma: an immunohistochemical study of 20 cases.

Acral cutaneous melanoma in caucasians: clinical features, histopathology and prognosis in 112 patients.

Acral lentiginous melanoma (including in situ melanoma) arising in association with naevocellular naevi.

Acral lentiginous melanoma. A histological type without prognostic significance.

Acral lentiginous melanoma.

Acral lentiginous melanoma. A clinicopathologic study of 36 patients.

Histological type and biological behavior of primary cutaneous malignant melanoma. 2. An analysis of 86 cases located on so-called acral regions as plantar, palmar, and sub-/parungual areas.

Acral lentiginous melanoma. A clinicopathologic entity.

 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)

 

 


 

 

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