Acral Lentiginous Melanoma

 Rare to absent in early lesions, prominent and confluent in late lesions


image Nests are irregular in size and shape, randomly alternate with single melanocytes


• Cells show elongated, ovoid hyperchromatic nuclei with little cytoplasm

• Elongated, ovoid shape with little cytoplasm




Top Differential Diagnoses




• Acral melanocytic nevus
• Spindle cell melanoma

• Clinical differential

image Subungual hematoma caused by trauma (talon noir)

image Tinea nigra (darkly pigmented macule with irregular borders)


Diagnostic Checklist




• Early lesions are difficult to diagnose

• Very few neoplastic melanocytes may be present

• Exercise caution when evaluating partially sampled lesions

image
Acral Melanoma Presenting as Unevenly Pigmented Plaque
The heel of this patient shows a dark brown plaque with early depigmentation and an erythematous rim image. The lesion has a sharp border on the medial aspect image. (Courtesy J. Finch, MD.)


image
Early Lentiginous Growth in ALM
Lentiginous growth of atypical melanocytes image is seen in this early in situ lesion. Only rare upward scatter image of atypical melanocytes is identified. A Meissner corpuscle image is seen in the dermis. There is marked uneven melanin incontinence image.

image
Poorly Nested Pattern in ALM
There is a lentiginous growth image and poorly nested growth pattern image identified at the dermal-epidermal junction. There is only limited pagetoid upward scatter image, unlike cutaneous melanoma. The finding of lentiginous growth with cytological atypia is sufficient for the diagnosis of melanoma in situ, acrolentiginous type.

image
Angulated, Hyperchromatic Nuclei in ALM at High Magnification
Higher magnification of same lesion shows angulated, hyperchromatic nuclei with scant amounts of cytoplasm image. Note the melanocytic hyperplasia has replaced most of the basal keratinocytes.


TERMINOLOGY


Abbreviations




• Acral lentiginous melanoma (ALM)


Definitions




• Form of cutaneous melanoma that microscopically grows in lentiginous array and occurs on acral sites
image Palms and soles

image Digits and subungual regions


CLINICAL ISSUES


Presentation




• < 5% of all malignant melanomas
• More common on sole of foot or in subungual region of big toe or thumb

• Most frequently reported symptoms are change in size, bleeding, change in color, and becoming raised or nodular

image May remain flat or present as large, pigmented macule

image Lesion becomes darker and more irregular as it progresses

image Invasive areas may be associated with hyperkeratotic plaques, papules, nodules, and even ulceration

image Spreads rapidly

• Average age at diagnosis: 60-70 years

• Relatively uncommon in Caucasians, but most common subtype of melanomas in Asians and Africans


Treatment




• Surgical approaches
image Wide surgical excision and amputation give comparable survival rates

image In many cases of subungual melanomas, amputation is preferred due to relative lack of soft tissue between tumor and bone beneath nail


Prognosis




• Compared to other cutaneous melanomas, disease-specific survival rates are lower
image 5-year melanoma-specific survival rates: 80.3%

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Acral Lentiginous Melanoma
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