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Acral Lentiginous Melanoma
Rare to absent in early lesions, prominent and confluent in late lesions
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
Subungual hematoma caused by trauma (talon noir)
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
Acral Melanoma Presenting as Unevenly Pigmented PlaqueThe heel of this patient shows a dark brown plaque with early depigmentation and an erythematous rim . The lesion has a sharp border on the medial aspect . (Courtesy J. Finch, MD.)
Early Lentiginous Growth in ALMLentiginous growth of atypical melanocytes is seen in this early in situ lesion. Only rare upward scatter of atypical melanocytes is identified. A Meissner corpuscle is seen in the dermis. There is marked uneven melanin incontinence .
Poorly Nested Pattern in ALMThere is a lentiginous growth and poorly nested growth pattern identified at the dermal-epidermal junction. There is only limited pagetoid upward scatter , unlike cutaneous melanoma. The finding of lentiginous growth with cytological atypia is sufficient for the diagnosis of melanoma in situ, acrolentiginous type.
Angulated, Hyperchromatic Nuclei in ALM at High MagnificationHigher magnification of same lesion shows angulated, hyperchromatic nuclei with scant amounts of cytoplasm . 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
Palms and soles
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
May remain flat or present as large, pigmented macule
Lesion becomes darker and more irregular as it progresses
Invasive areas may be associated with hyperkeratotic plaques, papules, nodules, and even ulceration
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
Wide surgical excision and amputation give comparable survival rates
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
5-year melanoma-specific survival rates: 80.3%
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. The lesion has a sharp border on the medial aspect 
. (Courtesy J. Finch, MD.)
is seen in this early in situ lesion. Only rare upward scatter 
of atypical melanocytes is identified. A Meissner corpuscle 
is seen in the dermis. There is marked uneven melanin incontinence 
.
and poorly nested growth pattern 
identified at the dermal-epidermal junction. There is only limited pagetoid upward scatter 
, unlike cutaneous melanoma. The finding of lentiginous growth with cytological atypia is sufficient for the diagnosis of melanoma in situ, acrolentiginous type.
. Note the melanocytic hyperplasia has replaced most of the basal keratinocytes.
