Acral lentiginous melanoma (ALM) is a rare form of skin cancer. This melanoma originates in melanocytes, the cells producing skin pigment. While the overall incidence of ALM is low, it represents a significant proportion of melanoma cases in individuals with darker skin tones and those of Asian descent.
Understanding Acral Lentiginous Melanoma
Acral lentiginous melanoma is a distinct melanoma subtype that typically appears on non-hair-bearing skin: the palms, soles, and beneath the nails. Unlike most other forms of melanoma, ALM is not strongly associated with exposure to ultraviolet (UV) radiation from the sun. The exact causes of ALM are not fully understood, but some theories suggest a possible link to mechanical stress, trauma, pressure, or friction in these areas.
ALM often begins as a flat, discolored mark that can be light to dark brown, or even black. It may also appear as an amelanotic lesion, lacking dark pigment and can be reddish or orange. Initially, the lesion might be small and mistaken for a bruise or stain, but it tends to enlarge over time. ALM has a radial growth phase where it spreads superficially along the skin’s surface or under the nail bed before potentially invading deeper layers. This growth can take months to years to become invasive.
When ALM develops under a nail, it often presents as a dark, narrow streak running vertically. This is known as subungual melanoma. As the lesion progresses, the nail may show signs of damage, such as cracking or breaking.
Identifying Signs in Children
Recognizing ALM signs in children requires careful observation, as these lesions can sometimes resemble common benign conditions. Parents and caregivers should regularly inspect their child’s palms, soles, and nail areas for any new or changing spots. A new or evolving spot or patch on the hands or feet, especially one with irregular borders or varying colors, warrants attention. These spots may be dark, reddish, pinkish, or orange.
On the palms and soles, ALM might appear as a flat, pigmented area that changes in size, shape, or color. It can sometimes be mistaken for a wart, callus, or even a bruise. Any spot that is growing, itching, bleeding, or causing pain should be evaluated by a healthcare professional.
When ALM affects the nails, it often presents as an unexplained dark streak running vertically down the nail plate. This streak may widen over time or cause the nail to crack or become distorted. Pigment extending from under the nail onto the surrounding skin of the nail fold, known as Hutchinson’s sign, is a concerning indicator. Any new or changing streak should prompt a medical consultation.
Diagnostic Process and Treatment Options
Diagnosing ALM in children typically begins with a dermatologist’s thorough clinical examination, often using a dermatoscope. If melanoma is suspected, a biopsy is necessary for microscopic examination. An excisional biopsy, where the entire suspicious lesion is removed, is often preferred for smaller lesions for complete pathological assessment. For larger lesions or those in sensitive areas, an incisional or punch biopsy, removing only a portion, may be performed.
Following the biopsy, a pathologist examines the tissue to confirm the presence of melanoma and assess its characteristics, such as thickness (Breslow depth) and presence of ulceration. If the melanoma is confirmed, further staging tests may be conducted to determine if the cancer has spread, which could include imaging scans or a sentinel lymph node biopsy. A sentinel lymph node biopsy identifies and removes the first lymph node(s) likely to be affected to check for microscopic metastasis.
The primary treatment for ALM is surgical removal of the tumor with a margin of healthy surrounding tissue. The size of this margin depends on the melanoma’s thickness. For very thin lesions (in-situ), a margin of 0.5 to 1 cm might be sufficient, while thicker lesions (over 2 mm Breslow depth) may require a 2 cm margin. In cases of subungual melanoma, a partial amputation of the affected digit might be necessary to ensure complete removal and preserve function. Depending on the cancer’s stage and if it has spread, additional treatments like immunotherapy, targeted therapy, radiation therapy, or chemotherapy may be considered.
Outlook and Ongoing Care
The outlook for children diagnosed with ALM is more favorable with early detection and treatment. Early diagnosis allows for removal before the cancer has had a chance to invade deeper or spread to other parts of the body. The prognosis is influenced by factors such as the tumor’s thickness, whether it has ulcerated, and if it has spread to lymph nodes. While ALM can have a poorer prognosis compared to other melanoma types in some studies, this is often linked to delayed diagnosis, which can lead to more advanced disease at presentation.
After treatment, ongoing monitoring is important for long-term care for children with ALM to check for any signs of recurrence or the development of new lesions. This typically involves regular follow-up appointments with a multidisciplinary team, which may include dermatologists, oncologists, and surgeons. These appointments help ensure that any changes are identified promptly, allowing for swift intervention if needed.