Diagnosis: Lentigo maligna melanoma

This patient had lentigo maligna melanoma, a cancerous lesion that most commonly arises as a tan or brown macule on sun-damaged surfaces of the skin.3 The lesion acquires a darker, asymmetrical appearance as it enlarges. When it is nonpalpable and still confined to the dermis, it is known as “malignant melanoma in situ, lentigo maligna type.” Five percent eventually become palpable, indicating dermal invasion and conversion to lentigo maligna melanoma.4 This transformation is typically very gradual, and the lesion may be present for up to 50 years before the vertical growth phase begins. 

The lesion is characterized by an irregular border, resulting in a “geographic” shape, with inlets and peninsulas. Multiple colors are possible, including brown, tan, blue, gray, black, pink, or white. With transformation to the vertical phase, the lesion will be palpable, with focal papular or nodular components. Partial regression of the lesion is not uncommon and presents as a gray or blue-gray discoloration. Monitoring for regional lymphadenopathy is crucial, as the lesion has the potential for metastasis once the vertical growth phase has been reached. Evidence of sun damage in these patients is almost universal.

The differential diagnosis includes seborrheic keratosis and solar lentigo. As previously noted, seborrheic keratoses may be dark, and early lesions may not yet have the classic palpable “warty” surface that exhibits fine scale with scratching. Solar lentigo is the nonpalpable, in situ lesion that spreads laterally and has not yet acquired the vertical growth phase component, which then classifies it as lentigo maligna melanoma.

All lesions suspected of being lentigo maligna melanoma should be biopsied. One may find either singly dispersed or nests of atypical melanocytes invading the dermis. Poorly cohesive nests (“swallow’s nest” sign) at the dermal-epidermal junction and convergence of melanocytes at the basal layer of the epidermis are often harbingers of the invasive stage.5 Multinucleated giant melanocytes with hyperchromatic nuclei,
also known as “star-burst giant cells,” may be found at the basal layer of the epidermis.6 Microstaging via the Clark or Breslow system and staging of the melanoma in accordance with the American Joint Commission on Cancer is recommended.

Management includes excision with margins >1 cm beyond the clinically visible lesion. If the tumor is >2 mm in depth, the standard of care is to excise with 2-cm margins.7,8 Excision should extend down to the fascia; a graft may be needed. Unless lymph nodes are clinically palpable, node dissection is not recommended. A sentinel node biopsy may be performed if the lesion is >1.5 mm in thickness. In patients older than 60 whose lesions are between 1.5 and 4 mm thick, elective lymph node dissection may be advantageous.9 Despite the potential to metastasize, surgical outcome is very favorable. Recurrence is possible, but mortality from dissemination is rare.10

Our patient’s lesion had a nodular quality on palpation, but he had no lymphadenopathy. The lesion measured 8 x 9 mm, and the diagnosis was confirmed by biopsy and staged at Clark level I, Breslow stage II. Excision with 1-cm margins was performed, and a flap was constructed because primary closure at the site was unattainable. The patient has made frequent follow-up visits and is doing well, with no recurrences one year later.

Dr. Conley is a Family Physician in Manhattan Beach, Calif. Dr. Buka is a dermatologist in New York City.

References

1. Helm KF, Marks JG Jr. Atlas of Differential Diagnosis in Dermatology. New York, N.Y.: Churchill Livingstone; 1998:236-238.
2. Thompson SC, Jolley D, Marks R. Reduction of solar keratoses by regular sunscreen use. N Engl J Med. 1993;329:1147-1151.
3. Clark WH Jr, Mihm MC Jr. Lentigo maligna and lentigo maligna melanoma. Am J Pathol. 1969;55:39-67.
4. Weinstock MA, Sober AJ. The risk of progression of lentigo maligna to lentigo maligna melanoma. Br J Dermatol. 1987;116:303-310.
5. Tannous ZS, Lerner LH, Duncan LM, et al. Progression to invasive melanoma from malignant melanoma in-situ, lentigo maligna type. Hum Pathol. 2000;31:705-708.
6. Cohen LM. Lentigo maligna and lentigo maligna melanoma. J Am Acad Dermatol. 1995;33:923-936.
7. Khayat D, Rixe O, Martin G, et al. Surgical margins in cutaneous melanoma (2 cm versus 5 cm for lesions measuring less than 2.1 mm thick). Cancer. 2003;97:1941-1946.
8. Cohn-Cedermark G, Rutqvist LE, Andersson R, et al. Long term results of a randomized study by the Swedish Melanoma Study Group on 2-cm versus 5-cm resection margins for patients with cutaneous melanoma with a tumor thickness of 0.8-2.0 mm. Cancer. 2000;89:1495-1501.
9. Sealy D. Melanoma. In: Dambro MRR, ed. Griffith’s Five Minute Clinical Consult. Baltimore, Md.: Lippincott Williams and Wilkins; 2004: chap 34.
10. Sober AJ. Screening for skin cancers. In: Goroll AHH, Mulley AG, Goroll AH, May LA, eds. Goroll’s Primary Care Medicine. Baltimore, Md.: Lippincott Williams & Wilkins; 2000: chap 177.