In Japan, melanoma In Situ is managed by oncologists. Melanoma in situ is the earliest detectable stage of melanoma — malignant melanocytes confined entirely to the epidermis above the basement membrane, with no invasion of dermis or potential to metastasize. It accounts for roughly 30% of new melanoma diagnoses in the United States (about 30,000 cases annually, SEER 2024) and incidence has risen 3-4% per year over two decades, driven mainly by ultraviolet exposure and improved dermoscopy-aided detection.
Melanoma in situ (ICD-10: D03) is malignant proliferation of melanocytes restricted to the epidermis, above the basement membrane. Because malignant cells have not crossed into the dermis, there is no access to lymphatics or blood vessels and therefore no biological capacity to metastasize. The American Joint Committee on Cancer classifies melanoma in situ as Stage 0 (Tis, N0, M0) under the AJCC 8th edition. Four major histologic subtypes are recognized: lentigo maligna (on chronically sun-damaged skin of the head and neck of older adults), superficial spreading in situ (the most common subtype, on intermittently sun-exposed skin of trunk and limbs), acral lentiginous in situ (on palms, soles, and nail units), and mucosal in situ (rare, on conjunctiva, oral, genital, or anorectal mucosa).
The key symptoms of Melanoma In Situ are: A pigmented skin lesion that has changed in size, shape, color, or surface texture over months to years — the most common presenting feature., Asymmetry of a pigmented lesion when divided through the center along any axis — one of the ABCDE warning criteria., Irregular, notched, or scalloped border that is poorly defined against surrounding skin., Two or more colors within a single lesion (brown, black, tan, red, pink, white, or blue), often with a streaky or speckled pattern., Diameter greater than 6 mm, although in situ lesions can also be smaller — relative growth matters more than absolute size., Evolution over weeks to months — new appearance in adulthood, change in shape, or new symptoms such as itching, tenderness, or bleeding., A new pigmented streak under a nail (longitudinal melanonychia) wider than 3 mm or extending onto adjacent nail fold skin (Hutchinson sign) — concerning for acral or subungual disease..
Diagnosis follows the 2019 AAD melanoma guidelines (Swetter JAAD 2019) and the current NCCN melanoma guideline. The pathway begins with clinical examination using the ABCDE criteria (Asymmetry, Border irregularity, Color variegation, Diameter, Evolution) and the ugly duckling sign. Dermoscopy raises diagnostic sensitivity and specificity substantially: superficial spreading in situ shows asymmetric pigment network with abrupt cut-off, irregular dots, and regression structures; lentigo maligna shows asymmetric pigmented follicular openings and rhomboidal structures on chronically sun-damaged skin. Any clinically or dermoscopically suspicious lesion warrants biopsy. The preferred technique is excisional biopsy with 1-3 mm margins of clinically normal skin extending into subcutaneous fat. This allows accurate determination of Breslow thickness, ulceration, mitotic rate, and most importantly distinguishes in situ from invasive disease. Partial biopsies (incisional, punch, shave) are acceptable only on cosmetically sensitive sites such as the face or acral surfaces, with the understanding that they may sample non-representative areas. Histopathologic diagnosis of melanoma in situ requires demonstration of malignant melanocytes confined to the epidermis with characteristic features: nested and single-cell proliferation along the dermo-epidermal junction, pagetoid scatter into upper epidermis, cytologic atypia, and confluent growth. Immunohistochemistry (Melan-A, MITF, SOX10) confirms melanocytic origin and aids margin assessment. Lentigo maligna in particular requires careful margin evaluation because subclinical extension is common — many surgeons employ staged excision (slow Mohs or square procedure) for adequate clearance. Sentinel lymph node biopsy is not indicated for true in situ disease because there is no metastatic potential by definition.
Prognosis after complete excision of true melanoma in situ is excellent. Five-year disease-specific survival exceeds 99% because in situ lesions have no biological access to lymphatics or blood vessels. The dominant residual risks are local recurrence (1-2% with Mohs or staged excision for lentigo maligna; 6-20% with conventional 5 mm excision) and the development of a second primary melanoma elsewhere on the skin (roughly 9-fold elevated lifetime risk versus the general population). Recurrent lentigo maligna can progress to lentigo maligna melanoma (invasive disease) if neglected — long-term dermatology surveillance is therefore essential. Adverse factors include incomplete excision margins, large lentigo maligna (>3 cm), and the lentigo maligna subtype on cosmetically constrained sites such as the eyelid or nasal ala. Favorable factors include early detection, small lesion size, clear margins documented with comprehensive margin assessment, and patient adherence to surveillance and photoprotection.
A dermatologist with melanoma expertise should manage diagnosis and surgical planning. Mohs surgeons or surgical oncologists are involved for cosmetically challenging or anatomically complex lentigo maligna of the face. Patients with familial melanoma, multiple primary melanomas, or strong family history warrant genetic counseling for CDKN2A and other germline variants. Multidisciplinary tumor boards review difficult lentigo maligna cases.
Find specialists →Surgical wounds typically heal in 2-3 weeks. Sutures are removed in 7-14 days depending on site and tension. Sun protection of the scar is essential for 6-12 months. Lentigo maligna treated with staged excision or Mohs may involve 1-2 weeks of multiple visits before final reconstruction; complex reconstructions on the face may take additional weeks of healing. Dermatology surveillance begins at 3-6 months post-procedure and continues every 6 months for the first 5 years, then annually.
Regular outdoor exercise is encouraged with sun-safe planning — protective clothing, sunscreen, and hat in daylight hours. Indoor cardio and resistance training are appropriate during peak UV periods. No exercise restrictions follow melanoma in situ excision once the wound has healed (usually 2-3 weeks).
Look for board-certified dermatologists or surgical oncologists with melanoma-specific volume, on-site dermoscopy, access to Mohs surgery with melanoma immunostains for facial lesions, and integration with dermatopathology. Tertiary cancer centers offer staged excision, reflectance confocal microscopy, and clinical trials for advanced lentigo maligna.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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