Melanoma In Situ in Thailand: Symptoms, Causes & Treatment | aihealz
Oncology
Melanoma In Situ.Care & specialists in Thailand
In Thailand, 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.
aliases · Melanoma In Situ (Stage 0 melanoma)· मेलानोमा इन सीटू· Mélanome in situ· Melanoma in situ· reviewed May 13, 2026
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Reviewed by AIHealz Medical Editorial Board · OncologyLast reviewed May 13, 2026
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).
key facts
Prevalence
Approximately 30,000 new US cases annually (SEER 2024); 30% of all new melanoma diagnoses
Demographics
Predominantly fair-skinned adults; median age 65 years; men slightly more affected than women
Avg. age
Median age at diagnosis 65; lentigo maligna subtype typically over 70
Global cases
Incidence highest in Australia, New Zealand, Norway, and the US
Specialist
Oncology
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How you might notice it
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..
01A pigmented skin lesion that has changed in size, shape, color, or surface texture over months to years — the most common presenting feature.
02Asymmetry of a pigmented lesion when divided through the center along any axis — one of the ABCDE warning criteria.
03Irregular, notched, or scalloped border that is poorly defined against surrounding skin.
04Two or more colors within a single lesion (brown, black, tan, red, pink, white, or blue), often with a streaky or speckled pattern.
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How it’s diagnosed
diagnosis
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.
Key tests
01
Total-body skin examination by a dermatologistIdentifies the suspicious lesion in context of the patient's other pigmented lesions; detects the 'ugly duckling' and assesses overall melanoma risk.
02
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Treatment & cost
medical treatments
✓Imiquimod 5% cream (topical)
✓Radiotherapy (definitive, fractionated; typically 45-50 Gy in 25 fractions or comparable hypofractionated schedule)
✓Cryotherapy (specialist use only)
surgical options
Wide local excision (5-10 mm margins)Histologic clearance in over 95% with 9-10 mm margins for non-lentigo-maligna subtypes; recurrence under 5%.
Mohs micrographic surgery with melanoma immunostainsLocal recurrence 1-2% at 5 years for lentigo maligna versus 6-20% with conventional excision (Higgins JAAD 2015).
Staged excision (slow Mohs or square procedure)Local recurrence 2-5% at 5 years; comparable to MART-1 Mohs.
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Causes & risk factors
known causes
Ultraviolet radiation (UV) exposure
Cumulative and intermittent UV exposure damages melanocyte DNA, generating signature C-to-T mutations at dipyrimidine sites and activating BRAF, NRAS, and other oncogenes. Severe blistering sunburns in childhood and adolescence are particularly strongly linked to later melanoma risk.
Tanning bed use
Indoor tanning emits high-intensity UVA and UVB radiation. Any use before age 35 increases melanoma risk by roughly 75% in pooled meta-analyses. The IARC has classified tanning devices as Group 1 carcinogens.
Genetic susceptibility (familial melanoma)
Germline CDKN2A, CDK4, BAP1, POT1, and MITF E318K variants confer high lifetime melanoma risk. Patients with two or more first-degree relatives with melanoma have a 35-70% lifetime risk depending on the variant.
Phenotypic susceptibility (fair skin, light eyes, red hair)
Fitzpatrick skin types I-II (always or usually burn, rarely tan), red or blond hair, blue or green eyes, and abundant freckling all reflect lower constitutive melanin protection. MC1R variants modulate this phenotypic risk.
Immunosuppression
Solid organ transplant recipients, hematopoietic stem cell transplant recipients, and patients on long-term immunosuppression have a 3-4 fold increased melanoma risk. Mechanism involves impaired tumor immunosurveillance combined with UV exposure.
High nevus count and atypical (dysplastic) nevi
Patients with more than 100 common nevi or 5 or more atypical nevi have markedly elevated melanoma risk. Atypical nevi can be markers of risk and occasionally precursors of new in situ disease.
risk factors
Fair skin and light pigmentation (Fitzpatrick I-II)
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Living with it
01Apply broad-spectrum SPF 30+ sunscreen daily to sun-exposed skin and reapply every 2 hours during outdoor activity
02Avoid tanning beds entirely — any use before age 35 raises melanoma risk by roughly 75%
03Wear photoprotective clothing, wide-brim hats, and UV-blocking sunglasses during peak UV hours (10 AM to 4 PM)
04Seek shade during peak UV hours; UV index applications guide planning
05Perform monthly self-skin examination with attention to new or changing lesions; partners can help check the back and scalp
06Annual full-body dermatology examination for adults with risk factors (fair skin, atypical nevi, family history, prior skin cancer)
recommended foods
•Vegetables and fruit rich in carotenoids and polyphenols for antioxidant support
•Oily fish for omega-3 fatty acids — modest observational evidence of skin cancer risk reduction
•
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When to seek help
why see an oncology
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.
Lentigo maligna (LM)Slowly enlarging irregularly pigmented macule on chronically sun-damaged skin of the head and neck of older adults. Accounts for 35-40% of in situ cases. Often present for years before diagnosis.
Superficial spreading melanoma in situFlat asymmetric pigmented lesion on intermittently sun-exposed skin of the trunk, back, and limbs. Most common subtype overall; presents in adults age 40-65.
Acral lentiginous melanoma in situArises on palms, soles, or nail units. Disproportionately affects people of color; longitudinal melanonychia with Hutchinson sign warrants biopsy.
Mucosal melanoma in situRare; arises on conjunctiva, oral cavity, nasal cavity, genital, or anorectal mucosa. Diagnosis is often delayed and surgical margins challenging.
Amelanotic in situLacks visible pigment; presents as a pink or skin-colored macule that mimics actinic keratosis or basal cell carcinoma. Easy to overlook clinically.
Living with Melanoma In Situ
Timeline
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.
Lifestyle
01Stop indoor tanning and discourage it among family members and adolescents
02Adopt sun-safe outdoor habits even in winter and at altitude
03Track changing lesions with smartphone photographs at fixed lighting to detect evolution
04Schedule lifelong dermatology follow-up after any melanoma diagnosis — 6-monthly for 5 years, then annually
05Educate household members on melanoma warning signs; familial clustering exists
06Continue vitamin D supplementation if dietary intake is low — sun avoidance can reduce cutaneous vitamin D synthesis
Daily management
01Apply broad-spectrum sunscreen daily to sun-exposed areas regardless of weather
02
Choosing a doctor
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.
Skin Cancer Foundation →Comprehensive patient information including prevention, detection, and treatment of melanoma.
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Frequently asked
What is melanoma in situ?▾▴
Melanoma in situ is the earliest stage of melanoma. Malignant melanocytes are confined entirely to the epidermis, the outermost layer of skin, without invading the dermis or having access to lymphatics.
Is melanoma in situ cancer?▾▴
Yes. Melanoma in situ is a true cancer because the cells are malignant — they show cytologic atypia and proliferate without normal regulation.
Can melanoma in situ become invasive melanoma?▾▴
Yes, if untreated or incompletely excised. Untreated melanoma in situ, particularly lentigo maligna, can progress to invasive melanoma over years. Complete surgical excision essentially eliminates this risk, which is why early diagnosis and treatment are so important.
How is melanoma in situ treated?▾▴
First-line treatment is wide local excision with 5-10 mm margins of clinically normal skin. For lentigo maligna and cosmetically sensitive sites, Mohs micrographic surgery with melanoma immunostains or staged excision is preferred to reduce recurrence.
What margins are recommended for melanoma in situ?▾▴
NCCN guidelines recommend 5-10 mm margins from the visible edge for melanoma in situ. Lentigo maligna often requires wider margins or comprehensive margin assessment (Mohs or staged excision) because subclinical extension is common.
Does melanoma in situ require a sentinel lymph node biopsy?▾▴
No. Sentinel lymph node biopsy is not indicated for true melanoma in situ because in situ disease lacks access to lymphatics and has no metastatic potential by definition.
What is lentigo maligna?▾▴
Lentigo maligna is a subtype of melanoma in situ that arises on chronically sun-damaged skin, classically the head and neck of older adults. It presents as a slowly enlarging irregularly pigmented macule.
What is the survival rate for melanoma in situ?▾▴
Five-year disease-specific survival exceeds 99% after complete excision. Long-term survival is essentially equivalent to the general population.
Can melanoma in situ come back after treatment?▾▴
Local recurrence is uncommon with adequate excision: 1-2% after Mohs or staged excision for lentigo maligna and 6-20% with conventional 5 mm margins for lentigo maligna. Non-lentigo-maligna in situ subtypes recur in under 5% after 9-10 mm margins.
Is melanoma in situ caused by sun exposure?▾▴
Most cases are linked to ultraviolet exposure. Lentigo maligna correlates with cumulative chronic sun exposure; superficial spreading in situ correlates with intermittent severe sunburns, especially in childhood. Tanning bed use before age 35 raises melanoma risk by roughly 75%.
How can I tell a mole from melanoma in situ?▾▴
Use the ABCDE criteria: Asymmetry, Border irregularity, Color variegation (two or more shades), Diameter typically over 6 mm, and Evolution (any recent change in size, shape, color, or symptoms). The ugly duckling sign — a lesion that looks different from your other moles — is also useful.
Does melanoma in situ run in families?▾▴
Familial melanoma accounts for roughly 5-10% of cases. Two or more first-degree relatives with melanoma, multiple primary melanomas in one individual, or melanoma plus pancreatic cancer in a family raises suspicion for germline variants like CDKN2A, CDK4, BAP1, POT1, or MITF E318K.
What is Mohs surgery for melanoma in situ?▾▴
Mohs micrographic surgery removes melanoma in situ in thin layers and examines 100% of the surgical margin under the microscope before further excision. Used with melanoma immunostains (MART-1, SOX10), it reduces local recurrence to 1-2% for lentigo maligna.
Can I use imiquimod cream instead of surgery for melanoma in situ?▾▴
Imiquimod 5% cream applied 5 days per week for 12 weeks produces clinical clearance in 70-80% of lentigo maligna. It is an alternative for patients unfit for or refusing surgery, or as adjuvant after positive Mohs margins.
How often should I see a dermatologist after melanoma in situ?▾▴
After excision, dermatology follow-up is typically every 6 months for the first 5 years, then annually. Total-body skin examinations search for new primary melanomas and inspect the scar for local recurrence.
Can melanoma in situ appear under a nail?▾▴
Yes. Acral lentiginous melanoma in situ can present as a new pigmented streak under a fingernail or toenail (longitudinal melanonychia). A streak wider than 3 mm, irregular pigmentation, or extension onto the surrounding nail fold skin (Hutchinson sign) warrants nail unit biopsy.
Does melanoma in situ affect people with dark skin?▾▴
Melanoma in situ is less common in people with darker skin but does occur. The acral lentiginous subtype on palms, soles, and nail units is disproportionately represented in people of color and is often diagnosed later. Total-body skin examination including acral surfaces and nails is recommended for all skin types.
What is the cost of melanoma in situ treatment?▾▴
Excisional biopsy and wide local excision range from USD 300 to 2,000 in the US depending on lesion size and reconstruction. Mohs surgery for lentigo maligna is typically USD 1,500-4,000. Most procedures are covered by insurance because melanoma is a malignancy. Costs in other markets vary widely.
Should I have my children screened for melanoma?▾▴
Routine pediatric melanoma screening is not recommended, but children of patients with familial melanoma, multiple primary melanomas, or known germline variants warrant dermatology surveillance starting in adolescence. Sun-protective habits established in childhood are the most important prevention strategy.
Is sunscreen enough to prevent melanoma in situ?▾▴
Sunscreen reduces but does not eliminate melanoma risk. Broad-spectrum SPF 30+ applied correctly and reapplied every 2 hours is part of comprehensive photoprotection that also includes UV-protective clothing, hats, sunglasses, shade during peak hours, avoiding tanning beds, and self-skin examinations.
Diameter greater than 6 mm, although in situ lesions can also be smaller — relative growth matters more than absolute size.
06Evolution over weeks to months — new appearance in adulthood, change in shape, or new symptoms such as itching, tenderness, or bleeding.
07A 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.
08A persistent flat or barely raised dark macule on the cheek, temple, or forehead of an older adult — classic lentigo maligna distribution.
09An 'ugly duckling' mole — a single lesion that visually differs from the patient's other pigmented lesions.
early warning signs
•Any new pigmented lesion appearing in adulthood, especially after age 40
•An existing mole that has begun to change in color, shape, or size
•Itching, tenderness, scaling, or bleeding in a pigmented lesion without explanation
•Personal history of atypical (dysplastic) nevi, especially in patients with strong family history of melanoma
•Childhood or adolescent severe blistering sunburns or extensive use of tanning beds before age 30
● emergency signs
•Sudden bleeding from a pigmented lesion without trauma — biopsy needed promptly to exclude invasive disease
•Rapid change (within weeks) in size or color of any pigmented lesion — urgent dermatology referral
•Ulceration of a pigmented lesion — strongly suggests invasion and requires same-week assessment
•New pigmented streak under a nail extending onto the adjacent skin (Hutchinson sign) — biopsy urgently
•Palpable lymph node near a known or suspected melanoma site — exclude regional metastasis, although unusual in true in situ disease
Dermoscopy (dermatoscopy)
Magnified skin examination that improves diagnostic sensitivity and specificity by 30-40% over naked-eye inspection. Identifies asymmetry of pigment, irregular network, regression, and other melanoma-specific features.
03
Excisional biopsy with 1-3 mm clinical marginGold-standard sampling. Removes the entire lesion with a narrow margin of normal skin, enabling complete histopathologic assessment of depth, margins, and features.
04
Histopathology with immunohistochemistry (Melan-A, MITF, SOX10)Confirms melanocytic origin, distinguishes in situ from invasive disease, and assists margin assessment in challenging cases like lentigo maligna.
05
Reflectance confocal microscopy (selected centers)Non-invasive in vivo imaging that visualizes individual cells at near-histologic resolution. Useful for mapping lentigo maligna margins and guiding biopsy of large facial lesions.
06
Staged excision (slow Mohs, square procedure) for lentigo malignaAchieves complete margin assessment for poorly demarcated lentigo maligna on the face. Reduces recurrence to 1-2% versus 6-20% with conventional excision at 5 mm margins.
Outlook
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.
non-modifiable
Lower constitutive melanin protection raises melanoma risk by 5-10 fold versus darker skin types. Red or blond hair and blue or green eyes amplify the risk through linked genetic pathways.
Cumulative and intermittent UV exposuremodifiable
Lifetime sun exposure correlates with lentigo maligna; intermittent severe sunburns correlate more strongly with superficial spreading melanoma. Outdoor occupations and tropical residence raise risk.
Indoor tanning before age 35modifiable
Raises melanoma risk roughly 75% in pooled meta-analyses. The IARC classifies tanning beds as Group 1 human carcinogens.
Atypical (dysplastic) nevimodifiable
Five or more atypical nevi confer a 6-10 fold elevated melanoma risk. Patients with familial atypical multiple mole melanoma syndrome require lifelong surveillance.
Family history of melanomagenetic
Two or more first-degree relatives with melanoma raises personal risk 30-70 fold depending on the underlying germline variant (CDKN2A, CDK4, BAP1, POT1, MITF E318K).
Personal history of prior melanoma or non-melanoma skin cancernon-modifiable
Prior melanoma raises subsequent melanoma risk roughly 9 fold; prior basal or squamous cell carcinoma also raises risk through shared UV exposure.
Age over 50non-modifiable
Lentigo maligna in particular peaks in the eighth and ninth decades, reflecting cumulative UV damage. Total melanoma incidence rises steadily with age.
Immunosuppression (transplant or chronic immunosuppressive therapy)modifiable
Solid organ transplant recipients have 3-4 fold elevated melanoma incidence. Calcineurin inhibitors and azathioprine contribute.
Adequate vitamin D from diet or supplements (800-2000 IU daily) to compensate for sun avoidance
•Green tea — observational studies suggest a protective association though evidence is limited
•Whole grains and lean protein for general dermatologic health
foods to avoid
•Excess alcohol — observational data link heavy intake to higher melanoma risk
•Tobacco smoking — worsens wound healing and overall cancer risk
•Diets very low in vitamin D and antioxidants if sun avoidance is strict
•Unproven supplements marketed for melanoma prevention without evidence
Self-examine skin monthly with attention to new lesions and changes in existing moles
03Attend scheduled dermatology surveillance every 6 months for the first 5 years
04Monitor surgical scar for any pigmented or thickened recurrence — report promptly
05Educate first-degree relatives about melanoma warning signs and risk
Exercise
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).