Melanoma

• UV-Induced Mutagenesis and BRAF/NRAS Mutations: Ultraviolet radiation (particularly UVB at 280-320 nm) causes direct DNA damage through formation of cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts, leading to characteristic C→T transition mutations at pyrimidine-pyrimidine dinucleotides. Approximately 50-70% of melanomas harbor activating mutations in BRAF (most commonly V600E), which constitutively activates the MAPK/ERK signaling cascade independent of upstream growth factor stimulation, driving uncontrolled proliferation. BRAF mutations are associated with intermittent sun exposure patterns (e.g., recreational sunbathing) and are most common in cutaneous melanomas. Conversely, 15-30% of melanomas contain NRAS mutations (predominantly Q61), which activate both MAPK and PI3K/AKT pathways, and these are associated with chronic sun exposure and older age of onset. The remaining 20-30% of melanomas are "wild-type" (BRAF/NRAS-negative) and often harbor alterations in NF1 (neurofibromin), KIT, or GNAQ/GNA11 (particularly in uveal and acral melanomas), representing molecularly distinct disease subtypes with different therapeutic sensitivities.

• TP53 Loss and Checkpoint Dysregulation: Loss or mutation of the TP53 tumor suppressor gene (observed in 40-50% of melanomas) ablates p53-mediated cell cycle arrest and apoptosis in response to DNA damage, enabling genomic instability and progression. Additionally, inactivation of PTEN (via mutation or deletion) dysregulates the PI3K/AKT/mTOR pathway, reducing apoptosis and enhancing survival signaling. These alterations facilitate the transition from benign melanocytic lesions (nevi) through dysplastic nevi to primary melanoma and ultimately to metastatic disease, with accumulating mutations correlating with increasing malignant potential.

• Immune Evasion and Checkpoint Ligand Expression: Melanoma cells progressively evade immune surveillance through upregulation of immune checkpoint ligands, including PD-L1 (programmed death ligand 1) and PD-L2, which engage PD-1 receptors on T cells, suppressing T cell receptor signaling and promoting T cell exhaustion and apoptosis. CTLA-4 (cytotoxic T lymphocyte antigen 4) on regulatory T cells similarly suppresses anti-tumor immunity. Melanomas also secrete immunosuppressive cytokines (IL-10, TGF-β) and recruit myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) to the tumor microenvironment, creating an immunosuppressive milieu that permits tumor escape from endogenous anti-tumor immunity. This mechanism explains the dramatic efficacy of immune checkpoint inhibitors (anti-PD-1 and anti-CTLA-4 agents) in reversing T cell exhaustion and unleashing potent anti-tumor immunity.

• Melanoma-Initiating Cells and Stem Cell Properties: A subset of melanoma cells exhibit enhanced self-renewal capacity and resistance to apoptosis, functioning as cancer stem cells or melanoma-initiating cells. These cells express elevated levels of markers such as CD271 and possess enhanced tumorigenicity and metastatic capacity. They also display intrinsic resistance to standard therapies, contributing to treatment failures and relapse. The epithelial-to-mesenchymal transition (EMT) is activated in melanomas, with downregulation of E-cadherin and upregulation of transcription factors such as SNAIL, SLUG, and ZEB1, promoting migration, invasion, and dissemination.

• Angiogenesis and Vascular Co-option: Melanomas promote neovascularization through VEGF (vascular endothelial growth factor) secretion and through recruitment of vasculogenic mimicry—formation of vessel-like structures by melanoma cells themselves. Additionally, melanomas can co-opt existing vasculature without initiating new vessel formation, facilitating rapid growth and metastasis. The vascular network provides access for dissemination to regional lymph nodes and distant organs, with lymphangiogenesis similarly promoting lymphatic spread.

• Increased Mitotic Rate and Reduced Differentiation: Malignant transformation correlates with a marked increase in the mitotic index (number of mitoses per high-power field), reflecting uncontrolled proliferation. Concurrent loss of melanocytic differentiation markers (such as decreased MELAN-A/MART-1 or SOX10 expression) indicates dedifferentiation, which correlates with increased aggressiveness and metastatic potential. Spindle cell and epithelioid morphologies are associated with higher-grade disease compared to the small-cell variant.

• Ultraviolet (UV) Radiation Exposure: UV exposure (both UVA and UVB) is the most significant and modifiable risk factor for melanoma development. Intermittent, high-intensity sun exposure (particularly during childhood and adolescence) and episodes of severe sunburn carry the highest risk and are associated with BRAF-mutant melanomas. Chronic cumulative sun exposure increases risk but is associated with different molecular profiles (NRAS mutations, older age). Paradoxically, occupational sun exposure (leading to chronic, low-intensity exposure) carries lower melanoma risk than recreational sun exposure, likely due to development of protective tanning response and behavioral adaptation. Indoor tanning bed use, which emits primarily UVA radiation in high concentrations, increases melanoma risk by approximately 75% with every 10 years of use before age 30.

• Family History and Hereditary Syndromes: Approximately 5-10% of melanomas are familial, often associated with hereditary melanoma syndromes. The most common is CDKN2A/p16 syndrome (familial atypical mole-malignant melanoma or FAMMM syndrome), caused by germline mutations in the CDKN2A gene encoding the p16 cyclin-dependent kinase inhibitor; carriers have a lifetime melanoma risk exceeding 75%. Other hereditary syndromes include CDK4 mutations and BAP1 mutations (which predispose to uveal melanoma and mesothelioma in addition to cutaneous melanoma). A family history of melanoma increases an individual's risk 8-10 fold.

• Phenotypic Features and Dysplastic Nevi: Fair skin, red or blonde hair, blue eyes, and inability to tan significantly increase melanoma risk. The presence of dysplastic (atypical) nevi is a strong risk factor; these are clinically atypical nevi with irregular borders, variegated colors, and irregular surfaces, representing a precursor state and a marker of increased susceptibility. Individuals with >50 dysplastic nevi have an approximate 10% lifetime risk of developing melanoma. The presence of >100 benign nevi similarly increases risk.

• Immunosuppression: Patients with chronic immunosuppression (such as organ transplant recipients on calcineurin inhibitors or those with HIV/AIDS) have 10-100 fold increased melanoma risk, reflecting the critical role of immune surveillance in preventing melanoma development. Similarly, patients treated with tumor necrosis factor (TNF)-α inhibitors for rheumatologic conditions have modestly increased risk.

• Hormonal Factors: Pregnancy and exogenous estrogen use (oral contraceptives, hormone replacement therapy) are associated with slightly increased melanoma risk and potentially accelerated progression in existing melanoma, though the magnitude of increased risk is modest (approximately 1.3-fold). Estrogen-responsive signaling may promote melanoma growth, and these factors should be considered in risk-benefit discussions but do not constitute absolute contraindications in appropriate clinical contexts.

• Prior Melanoma or Non-melanoma Skin Cancer: Individuals with a history of melanoma have a 5-10% risk of developing a second primary melanoma, and the presence of prior keratinocyte carcinomas (basal cell or squamous cell carcinoma) indicates chronic UV-induced skin damage and increases future melanoma risk.

• Large Congenital Nevi: Congenital melanocytic nevi, particularly giant variants (>20 cm), carry a lifetime risk of malignant transformation to melanoma of 5-10%, and surveillance is recommended.

• ABCDE Criteria and Asymmetry: The ABCDE mnemonic captures essential clinical features of melanoma and guides recognition: A (Asymmetry) indicates that one half of the lesion does not mirror the other, reflecting the irregular growth pattern typical of melanoma; this is the most sensitive single feature. Asymmetry emerges because melanomas lack the organized, circumscribed growth pattern of benign nevi and instead exhibit random directional growth driven by clonal heterogeneity and differential growth rates of neoplastic subclones.

• Border Irregularity (B): Melanomas characteristically display irregular, notched, or scalloped borders rather than the sharp, well-demarcated borders of benign nevi. This reflects the infiltrative growth pattern of melanoma, with single cells and small nests of melanoma cells extending beyond the clinically apparent lesion margin, a phenomenon termed "microsatellites." Careful clinical examination may reveal subtle color variation at the border itself.

• Color Variegation (C): Melanomas typically display multiple colors within a single lesion, including brown, black, red, white, and blue—a feature termed polychromy. Different colors reflect different depths of pigmentation and melanin distribution: brown and black indicate more superficial pigmentation, blue results from Tyndall scattering of light at deeper dermal levels (Rayleigh scattering), and red or pink represents inflammation or increased vascularity at the lesion edge. White areas may indicate areas of regression, spontaneous immune destruction with loss of melanocytes and fibrosis. Benign nevi typically display uniform coloration throughout.

• Diameter (D): A diameter >6 mm (approximately the width of a pencil eraser) is a concerning feature and warrants biopsy, though the 6 mm rule is not absolute—melanomas can be smaller (particularly lentigo maligna melanomas, which may be subtle), and some benign nevi exceed 6 mm. Nonetheless, rapidly enlarging lesions of any size warrant urgent evaluation.

• Evolution (E): Recent change in size, shape, or color is a critical warning sign. Patients frequently report that a lesion has changed over weeks to months—enlarging, darkening, becoming itchy or bleeding. This represents dynamic progression of malignancy and is highly predictive of melanoma.

• Additional Clinical Features: Beyond ABCDE, bleeding, ulceration, itching, or tenderness are concerning features suggesting deeper invasion and increased malignancy. Pruritus may result from inflammatory mediators released by tumor-infiltrating lymphocytes. Paresthesias or numbness suggest neural involvement. The ugly duckling sign—a lesion that looks distinctly different from all other lesions on an individual's body—is a practical clinical tool with high sensitivity for melanoma detection.

• Clinical Subtypes and Presentation Patterns: Superficial Spreading Melanoma (SSM) is the most common subtype (60-70% of cases) and presents as an expanding, irregular, multi-colored patch or thin plaque, often on the trunk, extremities, or face. Nodular Melanoma (NM) presents as a rapidly growing, often darkly pigmented nodule and has the poorest prognosis stage-for-stage due to early vertical (dermal) invasion; it may lack the characteristic flat component seen in other subtypes. Lentigo Maligna Melanoma (LMM) occurs on chronically sun-exposed skin (particularly the face and ears) in elderly patients and presents as a large, irregular, variably pigmented patch with slow growth over years; it evolves from lentigo maligna (melanoma in situ) in the dermis. Acral Lentiginous Melanoma (ALM) occurs on palms, soles, and nail beds (particularly the hallux), presents with ill-defined brown or black discoloration, and accounts for the majority of melanomas in individuals with darker skin tones; it is associated with worse prognosis due to delayed diagnosis and anatomically challenging location. Mucosal Melanoma arises from melanocytes in mucous membranes (oral cavity, nasopharynx, anorectum, urogenital tract) and presents with dark discoloration, bleeding, or obstruction; it carries very poor prognosis due to late presentation and aggressive biology.

• Amelanotic Melanoma: Approximately 5-10% of melanomas are amelanotic or hypomelanotic, lacking significant pigmentation and presenting as pink, red, or flesh-colored nodules or plaques. These are frequently mistaken for benign entities such as basal cell carcinoma, dermatofibroma, or hemangioma, leading to diagnostic delay and more advanced stage at presentation. A high degree of clinical suspicion is required.

• Physical Examination Findings: Beyond the lesion itself, examination should assess regional lymph nodes for enlargement (palpable nodes >1 cm in the region draining the primary lesion warrant biopsy or imaging) and in-transit metastases (satellite lesions within 2 cm of primary; microsatellites between 2 cm and first regional node station). Hepatomegaly or other signs of visceral metastasis may be evident in advanced disease.

• Clinical Assessment and ABCDE Criteria: The diagnostic approach begins with clinical recognition using the ABCDE criteria discussed above. Any lesion meeting ≥3 ABCDE criteria or displaying the "ugly duckling sign" warrants biopsy. Dermoscopy (epiluminescence microscopy), a non-invasive technique using magnification and polarized light to visualize subsurface structures, improves diagnostic accuracy to 95% in expert hands and identifies specific patterns such as asymmetric growth pattern, atypical network (irregular pigmentation pattern at lesion periphery), atypical dots/globules, and blue-white veil (benign vascular pattern overlaid with atypical pigmentation). Dermoscopy is particularly useful for evaluating equivocal lesions and for surveillance of high-risk individuals.

• Skin Biopsy and Histopathology: The gold standard for melanoma diagnosis is excisional biopsy with narrow (1-3 mm) margins, allowing complete histologic examination and accurate measurement of Breslow thickness—the most critical prognostic variable. Incisional or punch biopsy is acceptable if excisional biopsy would cause substantial morbidity (e.g., on the face). Specimens should be oriented by the pathologist to assess peripheral and deep margins. Histology reveals melanoma cells—often with increased nuclear size, irregular nuclear membranes, prominent nucleoli, and elevated mitotic rates—arranged in nests within the epidermis and dermis. Key histologic features include:
• Breslow thickness: Vertical distance from the granular layer to the deepest tumor cell, measured in millimeters; this is the single strongest prognostic factor, with 5-year survival declining from >90% at ≤1 mm to <30% at >4 mm.
• Clark level: Anatomic depth of invasion (I: confined to epidermis; II: invasion into papillary dermis; III: filling the papillary dermis; IV: invasion into reticular dermis; V: invasion into subcutaneous fat). Clark level is less reliable than Breslow thickness for prognostic stratification but provides contextual information.
• Mitotic rate (per mm²): Elevated mitotic rate (>

Definitive local therapy (all stages)

• Wide local excision (WLE): the curative backbone. Per NCCN Cutaneous Melanoma guidelines, margins are dictated by Breslow thickness — roughly 0.5–1 cm for melanoma in situ, 1 cm for tumors ≤1 mm, 1–2 cm for >1–2 mm, and 2 cm for >2 mm. Wider margins do not improve survival, so the excision is thickness-matched, not maximal.
• Sentinel lymph node biopsy (SLNB): performed at the time of WLE (lymphatic mapping is unreliable once the basin is disrupted). ASCO/SSO recommend against SLNB for thin T1a lesions, consider it for T1b, and recommend it for intermediate-thickness (>1 mm) melanoma. It is a staging/prognostic test.
• Completion lymph node dissection is no longer routine for a positive sentinel node; MSLT-II showed no melanoma-specific survival benefit, so nodal ultrasound surveillance is preferred. This is a favorite exam update.

Adjuvant therapy after resection (stage IIB–III)

• Anti–PD-1 antibodies (pembrolizumab, nivolumab): reverse T-cell exhaustion; NCCN-endorsed adjuvant standard, improving recurrence-free survival.
• BRAF + MEK inhibitor pairs (dabrafenib plus trametinib) for resected BRAF V600–mutant stage III disease.

Unresectable or metastatic disease

• First line — immune checkpoint blockade: anti–PD-1 monotherapy, or combinations such as nivolumab plus ipilimumab (anti–CTLA-4) or nivolumab plus relatlimab (anti–LAG-3). Combinations give higher response rates, including intracranial activity, at the cost of far more immune-related toxicity.
• Targeted therapy: for BRAF V600–mutant tumors, a BRAF inhibitor always paired with a MEK inhibitor (dabrafenib/trametinib, encorafenib/binimetinib) — faster responses, less durable than immunotherapy.
• Oncolytic and local options: intralesional talimogene laherparepvec for injectable cutaneous/nodal lesions; stereotactic radiosurgery for brain metastases; palliative radiation for bone or symptomatic sites.

Contraindicated or obsolete

• Deep shave or transecting biopsy of a suspicious pigmented lesion — destroys Breslow measurement.
• BRAF inhibitor monotherapy and its use in BRAF wild-type tumors (paradoxical MAPK activation).
• Elective/prophylactic complete lymphadenectomy and cytotoxic chemotherapy (dacarbazine) as first line.
• Checkpoint inhibitors are used with great caution in active autoimmune disease and organ transplant recipients (rejection risk).

Complications of the disease

• Distant metastasis: melanoma spreads lymphatically and hematogenously to essentially any organ — lung, liver, bone, brain, and characteristically skin/subcutis and small bowel. Signalled by new neurologic deficits, a rising LDH, or new nodules on surveillance imaging.
• Hemorrhagic brain metastases — emergency. Melanoma is among the classic causes of bleeding intracranial metastases (with renal cell, choriocarcinoma, thyroid). Headache, seizure, or focal deficit warrants urgent non-contrast CT then MRI; herniation risk mandates neurosurgical/steroid input.
• Small-bowel metastasis with obstruction or intussusception — emergency. Adult intussusception is pathologic until proven otherwise, and melanoma is the classic metastatic lead point.
• In-transit/satellite metastases: tumor emboli trapped in dermal lymphatics between the primary and the nodal basin; appear as new pigmented papules along the drainage path and upstage the patient.
• Second primary melanoma: field UV damage means these patients need lifelong skin surveillance.

Complications of treatment

• Immune-related adverse events (irAEs) from checkpoint inhibitors: loss of peripheral tolerance produces autoimmune inflammation of any organ — colitis (diarrhea, perforation risk), hepatitis (transaminitis), pneumonitis (dyspnea, ground-glass opacities), thyroiditis, hypophysitis, and type 1 diabetes. Per ASCO/NCCN irAE guidance, management is drug interruption plus systemic corticosteroids, with infliximab for steroid-refractory colitis (avoided in hepatitis).
• Checkpoint inhibitor myocarditis — emergency: rare but highly lethal; elevated troponin, new conduction block or arrhythmia. Requires immediate drug cessation and high-dose steroids.
• Hypophysitis with secondary adrenal insufficiency — emergency if it presents as adrenal crisis (hypotension, hyponatremia); give stress-dose glucocorticoid before any further workup. Classically ipilimumab.
• BRAF/MEK inhibitor toxicity: paradoxical MAPK activation in RAS-mutant keratinocytes causes cutaneous squamous cell carcinoma and keratoacanthomas (mitigated by adding a MEK inhibitor); also pyrexia, MEK-related retinopathy and decreased ejection fraction, and QT prolongation.
• Surgical: lymphedema, seroma, and nerve injury after nodal dissection.
• Vitiligo-like depigmentation during immunotherapy reflects on-target melanocyte immunity and is a favorable prognostic sign, not treatment failure.

• Single best next step for a suspicious pigmented lesion: full-thickness excisional biopsy with narrow (1–3 mm) margins. Not a deep shave, not cryotherapy, not "reassure and recheck in 6 months" — transecting the base destroys the Breslow measurement that drives every subsequent decision.
• Breslow depth is the dominant prognostic variable in localized disease; ulceration independently worsens stage in AJCC 8th edition. Clark level is the classic distractor — it is largely historical and inferior to Breslow.
• Immunohistochemistry: S-100 is the most sensitive melanoma marker; HMB-45, Melan-A/MART-1, and SOX10 are more specific. SOX10 is the go-to for spindle-cell and desmoplastic variants that lose other markers.
• The association examiners love: BRAF V600E → MAPK pathway activation → treat with a BRAF inhibitor plus a MEK inhibitor. Single-agent BRAF inhibition, or use in BRAF wild-type tumors, causes paradoxical MAPK activation and squamous neoplasms.
• Know the checkpoint targets cold: ipilimumab = CTLA-4; nivolumab/pembrolizumab = PD-1; relatlimab = LAG-3. A patient on any of these with new diarrhea, dyspnea, transaminitis, or hypotension has an irAE until proven otherwise — hold the drug and give corticosteroids.
• Hutchinson sign: pigment extending from a nail-bed lesion onto the proximal nail fold — subungual acral lentiginous melanoma, not a subungual hematoma (a hematoma grows out with the nail).
• Acral lentiginous melanoma is the most common subtype in patients with darker skin, but melanoma incidence overall remains far higher in fair-skinned individuals — the classic distractor is inverting these two statements.
• Nodular melanoma lacks a radial growth phase and invades vertically early, giving the worst prognosis stage-for-stage; amelanotic melanoma is the pink papule misdiagnosed as a basal cell carcinoma or pyogenic granuloma.
• Screening: the USPSTF has found insufficient evidence for routine whole-body visual skin examination in asymptomatic average-risk adults — surveillance is targeted at high-risk patients (prior melanoma, FAMMM/CDKN2A, numerous atypical nevi).