Melanoma

Melanoma – High‑Yield Study Guide for Medical Students

Definition

Melanoma is a malignant tumor of melanocytes arising most commonly in the skin, but it can also develop in mucosal surfaces, the uveal tract of the eye, and other sites containing melanocytes. It is characterized by high metastatic potential, early lymphovascular spread, and significant mortality compared with other skin cancers. Cutaneous melanoma includes several histologic subtypes (superficial spreading, nodular, lentigo maligna, acral lentiginous), each with characteristic clinical and pathological features.

Epidemiology

Melanoma is one of the most common malignancies in fair‑skinned populations and is a leading cause of skin cancer–related death worldwide. Incidence has been rising over recent decades, particularly in younger and middle‑aged adults, largely attributed to increased ultraviolet (UV) exposure and behavioral patterns such as intermittent intense sun exposure and tanning bed use. Melanoma is more frequent in individuals with Fitzpatrick skin types I–II and less common but often diagnosed later and at more advanced stages in people with skin of color, contributing to worse outcomes in these populations.^{[3](https://pubmed.ncbi.nlm.nih.gov/41773219/)}

Pathophysiology

Melanoma develops from malignant transformation of melanocytes through the accumulation of genetic and epigenetic alterations, often triggered or promoted by UV radiation–induced DNA damage. UVB and UVA radiation cause cyclobutane pyrimidine dimers, oxidative damage, and mutational signatures that affect key regulatory genes, including those involved in cell cycle control, apoptosis, and MAPK signaling. The tumor microenvironment, immune surveillance, and interactions with keratinocytes and stromal cells also influence melanoma initiation and progression.

Approximately 40–50% of cutaneous melanomas harbor activating BRAF mutations (most commonly V600E), which constitutively activate the MAPK (RAS–RAF–MEK–ERK) pathway, driving uncontrolled proliferation and survival of melanoma cells. Other important genomic drivers include NRAS and NF1 alterations, as well as changes in PI3K–AKT pathway and cell cycle regulators such as CDKN2A. These molecular features have direct therapeutic implications, particularly the use of BRAF and MEK inhibitors in BRAF‑mutant disease and immune checkpoint inhibitors that target the PD‑1/PD‑L1 and CTLA‑4 pathways.^{[2](https://pubmed.ncbi.nlm.nih.gov/41807883/)[5](https://pubmed.ncbi.nlm.nih.gov/41718747/)}

Clinical Presentation

Melanoma most commonly presents as a pigmented skin lesion with evolving morphology. Classic teaching uses the ABCDE criteria:

• A – Asymmetry: One half of the lesion does not match the other.
• B – Border irregularity: Edges are ragged, notched, or blurred.
• C – Color variation: Shades of brown, black, red, blue, or white within the same lesion.
• D – Diameter: >6 mm is concerning, though smaller lesions can be malignant.
• E – Evolution: Change in size, shape, color, or new symptoms (itching, bleeding, ulceration).

Additional clinical clues include the “ugly duckling” sign (a lesion that looks different from the patient’s other nevi), new pigmented lesions in adulthood, and nodular lesions that may be amelanotic. Subtypes show characteristic patterns: superficial spreading melanoma is often a flat or slightly elevated lesion with variegated pigmentation; nodular melanoma is a rapidly growing dome‑shaped nodule; lentigo maligna melanoma arises on chronically sun‑damaged skin (e.g., face of elderly patients) with a large, irregular macule; acral lentiginous melanoma presents on palms, soles, or nail beds and is more common in people with skin of color.

Non‑cutaneous melanomas may present differently: ocular (uveal) melanoma can cause visual disturbances, floaters, or be incidentally detected on ophthalmologic exam; mucosal melanomas may present with bleeding, mass lesions, or nonspecific symptoms in the oral cavity, anorectum, or genitourinary tract. Ocular and mucosal sites often require specialized imaging and multidisciplinary management due to their unique biology and anatomic constraints.^{[4](https://pubmed.ncbi.nlm.nih.gov/41737198/)}

Diagnosis

Diagnosis begins with a thorough skin examination, including evaluation of all pigmented lesions using dermoscopy where available. Any lesion with concerning features should undergo excisional biopsy with narrow margins to allow accurate histologic assessment. Shave biopsies are generally avoided for suspected invasive melanoma, especially for thicker lesions, because they may underestimate Breslow depth.

Histopathologic evaluation defines key prognostic parameters: Breslow thickness (tumor depth in mm), presence of ulceration, mitotic rate, lymphovascular invasion, and margin status. Clark level is less prognostic than Breslow thickness but may still be reported. Sentinel lymph node biopsy (SLNB) is recommended for staging in patients with intermediate‑thickness melanomas (and selected thin or thick lesions), as nodal status is a major determinant of stage and management.

Staging follows the AJCC TNM system, incorporating tumor thickness, ulceration, nodal involvement, and distant metastases. Imaging (e.g., CT, PET/CT, MRI brain) is indicated for patients with clinically apparent nodal disease, high‑risk primary tumors, or symptoms suggestive of metastasis. Molecular testing for BRAF and other actionable mutations is recommended in advanced or unresectable disease to guide systemic targeted therapies.^{[2](https://europepmc.org/article/MED/41807883)}

Management

Local and Regional Disease

Primary treatment for localized cutaneous melanoma is wide local excision with margins based on Breslow thickness (e.g., 0.5–1 cm for in situ, 1 cm for <1 mm, 1–2 cm for 1–2 mm, and up to 2 cm for thicker lesions, adjusted for anatomic site). SLNB is performed concurrently when indicated for staging.

For stage II–III disease, adjuvant systemic therapy has become standard in many settings to reduce recurrence risk. Options include immune checkpoint inhibitors (e.g., anti‑PD‑1 antibodies) and, in BRAF‑mutant tumors, combinations of BRAF and MEK inhibitors. These therapies exploit the underlying molecular drivers and the immunogenic nature of melanoma.^{[2](https://pubmed.ncbi.nlm.nih.gov/41807883/)[5](https://pubmed.ncbi.nlm.nih.gov/41718747/)}

Advanced and Metastatic Disease

Management of unresectable stage III or stage IV melanoma is driven by tumor burden, performance status, comorbidities, and molecular profile.

• Immune checkpoint inhibitors: Agents targeting PD‑1 (e.g., nivolumab, pembrolizumab) and CTLA‑4 have dramatically improved survival in advanced melanoma by enhancing T‑cell–mediated antitumor responses. Combination regimens can increase response rates at the cost of higher immune‑related toxicity. Natural compounds are being explored as adjunctive immune modulators but remain investigational.^{[5](https://pubmed.ncbi.nlm.nih.gov/41718747/)}
• Targeted therapy: For BRAF V600–mutant melanoma, combinations of BRAF and MEK inhibitors (e.g., dabrafenib plus trametinib, vemurafenib plus cobimetinib) provide rapid and often profound responses. However, resistance is common due to reactivation of MAPK signaling and alternative pathways, prompting investigation of next‑generation targeted strategies and rational combinations.^{[2](https://pubmed.ncbi.nlm.nih.gov/41807883/)}
• Radiation therapy: Used for palliation, local control in oligometastatic disease, or adjuvant treatment in select high‑risk nodal basins, as well as stereotactic radiosurgery for brain metastases.
• Surgery in metastatic disease: Metastasectomy can be considered for isolated or oligometastatic lesions in selected patients, often in conjunction with systemic therapy.

Investigational approaches include oncolytic viruses delivered locally or via biomaterial carriers to enhance intratumoral viral persistence and antitumor immunity, various nano‑formulations (including quercetin‑based strategies) to improve drug delivery and overcome resistance, and exosome‑based targeted therapies particularly relevant to ocular malignancies.^{[1](https://pubmed.ncbi.nlm.nih.gov/41835051/)[3](https://pubmed.ncbi.nlm.nih.gov/41773219/)[4](https://pubmed.ncbi.nlm.nih.gov/41737198/)}

Prevention and Risk Modification

Primary prevention centers on UV avoidance and protection: minimizing midday sun exposure, using broad‑spectrum sunscreen, wearing protective clothing, and avoiding indoor tanning devices. Secondary prevention relies on regular skin self‑examinations, clinical skin checks in high‑risk individuals, and early biopsy of suspicious lesions. Education on recognizing concerning lesions is particularly important in populations with skin of color, where melanoma may present at acral or mucosal sites and be overlooked, leading to delayed diagnosis and poorer outcomes.^{[8](https://europepmc.org/article/MED/41706681)}

Key Clinical Pearls

• Breslow thickness is the single most important prognostic factor in localized melanoma; accurate full‑thickness biopsy is essential.
• Always consider melanoma in any changing pigmented lesion, especially if it is the patient’s “ugly duckling” mole or shows evolution, symptoms, or new onset in adulthood.
• Acral, nail unit, and mucosal melanomas are more frequent in people with skin of color and often present late; maintain a high index of suspicion for non‑sun‑exposed sites.^{[8](https://europepmc.org/article/MED/41706681)}
• BRAF mutation testing is crucial in advanced disease, as it opens the door to targeted BRAF/MEK inhibitor therapy, which can produce rapid clinical responses but is subject to resistance mechanisms requiring ongoing innovation in therapeutic strategies.^{[2](https://europepmc.org/article/MED/41807883)}
• Immune checkpoint inhibitors have transformed melanoma outcomes and are central to management in many stages, including adjuvant and metastatic settings; be vigilant for immune‑related adverse events.
• Emerging modalities such as oncolytic viruses, nanoparticle‑based delivery systems, natural immune‑modulating compounds, and exosome‑based therapies represent promising areas of translational research and may reshape future management paradigms.^{[1](https://pubmed.ncbi.nlm.nih.gov/41835051/)[3](https://pubmed.ncbi.nlm.nih.gov/41773219/)[4](https://pubmed.ncbi.nlm.nih.gov/41737198/)[5](https://pubmed.ncbi.nlm.nih.gov/41718747/)}

Exam Tips for Medical Students

• Know the ABCDE criteria and “ugly duckling” sign for melanoma recognition.
• Remember that wide local excision with appropriate margins is the cornerstone of treatment for localized disease.
• Understand that Breslow thickness, ulceration, and nodal status drive staging and prognosis.
• Be familiar with BRAF‑mutant melanoma and the roles of BRAF/MEK inhibitors and immune checkpoint inhibitors in advanced disease.
• On exams, a rapidly growing, dark or amelanotic nodule that bleeds easily should prompt concern for nodular melanoma, even if ABCDE criteria are not all present.