L12 - Skin pathology: melanoma, how detecting the BRAF mutation changed the prognosis (Dr Francesca Maggiani) Flashcards
- Reviewing the histology of the skin - Understanding the pathogenesis and the histology of melanocytic tumours - Describing the genetics abnormalities associated with melanocytic tumours - Explaining the new treatments linked to the BRAF status
What is meant by a melanocytic tumour?
A melanocytic tumour refers to a tumour originating from melanocytes, the pigment-producing cells. The majority of these tumours are cutaneous melanomas, meaning they occur on the skin.
Can melanocytic tumours occur outside the skin?
Yes, melanocytic tumours can also occur outside the skin, such as in the mucosa and the meningeal system (the membranes surrounding the brain and spinal cord).
What are the key areas covered when studying melanocytic tumours?
- Histology of the skin – Understanding skin structure.
- Pathogenesis – How melanocytic tumours develop.
- Morphological and genetic abnormalities – Linking structural changes to genetic mutations.
- Treatment advances – Using genetic discoveries to improve therapy and prognosis.
What is the largest organ in the human body?
The skin is the largest organ covering ~ 2 square metres of surface area
What are the three main layers of the skin
- Epidermis - the oytermost layer, made of epithelial cells
- Dermis - A fibrous tissue layer containing glands, hair follicles, blood vessels, lymphatics and nerves
- Hypodermis (subcutis) - the deeper layer, made up of adipose (fat) tissue
What structures are found within the dermis
The dermis contains:
- Adnexal structures (sweat glands, sebaceous glands, and hair follicles).
- Blood vessels & lymphatics (for circulation and immune function).
- Nerves (for sensation).
- Elastic fibres & collagen (for skin texture and flexibility).
How does skin thickness vary across the body?
Varries a lot
What parts of the body have the thinnest vs the thickest skin
Thinnest skin = around the eyes ( ~0.5mm thick)
thickest skin = on the planter (sole) surface of the foot ( over 1mm)
How does skin structure vary across different body regions?
- Some areas are hair-bearing, while others are not.
- Different regions have varying densities of sweat and sebaceous glands.
- Skin thickness varies significantly depending on the location.
What is the stratum corneum and what is its function
The stratum corneum is the outermost layer of the epidermis, composed of dead cells without nuclei. These cells are held together by tight junctions and provide a protective barrier. It is also the layer that can be scrubbed off.
What are the 3 main layers of the epidermis? (not skin - different question)
1 Stratum corneum – Dead, keratinized cells providing protection.
2. Upper layers – Flattened epithelial cells.
3. Basal layer (stratum basale) – Small, round cells that divide and renew the skin.
What type of epithelium makes up the epidermis?
The epidermis is composed of keratinized stratified squamous epithelium.
What does stratified squamous epithelium mean
Stratified squamous means it has multiple layers of cells.
What does keratinised epithelium mean
Keratinized means the top layer is covered with dead cells that provide extra protection.
How does the epithelium of the skin differ from the mucosa?
Both have stratified squamous epithelium, but:
Skin is keratinized, meaning it has a protective dead cell layer on top.
Mucosa (e.g., oral cavity) lacks keratinization and is softer.
How often is the epidermis completely renewed?
The epidermis undergoes constant turnover and is fully replaced every 2 to 4 weeks.
What influences the rate of epidermal renewal?
- External insults (e.g., UV exposure, mechanical damage).
- Body location (areas exposed to friction renew faster).
What are the main functons of the skin?
- Protection - Shields against mechanical, thermal, chemical, chemical stresses as well as dehydation invasion by micro organisms and UV damage
- Sensation - Contains nerve receptors for touch, pressure, pain and temperature
- Thermoregulation - Regulates body temperature through sweat production, hair, adipose tussue and pilorector muscle contraction
- Metabolic functions - Subcutanous adipose tissue is involved in the production of vitamin D and triglycerides
What is vitamin D crucial for?
Calcium metabolism
How does the skin protect against environmental damage?
Acts as a barrier against
1. Mechanical stress e.g. friction and trauma
2. Chemical exposure e.g. Irritants and toxins
3. Ultraviolet radiation e.g. Prevents DNA damage
How does the skin contribute to thermoregulation
Sweating: Increases heat loss when the body is too hot.
adipose tissue
Piloerector muscles: Contract to make hair stand, trapping warmth in cold conditions.
What sensory functions does the skin have
- touch
- Pressure
- Pain
- Temperature changes
What metabolic function does the skin perform
- Promotes calcium absorption in the gut.
- Prevents excessive calcium loss in urine.
- Essential for bone calcification and strength.
What happens if the body lacks vitamin D?
Vitamin D deficiency leads to poor bone mineralization, resulting in:
- Rickets (in children) – Soft, weak bones prone to deformities.
- Osteomalacia (in adults) – Fragile bones that break easily.
Why do people with darker skin need more sunlight for vitamin D activation?
- Darker skin has more melanin, which blocks UV light from reaching vitamin D precursors.
- This reduces vitamin D activation, requiring more sun exposure.
- In places with less sunlight (e.g., UK in winter), supplementation is recommended, especially for darker-skinned individuals.
What are the three types of ultraviolet (UV) radiation?
- UVA : penetrates deep into the dermis affecting collagen and elastic fibers
- UVB - Absorbed by the epidermis, responsible for vitamin D activation and potential melanocyte damage
- UVC - Filtered by ozone layer and does not reach the skin
Which type of UV radiation affects the dermis and causes changes in collagen and elastic fibers
UVA penetrates deeply into the dermis leading to changes in collagen and elastic fibers
Which type of UV radiation is absorbed by the epidermis and plays a role in vitamin D activation
UVB is absorbed in the epidermis where it helps activate vitamin D but it can also cause damage to melanocytes increasing the risk of melanocytic lesions and skin cancer
What determines skin tone and UV protection?
Skin tone is influenced by melanin production:
- Eumelanin – Brownish-black pigment, provides better UV protection ( rarer burns and skin cancers)
- Pheomelanin – Reddish-yellow pigment, less effective against UV exposure ( burns more regularly and higher risk of skin cancer)
Why are individuals with red or blonde hair more vulnerable to sun damage?
They have more pheomelanin, which is less effective at protecting against UV exposure. This makes them:
More likely to burn instead of tan.
At higher risk of skin cancer.
How does melanoma risk differ between lighter and darker-skinned individuals?
Lighter skin: Higher risk of melanoma, usually in sun-exposed areas.
Darker skin: Lower melanoma incidence, but when it occurs, it is often in less visible locations (e.g., hands, feet) and diagnosed at a later stage.
Why is melanoma diagnosis often delayed in darker-skinned individuals?
- Melanomas occur in less common areas (e.g., palms, soles, nails).
- They are harder to spot, leading to late diagnosis and worse prognosis
How did Bob Marley die of melanoma, and why was it misdiagnosed?
He had acral lentiginous melanoma on his toe which was mistaken for a sports injury, delaying diagnosis.
By the time it was correctly identified, it was advanced and had spread.
where does acral lentiginous melanoma (ALM) occur
ALM occurs on hairless skin (e.g., under nails, soles of feet, palms of hands).
how does acral lentiginous melanoma (ALM) differ from other melanomas?
Unlike most melanomas, which are caused by UV exposure, ALM is more strongly linked to genetic factors. Although is rare overall, but it is the most common form of melanoma in people of color.
Where is melanoma most common worldwide,
- Melanoma is more frequent in predominantly Caucasian populations and areas with high sun exposure.
- Australia has the highest incidence of skin cancer globally due to a large Caucasian population exposed to intense sunlight.
why is melanoma incidence increasing in the UK
- Air travel and holiday sun exposure have increased skin cancer rates in places like the UK since the 1970s.
How common is skin cancer in Australia?
- Australia has 2-3 times the skin cancer rates of Canada, the US, and the UK.
- 2 in 3 Australians will be diagnosed with skin cancer by age 70.
- Over 750,000 people are treated for non-melanoma skin cancers each year.
- In 2014, 13,134 Australians were diagnosed with melanoma.
What is the primary cause of skin cancer?
- The majority of skin cancers are caused by exposure to the sun (UV radiation).
- Some genetic conditions, like retinoblastoma syndrome, can also increase the risk.
What areas of the body are most affected by skin cancer?
Sun-exposed areas are most commonly affected e.g. hands, arms, face, chest ( especially in men)
What is the ABCD rule for detecting melanoma?
The ABCD rule can be used by health professionals and patients to check for the
main warning signs of melanoma
What does ABCD in the ABCD rule stand for
A = Asymmetry – Two halves of the mole look different in shape or color.
B = Border – Irregular, jagged, notched, or blurred edges.
C = Color – Multiple colours, uneven shading, or a different colour than other moles.
D = Dimensions (changing size) – Growth outwards (flat lesion) or upwards (hard lump), or both.
What is the EFG rule for detecting melanoma
Nodular melanoma may lack the signs referred to for the ABCD signs so EFG can be used instead
What does EFG stand for in the EFG rule
- E = Elevationm - raused above the skin level
- F = Firmness to touch- feels solid or hard to touch
- G = Growth. Persistent growth for over one month
Why is monitoring moles important?
- Benign moles (nevi) tend to be symmetrical, have regular borders, and remain stable in size and color.
- Warning signs include asymmetry, irregular edges, color changes, growth, firmness, or elevation.
- Some melanomas shrink due to an inflammatory response, making them harder to detect.
- Any suspicious melanocytic lesion should be excised and examined microscopically.
What percentage of melanomas occur de novo (without a previous pigmented lesion)?
70% of melanomas occur de novo, meaning they develop without any previous pigmented lesions.
What is the trend in the incidence of malignant melanoma? (since the 1990s)
The incidence of malignant melanoma has increased by 139% since the 1990s
25% of malignant melanomas occur in what age group
those over 75 years of age
How do darker skin types typically present with melanoma?
People with darker skin types are more likely to develop acral and subungual melanoma (on the palms, soles, or under nails).
what does the clark model describe
The Clark model describes the sequence of histological changes in melanoma
What is the progression of malignant melanoma according to the Clark model?
- Nevus – Clusters of melanocytes that are well-formed and do not spread into the epidermis.
- Dysplastic nevus – Atypical melanocytes with random, discontinuous changes.
- Radial growth phase (RGP) – Cells proliferate within the epidermis.
- Vertical growth phase (VGP) – Cells penetrate the basal membrane and invade the dermis.
- Metastatic melanoma – The tumor spreads to other parts of the body.
How does melanoma appear differently on hands and feet, especially in darker-skinned individuals?
they can appear as dark, thick lesions which can easily be mistaken for hemorrhages or bruising. this is why early detection and proper evaluation are critical
How do melanocytic lesions progress in terms of changes in their histology?
BRAF mutations are frequently involved in early development of melanocytic lesions.
However, other genetic factors are needed for the tumor to develop into malignant melanoma.3
What does a typical benign nevus look like at the histological level?
melanocytes are clustered in the epidermal junction (between the epidermis and the dermis). These cells do not invade the higher layers of the epidermis and there is no pleomorphism ( variation in cell shape or size ) or atypical features
What are the features that suggest a malignant melanoma in sity (localised melanoma)?
- In situ melanoma typically shows melanocytes at the epidermal junction without deeper invasion into the dermis.
- Features of stagitoid spread (individual melanocytes migrating upwards into the epidermis) may also appear.
- You may see atypical melanocytes that are paler and exhibit cellular atypia (irregular cell structure).
- There could be fusion of papillae, where the epidermal papillae should be separate but instead are joined together.
What are signs of invasive melanoma at the histological level?
- may see melanocytes invading deeper into the dermis
- Melanin appears as brown pigment throughout the tissue
- There could still be nesting of melanocytes in the epidermal junction, but the cells are also penetrating deeper into the dermis
Why is it important to measure the depth of invasion in melanoma?
- The depth of invasion is critical for prognosis and staging of melanoma.
- This measurement helps determine how far the melanoma has spread into the skin layers and provides important information about its potential to metastasize.
How can metastatic melanoma be confused with primary melanoma?
If melanoma is only seen in the dermis and not in the epidermis, it may raise suspicion that the lesion is metastatic melanoma rather than a primary one
how can metastatic melanoma present
Metastatic melanoma can present as nodules or lumps in the skin, sometimes appearing years after a previous excision of a pigmented lesion.
what do histological examination and immunohistochemistry for melanocytic markers help distinguish
between primary melanoma and metastasis
What role does immunohistochemistry play in diagnosing melanoma?
- Immunohistochemistry using melanocytic markers (e.g., S100, HMB-45) helps confirm melanoma.
- Positive staining for melanocytic markers indicates that the lesion is a melanocytic lesion, and the cells may extend higher up in the epidermis, suggesting malignant behavior.
What are the four major subtypes of invasive melanoma?
- Acral lentiginous melanoma
- Lentigo maligna melanoma
- Nodular melanoma
- Superficial spreading melanoma
What are helpful features that differentiate melanoma from benign lesions?
- Asymmetry of the lesion.
- Atypia in melanocytes.
- Band-like chronic inflammatory infiltrate in the dermis.
- Lack of maturation in dermal tumor cells.
- Lateral extension of individual melanocytes.
- Melanocytes with clear cytoplasm and finely dispersed chromatin.
- Mitotic figures in melanocytes, especially atypical ones.
- Pleomorphism (variation in shape/size) of tumor cells.
- Poor circumscription of intraepidermal component.
- Presence of chromosomal gains or losses.
- Transepidermal migration of melanocytes.
What histopathological features are assessed to predict the prognosis of melanoma?
- Lack of maturation in dermal tumor cells.
- Lateral extension of melanocytes.
- Atypia and mitotic activity.
- Inflammatory infiltrate presence.
- Thickness of the lesion (measured by Breslow and Clark’s levels).
- Ulceration, which is a strong predictor of survival.
- Microsatellite lesions, indicating lymphatic sprea
What is the difference between Breslow and Clark’s levels for measuring melanoma?
- Clark’s levels: Measure the depth of the tumor in the dermis (superficial dermis, deep dermis, etc.).
- Breslow thickness: Measures the millimeters of tumor extension, providing an estimate of how deep the tumor has invaded. This is a key predictor for potential lymphatic invasion.
Why is ulceration a strong predictor in melanoma prognosis?
Ulceration indicates a more aggressive tumor and poor prognosis.
It is part of the TNM staging system and plays a critical role in survival prediction.
What are the potential pitfalls when assessing microsatellites in melanoma?
- Microsatellites may indicate lymphatic spread but can be challenging to identify due to the 2D nature of tissue slides.
- It may be difficult to distinguish normal dermis from tumor tissue, leading to potential overcalling of linked tumor areas.
How does microsatellite spread affect melanoma prognosis
The presence of microsatellites suggests that melanoma cells have spread through the lymphatic system, which can indicate a poor prognosis and increased risk of metastasis.
What is microsatellite spread
The presence of small clusters of cancer cells (microsatellites) located near the primary tumour site but separate from it ( indicates that the cancer has spread)
What is the strongest predictor of survival in melanoma?
Lymph node metastasis is the strongest predictor of survival, though it is not always available in diagnosis.
Why is regression in melanoma a poor prognostic indicator?
- Regression occurs when the tumor appears smaller due to destruction by immune cells, but the tumor’s original thickness still negatively affects prognosis.
why is it difficult to assess the trye depth of the melanoma
Because of features like fibrosis, inflammation and little vessels
Why are margins important in melanoma prognosis?
Wider margins during excision reduce the risk of local recurrence.
Ensuring all tumor tissue is removed is crucial for preventing melanoma regrowth.
What are the main genetic pathways involved in melanoma development?
- RAS-RAF-MEK-ERK Pathway (BRAF, NRAS, KIT) → Proliferation & evasion of apoptosis
- p16(INK4A)-CDK4-RB Pathway → Evasion of cellular senescence
- ARF-p53 Pathway → Inactivation of DNA damage response & evasion of senescence
- PI3K-AKT Pathway (PTEN, PIK3CA) → Invasion & metastasis
What percentage of familial melanoma cases are associated with mutations in the CDKN2A locus?
About 20% of melanoma-prone families have a point mutation in the CDKN2A locus at 9p21, which encodes p16(INK4a) and p14(ARF).
What is the significance of microsatellite instability in melanoma?
- Microsatellite instability is more common in pediatric melanoma (43%) than in adult melanoma (30%).
- It is also present in nevi (9%).
- This instability can indicate a genetic predisposition to melanoma and is associated with specific mutations.
What are the key features pathologists assess in melanoma for prognosis?
- Depth of invasion (Breslow thickness).
- Lymph node metastasis (strongest survival indicator).
- Regression (poor prognosis).
- Margins for excision.
- Genetic mutations in the RAS-RAF, p16/CDK4, and ARF-p53 pathways.
- Microsatellite instability and chromosomal gains/losses.
What role do chromosomal changes play in melanoma?
Most melanomas show multiple chromosomal gains and losses, which differentiate them from benign nevi, which lack chromosomal alterations.
These changes can be part of the final stages of melanoma development, contributing to malignancy.
How does the BRAF mutation relate to melanoma?
The BRAF mutation is a key early event in melanoma initiation but requires additional mutations for the tumor to become malignant.
what percentage of melanomas have a BRAF mutation
50% of melanomas (and many benign nevi)
What does BRAF do
Activates the RAS-RAF-MEK-ERK pathway where it promotes prolferation and evades apoptosis
is a mutation in BRAF sufficient alone for malignant transforamation
No
How does p16(INK4A) loss contribute to melanoma?
p16(INK4A) normally inhibits CDK4/6 to prevent uncontrolled cell cycle progression. Without it you get Rb hyperphosphorylation which results in uncontrolled cell devision ( evasion of cellular senescence)
What is often lost in familial melanoma cases
p16
What is the function of TP53
TP53 regulates DNA damage repair and apoptosis
what does a mutation in TP53 lead to
Inactivation of the DNA damage response, evasion of apoptosis and cellular senescence (often inactivated in aggressive melanomas)
How does PTEN loss contribute to melanoma progression
PTEN normally inhibits PI3K-AKT signaling. When lost there is increased PI3K-AKT activation which leads to invasion and metastasis
What is the primary goal of targeted therapy in metastatic melanoma?
To target specific genetic mutations (e.g., BRAF, MEK, C-KIT) that drive melanoma growth and improve survival rates.
Which gene mutation is most commonly targeted in melanoma treatmemt
BRAF gene mutations ( especially BRAF V6ppE) are present in ~50% of melanomas and are a major target for therapy
How do BRAF inhibitors work
BRAF inhibitors block the mutated BRAF protein, preventing excessive cell growth
what are example BRAF inhibitors
- Vemurafenib
- Dabrafenib
- LGX818
Wy are MEK inhibitors often used alongside BRAF inhibitors
MEK inhibitors prevent resistance by blocking the next step in the pathway, leading to better tumor shrinkage and longer survival
what are examples of MEK inhibitors which are used alongside BRAF inhibitors
- Trametinib
- Cobimetinib
- Selumetinib
What is the benefit of combining BRAF and MEK inhibitors
Combination therapy significantly increases response rates, delays resistance and improves overall survival compared to BRAF inhibitors alone
What is the role of C-KIT inhibitors in melanoma
C-KIT inhibitors target melanomas with C-KIT mutations
which melanomas typically have C-KIT mutations
- Acral melanomas (palms, soles, nails)
- Mucosal melanomas
- Chronic sun damaged skin melanomes
what are examples of C-KIT inhibitors
Imatinib (Gleevec)
Dasatinib (Sprycel)
Nilotinib (Tasigna)
What are other gene target inhibitors currently under clinical trial
Axitinib (Inlyta) – VEGF inhibitor
Pazopanib (Votrient) – VEGF and PDGFR inhibitor
Everolimus (Afinitor) – mTOR inhibitor
How has targeted therapy changed the prognosis of metastatic melanoma?
Before targeted therapy, metastatic melanoma had an extremely poor prognosis.
✅ With BRAF/MEK inhibitors, survival rates significantly improved.
✅ Combination therapy + immunotherapy further enhances survival.
What were the results of the COMBI-AD trial for Stage III melanoma?
📋 Dabrafenib + Trametinib vs. Placebo
Time RFS (Dabrafenib + Trametinib) RFS (Placebo)
1-Year 88% 56%
2-Year 67% 44%
3-Year 59% 40%
4-Year 54% 38%
✅ Survival improved significantly with targeted therapy.
Why is metastatic melanoma no longer a “death sentence”?
Targeted therapy + immunotherapy has transformed treatment, extending survival and improving quality of life.
