Benign Skin Tumours

Seborrhoeic Keratosis

•    "Stuck-on," waxy or verrucous appearance

•    Varying colour (brown to black)

•    Common in elderly ("barnacles of aging")

•    Sign of Leser–Trélat: sudden onset of multiple lesions → may indicate internal malignancy (esp. GI)

Dermatofibroma

•    Firm, hyperpigmented nodules, often on lower limbs

•    Dimple sign: central depression on pinching

•    Usually asymptomatic; no malignant potential

Lipoma

•    Soft, mobile, painless subcutaneous mass

•    Common on trunk, shoulders

•    Composed of mature adipocytes

Pre-Malignant Lesions

Actinic (Solar) Keratosis

•    Rough, scaly erythematous plaques

•    Sun-exposed areas (scalp, face, forearms)

•    Risk of progression to squamous cell carcinoma (~1%)

Bowen’s Disease (SCC in situ)

•    Well-defined, erythematous scaly plaque

•    Full-thickness epidermal dysplasia, no dermal invasion

•    Common on sun-exposed skin, can progress to invasive SCC

Malignant Skin Tumours

Basal Cell Carcinoma (BCC)

•    Most common skin cancer, locally invasive, rarely metastasises

•    "Pearly" or translucent nodule with rolled edge, central ulceration ("rodent ulcer"), telangiectasia

•    Risk factors: UV exposure, fair skin, immunosuppression (e.g., post-transplant)

•    Subtypes: nodular (most common), superficial, morphoeic

Treatment

•    Surgical excision with margin

•    Mohs micrographic surgery (facial lesions)

•    Topical treatments (imiquimod, 5-FU) for superficial BCC

Squamous Cell Carcinoma (SCC)

•    Hyperkeratotic, crusted, or ulcerated nodule

•    Arises from actinic keratosis or chronic wounds (Marjolin’s ulcer)

•    Higher metastatic potential than BCC (but still low overall)

Risk factors

•    UV exposure, chronic inflammation (e.g., ulcers, scars)

•    Immunosuppression (e.g., transplant patients → up to 100× risk)

•    HPV infection (anogenital SCC)

Treatment

•    Surgical excision with margin

•    Radiotherapy (alternative in inoperable cases)

Malignant Melanoma

•    Arises from melanocytes

•    ABCDE criteria:

o    A: Asymmetry

o    B: Border irregular

o    C: Colour variation

o    D: Diameter >6 mm

o    E: Evolution (changing)

Types

•    Superficial spreading: most common, horizontal growth phase

•    Nodular: rapid vertical growth, poorer prognosis

•    Lentigo maligna: slow-growing, sun-exposed elderly skin

•    Acral lentiginous: palms, soles, subungual; more common in darker skin types

Prognostic factors

•    Breslow thickness (most important for prognosis)

•    Ulceration, mitotic rate, lymphovascular invasion

Treatment

•    Wide local excision

•    Sentinel lymph node biopsy for staging

Other Malignant Skin Tumours

Merkel Cell Carcinoma

•    Rare, aggressive neuroendocrine tumour

•    Red–violaceous rapidly growing nodule, sun-exposed areas

•    Often in elderly or immunosuppressed

•    High rate of local recurrence and metastasis

Cutaneous Lymphomas

•    Most common: Mycosis fungoides (cutaneous T-cell lymphoma)

•    Presents as scaly patches → plaques → tumours

•    Sézary syndrome: erythroderma, circulating malignant T cells (Sézary cells)

Extra Revision Pearls

•    Chronic ulcer or burn scar → SCC (Marjolin’s ulcer)

•    Multiple rapidly growing keratoacanthomas → think Muir–Torre syndrome (subset of Lynch)

•    Melanoma staging relies heavily on Breslow depth

•    Immunosuppressed patients → SCC risk dramatically increased