Premalignant skin lesions

Actinic Keratosis - The Sun's Rough Draft

• Etiology: Chronic UV radiation exposure leading to DNA damage in keratinocytes.
• Presentation: Small, rough, scaly, erythematous papules or plaques. Often described as feeling like "sandpaper."
• Location: Sun-exposed areas like the face, bald scalp, ears, and dorsal hands.
• Histopathology: Basal layer atypia with hyperkeratosis and parakeratosis. Dermis shows solar elastosis.
• Progression: Premalignant lesion with a low but definite risk of transformation into invasive squamous cell carcinoma (SCC).

⭐ The cumulative risk of an individual with multiple actinic keratoses developing an SCC is significantly higher than the risk from a single lesion.

Squamous Cell Carcinoma In Situ - The Confined Cancer

Also known as Bowen's disease, this represents full-thickness epidermal dysplasia without basement membrane invasion. It is a precursor to invasive squamous cell carcinoma (SCC).

• Etiology:
  • UV light exposure (most common)
  • Human Papillomavirus (HPV), esp. types 16, 18
  • Immunosuppression
  • Chronic arsenic exposure
• Clinical Features:
  • Well-demarcated, erythematous, scaly patch or plaque.
  • Can occur on sun-exposed or non-sun-exposed skin.

⭐ On the glans penis or vulva, it is termed Erythroplasia of Queyrat and is strongly associated with HPV.

Dysplastic Nevus - The Rogue Mole

• An atypical mole; a key precursor and risk marker for malignant melanoma. Assessed clinically using the 📌 ABCDE criteria: Asymmetry, irregular Borders, Color variegation, Diameter > 6 mm, and Evolution.

• Histo: Features architectural disorder (asymmetry, rete ridge bridging) and cytologic atypia (irregular, hyperchromatic nuclei, nuclear enlargement). Lamellar fibroplasia is common.

• Genetics: Associated with germline mutations in the CDKN2A gene on chromosome 9p21, particularly in Familial Atypical Mole and Melanoma (FAMM) syndrome.

• Management: Biopsy suspicious lesions. Regular, lifelong skin surveillance is crucial for high-risk individuals.

⭐ The presence of multiple dysplastic nevi (>5) can increase the relative risk of developing melanoma by more than 10-fold compared to the general population.

Lentigo Maligna - The Slow Shadow

• A specific subtype of melanoma in situ.
• Epidemiology: Typically affects the elderly on chronically sun-damaged skin, especially the face, ears, and neck.
• Clinical: Presents as a large, slowly enlarging, flat macule (patch) with irregular borders and variable pigmentation (tan to black).
• Histology: Shows a proliferation of atypical melanocytes confined to the basal layer of the epidermis, often with adnexal extension.
• Progression: Has a low but definite risk (~5%) of evolving into invasive lentigo maligna melanoma over decades.

⭐ High-Yield: Characterized by a prolonged radial (horizontal) growth phase, often lasting for years to decades, before any potential vertical invasion into the dermis.

High-Yield Points - ⚡ Biggest Takeaways

• Actinic keratosis is the most common precursor to squamous cell carcinoma (SCC), feeling like sandpaper on sun-exposed skin.
• Bowen's disease is SCC in situ, defined by full-thickness epidermal atypia without dermal invasion.
• Keratoacanthoma, a rapidly-growing crateriform nodule, is treated as well-differentiated SCC despite potential regression.
• Dysplastic nevi are atypical moles indicating increased lifetime risk for malignant melanoma.
• Lentigo maligna is melanoma in situ, presenting as a flat macule on sun-damaged skin.