A 72-year-old woman with a history of multiple solar keratoses presents with a 2 cm erythematous, scaly plaque on the forehead that has been present for 2 years. The lesion is flat with ill-defined borders and does not ulcerate. On dermoscopy, there is a homogeneous erythematous area with fine scaling. Biopsy reveals basaloid cells in the superficial dermis with a broad, pushing border. What is the most likely subtype of basal cell carcinoma?

## Basal Cell Carcinoma Subtype Classification ### Clinical Presentation Analysis **Key Point:** The flat, scaly erythematous plaque with ill-defined borders and superficial dermal involvement on histology is diagnostic of superficial BCC, the second most common subtype. ### Histopathologic Correlation | BCC Subtype | Histology | Clinical Features | Prognosis | |-------------|-----------|-------------------|----------| | **Nodular** | Well-demarcated nodules; peripheral palisading | Pearly nodule; central ulceration; rolled edges | Good; low recurrence | | **Superficial** | Buds of basaloid cells in superficial dermis; broad pushing border | Flat erythematous plaque; ill-defined borders; scaly | Good; low recurrence if completely treated | | **Infiltrative** | Thin strands and nests; infiltrative border | Ill-defined; indurated; scar-like; may ulcerate | Guarded; higher recurrence rate | | **Basosquamous** | Basaloid cells with squamous differentiation | Aggressive; nodular or ulcerated; rapid growth | Poor; high recurrence and metastasis risk | ### Superficial BCC: Key Features **High-Yield:** Superficial BCC accounts for ~15–20% of all BCCs and is characterized by: 1. **Clinical presentation:** - Flat or slightly raised erythematous plaque - Ill-defined borders (unlike nodular BCC) - Fine scaling or crusting - Often multiple lesions - Commonly on trunk 2. **Histopathology:** - Buds and strands of basaloid cells arising from basal layer - Confined to superficial dermis - Broad, pushing (non-infiltrative) border - Retraction artifact present - No central ulceration 3. **Dermoscopy:** - Homogeneous erythematous area - Fine scaling - Lack of arborizing vessels (unlike nodular BCC) - Pearly appearance may be absent **Clinical Pearl:** Superficial BCC can mimic inflammatory dermatoses (eczema, psoriasis, contact dermatitis) clinically, making biopsy essential for diagnosis. ### Differential Diagnosis of BCC Subtypes ```mermaid flowchart TD A[Suspected BCC]:::outcome --> B{Clinical morphology?}:::decision B -->|Pearly nodule + ulceration| C[Nodular BCC]:::outcome B -->|Flat plaque + ill-defined| D[Superficial BCC]:::outcome B -->|Scar-like + indurated| E[Infiltrative BCC]:::outcome B -->|Aggressive + rapid| F[Basosquamous BCC]:::urgent C --> G[Histology: well-demarcated nodules]:::action D --> H[Histology: superficial buds, pushing border]:::action E --> I[Histology: thin infiltrative strands]:::action F --> J[Histology: basaloid + squamous differentiation]:::action ``` ### Why This Case Is Superficial BCC 1. **Flat, scaly plaque** — not a nodule 2. **Ill-defined borders** — characteristic of superficial type 3. **2-year duration** — slow growth typical of superficial BCC 4. **Histology: superficial dermal involvement with broad, pushing border** — pathognomonic for superficial subtype 5. **No ulceration** — distinguishes from nodular BCC **Mnemonic: BCC Subtype Recognition** - **N**odular = **N**odule, **N**ecrosis (ulceration) - **S**uperficial = **S**caly plaque, **S**uperficial dermis - **I**nfiltrative = **I**ll-defined, **I**ndurated (scar-like) - **B**asosquamous = **B**ad prognosis, **B**oth cell types ### Treatment Implications - Superficial BCC: Responds well to topical imiquimod, 5-FU, or photodynamic therapy - Nodular BCC: Requires surgical excision - Infiltrative BCC: Mohs micrographic surgery preferred due to higher recurrence - Basosquamous BCC: Aggressive; wide excision or Mohs surgery mandatory [cite:Robbins 10e Ch 25]