What is the recent classification of basal cell carcinoma (BCC) clinically and pathologically?

Recent Classification of Basal Cell Carcinoma

Basal cell carcinoma is currently classified into two primary risk categories—low-risk and high-risk—based on clinical features, anatomic location, and histopathologic subtype, with this stratification directly determining treatment approach and prognosis. 1, 2

Clinical Classification

Low-Risk BCC Features

• Well-defined clinical borders with nodular or superficial morphology 2
• Primary tumors (not recurrent) 2
• Small size: <20 mm in low-risk anatomic locations (Area L) or <10 mm in moderate-risk locations (Area M) 2
• Nodular variant: Most common presentation, appearing as a pearly, translucent papule or nodule, often with telangiectasias 3, 4
• Superficial variant: Presents as erythematous, scaly patches, typically on the trunk 3, 4

High-Risk BCC Features

• Location in Area H (central face, eyelids, eyebrows, periorbital skin, nose, lips, chin, mandible, ears) regardless of size 1, 2
• Poorly defined clinical margins suggesting subclinical extension 1, 2
• Recurrent tumors after previous treatment 1, 2
• Large size: ≥20 mm in Area L or ≥10 mm in Area M 2
• Morpheiform (sclerosing) variant: Appears as indurated, scar-like plaques with ill-defined borders and deceptively small clinical appearance despite extensive subclinical extension 5, 3
• Pigmented variant: Contains melanin, may mimic melanoma clinically 3, 4

Histopathologic Classification

Low-Risk (Indolent) Histologic Subtypes

• Nodular BCC: Most common subtype, characterized by well-circumscribed nests of basaloid cells with peripheral palisading 6, 3
• Superficial BCC: Buds of basaloid cells attached to the epidermis, confined to papillary dermis 6, 3
• Pigmented BCC: Nodular pattern with melanin pigmentation 6
• Infundibulocystic BCC: Shows follicular differentiation 6
• Fibroepithelioma of Pinkus: Rare variant with anastomosing strands of basaloid cells in fibrous stroma 3, 4

High-Risk (Aggressive) Histologic Subtypes

• Infiltrative BCC: Irregular, finger-like projections extending into dermis with extensive subclinical spread 5, 6, 3
• Micronodular BCC: Small, discrete nests of tumor cells scattered throughout dermis 6, 3
• Morpheiform (sclerosing) BCC: Thin strands of tumor cells embedded in dense fibrous stroma, highly infiltrative 6, 3
• Basosquamous carcinoma: Mixed features of BCC and squamous cell carcinoma with higher metastatic potential than typical BCC and must be managed as squamous cell carcinoma 2, 7

Additional High-Risk Histopathologic Features

• Perineural invasion: Tumor tracking along nerve sheaths 1, 2, 6
• Invasion beyond reticular dermis into subcutaneous tissue 1, 2
• Perivascular invasion 5

Critical Diagnostic Considerations

Biopsy Requirements

• Punch biopsy or deep shave biopsy extending into reticular dermis is mandatory to detect infiltrative components that may be present only at deeper margins 5, 2
• Superficial tangential biopsies frequently miss aggressive subtypes and should never be performed 2
• Multiple scouting biopsies may be needed when recurrent tumor, deep invasion, or aggressive features are suspected 1, 5

Mixed Histology Pitfall

• 43% of BCCs demonstrate mixed histology with more than one pathologic pattern 8
• Only 10% of biopsy reports identify mixed histology, meaning aggressive components are frequently missed on initial biopsy 8
• This represents a major cause of recurrence when superficial biopsy identifies only the nonaggressive component while missing the deeper aggressive subtype 8

Essential Pathology Report Elements

The pathology report must include 1, 2:

• Specific histologic subtype(s) present
• Invasion beyond reticular dermis if present
• Perineural invasion if detected
• Notation if tumor extends to biopsy base (deeper invasion cannot be ruled out)
• Margin status for excisional specimens

Risk Compounding Factors

Additional features that elevate risk regardless of subtype 5, 2, 7:

• Immunosuppression (transplant recipients, chronic immunosuppressive therapy)
• Prior radiation therapy to the site
• Rapid growth of the lesion
• Neurologic symptoms suggesting perineural involvement

Treatment Implications Based on Classification

Low-Risk BCC

• Surgical excision with 4-mm clinical margins and histologic margin assessment 2
• Curettage and electrodessication may be considered for low-risk tumors in non-terminal hair-bearing locations 1
• Topical imiquimod achieves 75% composite clearance for superficial BCC ≤2 cm diameter 9

High-Risk BCC

• Mohs micrographic surgery is the treatment of choice, achieving 5-year disease-free rates exceeding 98% 5, 2
• Complete margin assessment is crucial—treatment without margin control leads to high recurrence rates 2
• Infiltrative BCC is classified as high-risk based on histologic subtype alone, regardless of size or location 5