Basal Cell Carcinoma (BCC)

Overview

Pathogenesis

• In sporadic BCC, PTCH1 mutations bear the signature of UV-induced DNA damage (C→T transitions at dipyrimidine sites).
• In Gorlin syndrome (Nevoid BCC Syndrome - NBCCS), germline PTCH1 mutations cause familial BCC along with odontogenic keratocystic tumors and medulloblastoma.
• Acquired TP53 mutations (also UV-induced) are common in both familial and sporadic forms.

• Without SHH ligand: PTCH inhibits SMO → no tumor growth
• With SHH binding or PTCH mutation: SMO is released → GLI activation → unregulated mitosis
• Robbins & Kumar Basic Pathology, p. 3259; Fischer's Mastery of Surgery 8e, p. 1887

Clinical Subtypes

Figure: A - Superficial BCC (forearm). B - Nodular, ulcerated BCC (right nasal ala). C - Morpheaform BCC with scar-like appearance.

• Harrison's Principles of Internal Medicine 22e, p. 650; Fischer's Mastery of Surgery 8e, p. 1888

Histopathology

• Nests and cords of basaloid cells with hyperchromatic nuclei, scant cytoplasm, and high nuclear-to-cytoplasmic ratio
• Peripheral nuclear palisading - the outermost cells of the tumor nests align in a row
• Stromal clefting (retraction artifact) - characteristic gap between tumor cell nests and surrounding stroma (distinguishes BCC from trichoblastoma, where clefting occurs within the stroma)
• Mucinous or fibrotic stroma
• Absent on mucosal surfaces (only arises from epidermis or follicular epithelium)

Figure: A - Classic nodular BCC on sun-damaged skin. B - Dermoscopy showing central erosion and gray globular structures (melanophages). C - Confocal microscopy showing dermal basaloid nests (asterisks) with cleft formation.

Risk Factors

• Cumulative UV/sun exposure (primary risk factor)
• Light skin (Fitzpatrick types I-II)
• Increasing age
• Male sex
• Immunosuppression (organ transplant recipients, HIV)
• History of prior radiation
• Genetic syndromes: Gorlin syndrome, xeroderma pigmentosum, Bazex syndrome
• Arsenic exposure

High-Risk Features (Predicting Recurrence)

• Fischer's Mastery of Surgery 8e, p. 1888-1889

Treatment

Surgical (Preferred for High-Risk BCC)

• Gold standard for high-risk BCC (H-zone, large, recurrent, poorly defined margins, high-risk histology)
• Serial intraoperative frozen section analysis of 100% of the surgical margin
• 5-year recurrence rate: ~1-4% for primary BCC, 4-8% for recurrent BCC
• 99.4% cure rate for primary eyelid BCC (Mohs' own series of 1,124 patients)
• Meta-analysis of >10,000 patients: 5-year recurrence 3% (Mohs) vs. 5% (standard excision)

• Adequate for low-risk BCC with standard margins (4 mm for nodular BCC)
• Infiltrative/micronodular subtypes may need 5-10 mm margins for clearance

Non-Surgical Options (Generally for Low-Risk BCC)

• Fischer's Mastery of Surgery 8e, pp. 1889-1892

Systemic Therapy (For Locally Advanced or Metastatic BCC)

• Vismodegib (FDA-approved for locally advanced AND metastatic BCC) - small molecule SMO inhibitor
• Sonidegib (FDA-approved for locally advanced BCC only)
• Both block SMO, downstream of the PTCH1/Hh pathway
• Mutation testing NOT required (virtually all BCC have aberrant Hh signaling)
• ERIVANCE trial (vismodegib): Objective response rate 60% (locally advanced), 49% (metastatic); duration ~1.5-2 years
• Adverse effects: Muscle/joint pain, alopecia, taste disturbances, weight loss, fatigue, nausea; >50% grade 3+ toxicity; ~50% discontinue by 1 year
• A 2026 meta-analysis confirmed safety and efficacy of both agents in head/neck BCC (PMID: 41025405)

• Cemiplimab (PD-1 inhibitor): 31% objective response rate in phase II trial; 85% of responses ongoing at 12 months; significant grade 3+ adverse events (~50%)
• Fischer's Mastery of Surgery 8e, pp. 1892-1894

Prognosis & Follow-Up

• Local recurrence rate after appropriate treatment is low (1-5%), but ~40% of patients will develop a new BCC within 5 years
• Metastasis is rare (<0.1%) but can occur with neglected, deeply invasive tumors
• Locally neglected tumors can invade bone, orbit, or facial sinuses ("rodent ulcer")
• Lifelong annual skin surveillance is recommended

Key Differentials

Basal Cell Carcinoma (BCC) — Summary

• Nodular - pearly papule, rolled edges, telangiectasias, central ulceration (most common)
• Superficial - erythematous scaly plaque on trunk/limbs
• Morpheaform/Infiltrative - scar-like, ill-defined borders; highest risk

• Mohs surgery - gold standard for high-risk/facial BCC (~1-4% recurrence)
• Surgical excision - standard for low-risk BCC
• Topical (imiquimod, 5-FU), cryotherapy, PDT - low-risk only
• Vismodegib / Sonidegib (SMO inhibitors) - locally advanced or metastatic BCC
• Cemiplimab (PD-1 blocker) - second-line after Hh inhibitor failure

Basal Cell Carcinoma (BCC) — 5 Marks MBBS Answer

Definition

Etiology & Risk Factors

• Chronic UV/sun exposure (most important)
• Fair skin, elderly, male
• Immunosuppression
• Gorlin syndrome (autosomal dominant; germline PTCH1 mutation)
• Ionizing radiation, arsenic exposure

Pathogenesis

Clinical Features

• Occurs on sun-exposed areas (face, especially nose, eyelids, cheeks)
• Classic lesion: Pearly/translucent papule with:
  • Rolled/raised edges
  • Central ulceration → "Rodent ulcer"
  • Surface telangiectasias

Types (High-yield)

Histology

• Nests of basaloid cells with hyperchromatic nuclei
• Peripheral nuclear palisading
• Stromal clefting (retraction artifact between tumor nests and stroma)
• No keratin pearls (differentiates from SCC)

Treatment

1. Mohs micrographic surgery — gold standard (high-risk/facial)
2. Surgical excision — 4 mm margins for nodular type
3. Radiotherapy — for inoperable cases
4. Topical imiquimod / 5-FU — superficial BCC
5. Vismodegib (Hh inhibitor) — locally advanced / metastatic BCC

Prognosis

• Excellent with early treatment
• Metastasis rare (<0.1%)
• 40% develop a new BCC within 5 years — lifelong follow-up needed