Basal Cell Carcinoma

Introduction & Risk Factors - The Sun's Kiss

• Most common human malignancy; locally invasive, slow-growing tumor.
• Origin: Basal layer of epidermis or hair follicles. Low metastatic potential.
• Primary Risk Factors:
  • UV Radiation: Chronic sun exposure (UVB > UVA), history of sunburns.
  • Phenotype: Fair skin (Fitzpatrick I-II), light hair/eyes.
  • Age: Typically > 40 years.
  • Genetics: Gorlin syndrome (NBCCS), Xeroderma Pigmentosum (XP).
  • Immunosuppression (e.g., organ transplant recipients).
  • Others: Ionizing radiation, arsenic, prior BCC.

⭐ BCC constitutes approximately 80% of all non-melanoma skin cancers (NMSC).

Pathogenesis (Hedgehog) - Hedgehog's Hijack

• Core: Uncontrolled Hedgehog (Hh) pathway.
• "Hedgehog's Hijack":
  • Normal: SHH ligand binds PTCH1 (receptor); PTCH1's inhibition of SMO (transducer) is lifted → GLI activation → controlled growth.
  • BCC (UV-induced mutations):
    • PTCH1 (tumor suppressor) Loss-of-Function (LoF, ~90%): Fails to inhibit SMO.
    • SMO (oncogene) Gain-of-Function (GoF, ~10%): Constitutively active.
  • Outcome: Constitutive SMO activation → ↑GLI activity → uncontrolled proliferation.
• Gorlin Syndrome: Germline PTCH1 mutation.

⭐ UV-induced PTCH1 mutations are key in most sporadic BCCs.

Clinical Types & Sites - The Many Masks

• Nodular (~60%): Most common. Pearly papule/nodule, telangiectasias, rolled border. Central ulcer (rodent ulcer). Site: Head/neck (esp. nose).
• Superficial (~30%): Erythematous, scaly plaque; thread-like border. Site: Trunk, shoulders.
• Morpheaform/Sclerosing (~5-10%): Waxy, scar-like plaque; ill-defined. Aggressive, ↑recurrence. Site: Mid-face.
• Pigmented: Brown/black pigment in any type. Mimics melanoma.
• Fibroepithelioma of Pinkus (FEP): Rare. Firm, pink papule. Site: Lumbosacral.
• Sites: >80% head & neck (sun-exposed). Nose most common.

  ⭐ Nodular BCC: most common type; pearly papule with telangiectasias, often on nose. oka

Diagnosis & Histology - Clues in Cells

• Dermoscopy (ELM): Key diagnostic aid.
  • Arborizing (branching) telangiectasias.
  • Blue-gray globules/ovoid nests.
  • Spoke-wheel areas, leaf-like structures.
  • Shiny white structures (chrysalis).
  • Ulceration.
• Skin Biopsy: Essential for confirmation (shave, punch, excisional).
• Histopathology (H&E stain): 📌 BCC = Blue Cells, Clefts, Palisading.
  • Tumor islands of basaloid cells (blue): scant cytoplasm, hyperchromatic nuclei.
  • Peripheral palisading: columnar cells at nest periphery align.
  • Stromal retraction (clefts): artifactual spaces around tumor islands.
  • Mucinous stroma.

  ⭐ Peripheral palisading of nuclei and peritumoral stromal retraction are pathognomonic histological hallmarks of BCC.

Treatment & Prognosis - Erase & Chase

• Surgical (Gold Standard):
  • Excision: 3-5 mm margins (low-risk).
  • Mohs Micrographic Surgery (MMS): Highest cure, tissue sparing. For H-zone, recurrent, large, aggressive.
  • Curettage & Electrodessication (C&E): Small, superficial, low-risk.
• Non-Surgical:
  • Topical: Imiquimod, 5-FU (superficial BCC).
  • Radiotherapy (RT): Adjuvant/primary if surgery contraindicated.
  • Systemic: Vismodegib, Sonidegib for advanced/metastatic.
• Prognosis: Excellent (>95% 5-yr cure). Recurrence ↑ with aggressive subtypes, perineural invasion.

⭐ Mohs Micrographic Surgery offers the highest cure rates (up to 99%) and best tissue conservation, vital for facial BCCs.

High‑Yield Points - ⚡ Biggest Takeaways

• Most common human malignancy, linked to chronic sun (UVB) exposure.
• Slow, local invasion is characteristic; metastasis is extremely rare.
• Classic: pearly papule/nodule with telangiectasias, rolled borders, and central ulceration (rodent ulcer).
• Histo: nests of basaloid cells, peripheral palisading, and stromal retraction.
• Affects sun-exposed areas (face, neck); nose is a very common site.
• Nodular BCC is the most frequent subtype.
• Multiple early BCCs suggest Gorlin syndrome.