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Monday, August 11, 2025

Non-melanoma skin cancer


Introduction
Non-melanoma skin cancer (NMSC) is the most common group of skin malignancies, encompassing primarily basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), as well as less common variants such as Merkel cell carcinoma, adnexal carcinomas, and cutaneous lymphomas. These cancers arise from keratinocytes and other epidermal or adnexal structures and, unlike melanoma, typically have a much lower metastatic potential. However, untreated NMSC can cause significant local tissue destruction, functional impairment, and disfigurement.

Epidemiology

  • NMSC accounts for over 90% of all skin cancers.

  • Basal cell carcinoma is the most common subtype, representing ~75–80% of cases; SCC accounts for ~20–25%.

  • More prevalent in fair-skinned individuals and in populations with high cumulative ultraviolet (UV) exposure.

  • Incidence rates are increasing globally due to aging populations, increased outdoor activity, and improved detection.

Etiology and Risk Factors

Primary Risk Factor

  • Chronic UV radiation exposure (UVB wavelengths are most carcinogenic; UVA contributes to indirect DNA damage).

Additional Risk Factors

  • Fair skin, light eye and hair color.

  • History of sunburns, especially in childhood.

  • Immunosuppression (organ transplant recipients, HIV/AIDS).

  • Chronic skin inflammation or injury (burn scars, chronic ulcers).

  • Exposure to carcinogens (arsenic, polycyclic aromatic hydrocarbons).

  • Genetic syndromes (e.g., basal cell nevus syndrome, xeroderma pigmentosum).

  • Older age and male sex (due to occupational and lifestyle exposure).

Pathophysiology

  • UV radiation induces DNA damage, primarily cyclobutane pyrimidine dimers, leading to mutations in tumor suppressor genes (e.g., p53 in SCC) and signaling pathways (e.g., Hedgehog pathway mutations in BCC).

  • Immunosuppression reduces tumor surveillance, allowing malignant keratinocytes to proliferate.

Clinical Presentation

Basal Cell Carcinoma

  • Slowly growing, pearly or translucent papule/nodule with telangiectasia.

  • May ulcerate (“rodent ulcer”) and have rolled edges.

  • Often on sun-exposed areas: face, ears, neck.

Squamous Cell Carcinoma

  • Firm, red, scaly nodule or plaque.

  • May ulcerate or form a crust.

  • Often arises from actinic keratosis or Bowen’s disease.

  • Common on scalp, ears, hands, forearms.

Less common NMSC subtypes

  • Merkel cell carcinoma: rapidly growing, painless, firm, red-purple nodule.

  • Adnexal tumors: present as skin-colored or erythematous papules/nodules.

Diagnosis

Clinical assessment

  • Detailed history (onset, growth, sun exposure, immunosuppression, prior skin cancers).

  • Full skin examination for other suspicious lesions.

Biopsy (mandatory for diagnosis)

  • Punch, shave, or excisional biopsy depending on lesion size and site.

  • Histopathology confirms tumor type, depth, and degree of differentiation.

Additional investigations (in high-risk or advanced cases)

  • Imaging (CT, MRI, ultrasound) for large, invasive, or metastatic lesions.

  • Sentinel lymph node biopsy for select high-risk SCC or Merkel cell carcinoma.

Treatment

Treatment choice depends on cancer type, size, location, depth, and patient comorbidities.

1. Surgical Approaches

  • Standard surgical excision: Removal with predetermined margins (typically 4 mm for low-risk BCC, 4–6 mm for SCC).

  • Mohs micrographic surgery: Layer-by-layer excision with immediate histologic examination; gold standard for high-risk, recurrent, or cosmetically sensitive area lesions (face, periorbital, perinasal, perioral regions).

2. Destructive Techniques (for superficial or low-risk lesions)

  • Curettage and electrodessication.

  • Cryotherapy (liquid nitrogen application).

3. Topical Treatments (mainly for superficial BCC or SCC in situ)

  • Imiquimod 5% cream: Apply once daily, 5 times per week for 6–12 weeks.

  • 5-Fluorouracil (5-FU) 5% cream: Apply once or twice daily for 2–6 weeks depending on protocol.

4. Photodynamic Therapy (PDT)

  • Topical photosensitizer (e.g., methyl aminolevulinate) followed by light activation to destroy tumor cells; used for superficial BCC and actinic keratoses.

5. Radiotherapy

  • Option for patients unfit for surgery or for tumors in anatomically challenging sites.

6. Systemic and Targeted Therapy (for advanced/metastatic disease)

  • Vismodegib (oral Hedgehog pathway inhibitor) 150 mg once daily for advanced BCC.

  • Sonidegib 200 mg once daily for locally advanced BCC.

  • Cemiplimab (PD-1 inhibitor) 350 mg IV every 3 weeks for advanced SCC.

  • Pembrolizumab (PD-1 inhibitor) 200 mg IV every 3 weeks for metastatic SCC.

Follow-Up and Surveillance

  • Regular dermatologic follow-up (every 6–12 months, or more frequent for high-risk cases).

  • Education on skin self-examination.

  • Sun protection counseling (broad-spectrum sunscreen SPF ≥30, protective clothing, avoidance of peak UV hours).

Prognosis

  • BCC: Excellent prognosis; metastasis is extremely rare.

  • SCC: Slightly higher metastatic potential (~2–5% overall); early treatment ensures high cure rates.

  • Risk of recurrence is higher for incompletely excised, high-risk, or immunosuppressed patients.

  • Patients with one NMSC have a significantly increased risk of developing another within 5 years.





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