12.4 Nodules, Tumors & Cutaneous Oncology

Cutaneous malignancies and severe cutaneous adverse reactions (SCAR) represent critical clinical scenarios where rapid recognition, precise histologic staging, and multidisciplinary emergency interventions dictate patient survival.

1. Cutaneous Oncology

Cutaneous Melanoma

• Epidemiology & Major Risk Factors: Fair skin phototype (Fitzpatrick I-II: easily burns, rarely tans), red/blond hair, blue eyes, intermittent intense UV radiation (blistering childhood sunburns), indoor tanning bed use, elevated total nevus count (>50-100 typical nevi), presence of multiple dysplastic (atypical) nevi, family or personal history of melanoma, germline mutations in CDKN2A (p16/INK4a) or CDK4, and chronic immunosuppression.
• Clinical ABCDE Diagnostic Framework:
  • A — Asymmetry: One half of the lesion does not mirror the other half along either axis.
  • B — Border Irregularity: Edges are notched, scalloped, ragged, jagged, or poorly defined.
  • C — Color Variation: Non-uniform pigmentation with variegated shades of brown, black, tan, blue/gray, red, or white (hypopigmented areas indicating spontaneous regression).
  • D — Diameter: Classically >= 6 mm (approximate diameter of a pencil eraser); however, many early melanomas are detected at <6 mm.
  • E — Evolving: Any change in size, shape, surface contour, color, or the onset of new symptoms (pruritus, tenderness, bleeding, crusting) over time. This is the single most sensitive clinical indicator of malignancy.
  • "Ugly Duckling" Sign: A melanocytic lesion that looks morphologically disparate (outlier in color, size, or shape) from all other background nevi in a given patient.
• Definitive Biopsy Technique (Critical Board Rule):
  • Complete Full-Thickness Excisional Biopsy with narrow 1 to 3 mm normal margins extending into the subcutaneous fat (via elliptical excision, punch excision, or deep saucerization/scoop shave that encompasses the entire base of the lesion).
  • Strictly Contraindicated: Superficial shave biopsy, cryosurgery, laser ablation, or electrocautery. Transecting the base of a primary melanoma destroys the ability to measure Breslow depth, compromising TNM staging, prognostic stratification, and surgical margin determination.
• Microscopic Prognostic Factors & Staging:
  • Breslow Tumor Thickness: The single most powerful prognostic indicator for primary localized melanoma. Measured in millimeters from the top of the epidermal granular layer (or base of ulcer) to the deepest invasive malignant melanocyte in the dermis/subcutis.
  • Ulceration: Presence of histologic ulceration upstages the T-category (e.g., T1b vs T1a) and significantly worsens prognosis.
  • Mitotic Rate: Number of mitoses per mm2; elevated mitotic rate indicates aggressive biology.
  • Sentinel Lymph Node Biopsy (SLNB): Recommended for clinical Stage I/II melanoma with: (1) Breslow thickness >= 0.8 mm (T1b-T4); OR (2) Breslow thickness < 0.8 mm WITH histologic ulceration (T1b). (SLNB is not recommended for T1a [<0.8 mm non-ulcerated] due to <5% nodal positivity).
• Definitive Wide Local Surgical Margins:

• Targeted Therapy & Checkpoint Immunotherapy:
  • BRAF V600E / V600K Mutation: Present in ~50% of cutaneous melanomas. Mandates reflex molecular testing in Stage III/IV disease.
  • Combined BRAF + MEK Inhibitors: Produces rapid objective response rates (>65-75%): Dabrafenib + Trametinib, Encorafenib + Binimetinib, or Vemurafenib + Cobimetinib.
  • Immune Checkpoint Inhibitors (First-Line Standard for Advanced/Metastatic Disease):
    • Anti-PD-1 Monoclonal Antibodies: Pembrolizumab or Nivolumab (monotherapy in adjuvant Stage IIB/IIC/III or first-line metastatic).
    • Combination Dual Checkpoint Blockade: Nivolumab + Ipilimumab (anti-CTLA-4) provides highest median overall survival (CheckMate 067 trial) but carries high rates (~55%) of severe Grade 3-4 immune-related adverse events (irAEs: colitis, hypophysitis, hepatitis, thyroiditis, pneumonitis).
    • Novel Combinations: Nivolumab + Relatlimab (anti-LAG-3) (Opdualag; superior progression-free survival compared to nivolumab monotherapy with lower toxicity than ipilimumab/nivolumab).

Non-Melanoma Skin Cancers (NMSC)

Basal Cell Carcinoma (BCC)

• Epidemiology: The most common human malignancy worldwide (>80% of all skin cancers). Arises from non-keratinizing basal cells of the interfollicular epidermis and hair follicles. Characterized by slow local invasion and tissue destruction ("rodent ulcer"); metastasis is extraordinarily rare (<0.1%).
• Clinical Subtypes & Features:
  • Nodular BCC (~60-70%): Classic pearly pink or translucent dome-shaped papule/nodule with rolled borders, central depression/ulceration, and fine, branching arborizing telangiectasias.
  • Superficial BCC (~15-20%): Erythematous, thin scaly plaque with a fine, thread-like pearly rolled border, common on trunk and extremities.
  • Morpheaform / Infiltrative BCC: Indurated, sclerotic, scar-like white/yellow plaque with poorly defined clinical margins; highly aggressive with extensive subclinical microscopic extension.
• Management Modalities:
  • Standard Surgical Excision (4-5 mm margins): First-line for low-risk nodular/superficial lesions on trunk and extremities.
  • Electrodessication & Curettage (ED&C): Suitable only for small, low-risk superficial/nodular BCCs on non-facial sites.
  • Topical Therapy: Imiquimod 5% cream or 5-Fluorouracil (5-FU) 5% cream for superficial BCCs in non-critical areas.
  • Mohs Micrographic Surgery (MMS): Precise, tissue-sparing surgical technique involving immediate 100% intraoperative frozen-section peripheral and deep margin examination. Definitive indications for Mohs:
    1. High-Risk Anatomical Locations ("H-Zone" of Face): Nose, periorbital/eyelids, lips, ears, chin, temples, scalp, hands, feet, and genitalia.
    2. Aggressive Histological Subtypes: Morpheaform, infiltrative, micronodular, sclerosing, or perineural invasion.
    3. Recurrent or Incompletely Excised Tumors.
    4. Large Tumors: >2 cm on trunk/extremities, >1 cm on cheeks/forehead/neck, or >0.5 cm in high-risk zones.
  • Targeted Systemic Therapy for Locally Advanced / Metastatic BCC: Hedgehog Pathway Inhibitors (Vismodegib or Sonidegib) which bind to and inhibit the Smoothened (SMO) receptor, blocking downstream GLI1 oncogenic signaling. Adverse effects: severe muscle spasms, dysgeusia (taste loss), alopecia, and weight loss. Anti-PD-1 antibody Cemiplimab is second-line.

Squamous Cell Carcinoma (SCC) & Precursor Lesions

• Epidemiology: Second most common skin cancer (~20% of NMSC). Arises from malignant epidermal keratinocytes. Carries significant metastatic potential (overall ~2-5%, but >10-30% for high-risk lesions).
• Precursor Lesion — Actinic Keratosis (AK):
  • Rough, gritty, scaly erythematous macule or papule on chronically sun-damaged skin (face, balding scalp, ears, dorsal hands) with a characteristic "sandpaper-like" rough texture on palpation.
  • Pathology: Atypical keratinocytes confined to the lower epidermis (dysplasia). May progress to invasive cutaneous SCC (~0.1-1% per lesion per year; however, 60-80% of SCCs arise in actinic fields).
  • Treatment: Isolated lesions: Liquid nitrogen cryotherapy. Field cancerization (multiple lesions across sun-damaged field): Topical 5-Fluorouracil (5-FU) 5% cream BID for 2-4 weeks (inhibits thymidylate synthase; causes robust erythema/crusting), Topical Imiquimod 5% cream (TLR-7 agonist), Topical Tirbanibulin 1% ointment (5-day course), or Photodynamic Therapy (PDT).
• Clinical Presentation of Invasive SCC: Indurated, firm, hyperkeratotic, erythematous nodule or plaque with thick adherent scale, central crusting, ulceration, or cutaneous horn.
• High-Risk Features for SCC Recurrence & Metastasis:
  • Anatomical site: Vermilion border of the lower lip, external ear/pinna, temple, and perineum/genitals.
  • Host factors: Solid organ transplant recipients (SOTRs) on chronic immunosuppression (65 to 100-fold higher incidence of SCC than general population; highly aggressive). Consider switching calcineurin inhibitors (tacrolimus) to mTOR inhibitors (Sirolimus). Chronic non-healing scars / burn wounds (Marjolin's Ulcer; carries >30% metastatic rate).
  • Tumor depth & histology: Thickness >4 mm, Clark level IV/V, perineural invasion (>=0.1 mm), poorly differentiated.
• Management: Low-risk: Surgical excision (4-6 mm margins) or ED&C. High-risk / facial / transplant patients: Mohs Micrographic Surgery. Advanced / Metastatic SCC: Anti-PD-1 immunotherapy (Cemiplimab or Pembrolizumab; achieves ~50% objective response rate).

Keratoacanthoma & Cutaneous T-Cell Lymphoma (CTCL)

• Keratoacanthoma (KA): Rapidly enlarging, dome-shaped erythematous nodule with a distinctive central, smooth, crateriform keratin plug that evolves over weeks. Biologically and histologically treated as a variant of well-differentiated invasive Squamous Cell Carcinoma; standard management is complete surgical excision.
• Cutaneous T-Cell Lymphoma (Mycosis Fungoides & Sézary Syndrome):
  • Mycosis Fungoides (MF): Indolent clonal proliferation of skin-homing CD4+ memory T lymphocytes. Presents as chronic, pruritic, scaly erythematous patches and plaques in a "bathing-suit" distribution (buttocks, lower abdomen, inner thighs) that slowly progress to cutaneous tumors. Histopathology reveals epidermotropism of atypical lymphocytes with hyperconvoluted cerebriform nuclei forming intraepidermal clusters (Pautrier microabscesses). Early-stage therapy: Topical steroids, topical mechlorethamine (nitrogen mustard gel), phototherapy (NB-UVB / PUVA). Advanced-stage: Brentuximab vedotin (anti-CD30), Mogamulizumab (anti-CCR4), oral Bexarotene.
  • Sézary Syndrome: Aggressive leukemic variant of CTCL defined by the triad of: (1) Generalized pruritic erythroderma (>80% BSA); (2) Generalized lymphadenopathy; (3) Circulating malignant T cells with cerebriform nuclei (Sézary cells >= 1000/mcL or CD4/CD8 ratio >= 10).