Skin cancer - Melanoma, basal and squamous cell carcinoma

Common and specific risk factors

Basal cell carcinoma (BCC)

• Epidemiology and location: most common cancer in humans - 75-80 % of skin cancers; located in 85 % of cases on the face and neck (sun-exposed areas); nose (one-third of BCCs), cheeks, forehead, eyelids, peri-auricular region; occurs mainly between the ages of 50 and 80; very rarely metastatic (< 0.1 %) but locally destructive if neglected (ulceration of soft tissue and bone - «ulcus rodens»).
• Clinical forms: nodular BCC (most frequent form - 60 %): translucent pearly papule with rolled edges, telangiectatic vessels visible on surface, center may ulcerate (ulcero-nodular BCC); superficial BCC (20 %): slightly scaly erythematous plaque, fine pearly edges, trunk and limbs - often multifocal; sclerodermiform BCC (morpheiform - 10 %): ill-defined, pearly-white, indurated plaque, highly infiltrative, histological margins difficult to define - form at high risk of recurrence; pigmented BCC: pigmented variant of nodular - differential diagnosis with melanoma (presence of characteristic pearly margins).
• Diagnosis: clinical + dermoscopy (maple leaf structures, egg nests, tree-like telangiectasias, structured white-grey areas); confirmatory skin biopsy before treatment; MRI if there is any doubt about deep invasion (recurrent scleroderma forms).
• Treatment : surgical excision with safety margins (4-6 mm for low-risk forms, 3-5 mm for high-risk forms) - reference treatment with cure rate > 95 %; Mohs surgery (controlled micrography) - for high-risk forms (scleroderma, recurrent, high-risk location - nose, eyelids, lips, ears) - histological margins controlled intraoperatively, recurrence rate < 1 % ; topical treatment (vismodegib - hedgehog inhibitor - for advanced or metastatic unresectable BCCs); topical imiquimod and topical 5-FU for superficial BCCs; cryotherapy and curettage-electrocoagulation for small, low-risk superficial lesions.

Squamous cell carcinoma (SCC)

• Epidemiology and localization: 15-20 % of skin cancers; metastatic risk significantly higher than BCC (1-5 % on average, up to 30-40 % for high-risk forms - lip, ear, scar, immunocompromised); localized mainly on photo-exposed areas (lower lip, auricle, dorsum of hands, forearms, scalp of bald men) and on mucous membranes (lips, tongue, genitals - often associated with HPV).
• Forms and clinical presentation : keratotic, crusty, indurated, irregular-edged skin lesion, which may ulcerate - often against a background of sun-damaged skin (dermatoheliosis) or advanced actinic keratosis ; may take on the appearance of an indurated plaque, a chronic non-healing ulcer, or a budding lesion bleeding easily on contact; in situ form (Bowen's disease) - well-defined erythematous scaly plaque without invasion of the dermis - risk of invasive transformation 3-5 % per year
• High-risk criteria (unfavorable prognostic factors): thickness > 2 mm (adapted Breslow) or Clark level IV-V; peri-neuronal or vascular invasion; ear, lip, genitalia, scar localization; poorly differentiated histological grade (grade 3-4); size > 2 cm; immunodepression; recurrence.
• Treatment : surgical excision with safety margins (4-10 mm depending on risk) - reference treatment; Mohs surgery for high-risk forms in functional or aesthetic areas; sentinel node biopsy if high-risk factors; curettage-electrocoagulation for low-risk in situ forms; cryotherapy for multiple actinic keratoses (primary prevention); imiquimod, topical 5-FU or diclofenac 3 gel % for actinic keratoses; systemic chemotherapy (cisplatin ± 5-FU) or cetuxumab (anti-EGFR) for metastatic or unresectable forms; cemiplimab (anti-PD-1, Libtayo) - approved for advanced cutaneous SCC (2018) - objective response rate 47 %

Malignant melanoma

• Clinical forms : melanoma with superficial extension (SSM - 70 %) - flat polychromatic lesion with radial growth at first, then late vertical invasion; nodular melanoma (NM - 15 %) - vertical growth from the start, poorer prognosis because often thick at diagnosis ; Dubreuilh melanoma (lentigo maligna melanoma - 10 %) - elderly subject, face, slow horizontal growth on pre-existing lentigo maligna; acral lentiginous melanoma (ALM - 2-5 %) - palms, soles, under the nails (subungual) - more frequent in dark-skinned subjects, where it is the most common melanoma.
• ABCDE rule for early detection: A = Asymmetry (one half different from the other); B = Irregular, ill-defined, notched or polycyclic edges; C = Multiple colors in the same lesion (beige, brown, black, red, white, blue) - chromatic heterogeneity; D = Diameter > 6 mm (size of a pencil eraser) - caution: melanomas can be small; E = Evolution - any skin lesion that changes size, shape, color, bleeds or itches should be shown to a doctor; criterion E is the most sensitive and the most important - an evolving lesion justifies a consultation even if the other criteria are not present
• Ugly duckling sign: any lesion that stands out from a patient's other nevi - larger, darker, more irregular - merits evaluation independently of ABCDE criteria; some nodular melanomas are symmetrical and monochrome (amelanotic melanoma - pink or flesh) and escape the ABCDE rule.
• TNM staging (AJCC 8th edition 2017): T = Breslow thickness (mm) and ulceration; N = nodes; M = distant metastases; stage T1a ( 97 % at 5 years; stage IV (M1c - visceral metastases) - median survival 6-9 months without treatment, 12-24 months with immunotherapy, 36-48 months with anti-BRAF/MEK (BRAF-mutated) targeted therapies.
• Molecular alterations and biomarkers : BRAF V600E mutation - present in 40-50 % of cutaneous melanomas (50 % V600E, 10-15 % V600K, 5-6 % V600R) - therapeutic target of BRAF/MEK inhibitors; NRAS mutation (15-25 %) - no approved targeted therapy but slightly better prognosis with immunotherapy; KIT mutation (5-10 % - acral and mucosal melanomas) - imatinib possible; CCND1 amplification; uveal melanomas (eye) - GNAQ/GNA11 mutations, highly resistant to treatment

Melanoma treatment by stage

Prevention and photoprotection

• Daily sun protection: use a broad-spectrum sunscreen (UVA + UVB) with a protection factor of SPF ≥ 30 (ideally SPF 50+) - apply 15 to 30 minutes before exposure, repeat every 2 hours and after each swim or significant perspiration; apply generously (2 mg/cm² of skin - i.e. approximately 35 mL for the entire body of an adult) - most users apply only 25 to 50 % of the required amount, reducing actual effectiveness
• Avoid intense sun exposure during peak hours (10:00 am to 4:00 pm from May to September in Quebec); seek shade; cover-up clothing, wide-brimmed hat (UV protection ≥ 7.5 cm), sunglasses with certified UV filter
• Avoid tanning booths at all costs - in Quebec, they're banned for under-18s; artificial tanning is not a «healthy» tan - it's the result of a DNA defense response to UV damage, and doesn't effectively protect against subsequent sunburns
• Monthly skin self-examination: examine the entire skin surface (with a mirror and the help of a relative for the back and scalp) - note any new or changing lesions according to the ABCDE rule; annual dermatological consultation recommended for high-risk individuals (phototype I-II, numerous nevi, personal or family history of melanoma).
• Protecting children: children's skin is particularly vulnerable - sunburn in childhood and adolescence is the most strongly associated risk factor for melanoma; SPF 50+ for children, avoid direct exposure before 6 months, systematic shade and protective clothing

Consult at Clinique Omicron

Clinique Omicron physicians perform a complete skin examination, use dermoscopy to assess suspicious pigmented lesions, prescribe skin biopsies and refer confirmed skin cancers to partner dermatologists and oncologists for surgical and systemic management. Consultations are available at our points of service in Quebec, as well as via telemedicine. To book an appointment, visit cliniqueomicron.ca.

The contents of this page are provided for information purposes only and do not replace the advice of a qualified healthcare professional. Any suspected skin lesion should be evaluated by a physician - biopsy is the only method to confirm or exclude skin cancer.