Skin and Soft Tissue Tumours
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Direct answer
Basal cell carcinoma, the most common skin cancer, is a pearly nodule with rolled edges and telangiectasia on sun-exposed skin of older adults; its nests of basaloid cells show peripheral palisading, it erodes locally as the rodent ulcer, and it essentially never metastasises. Squamous cell carcinoma arises in actinic keratoses and forms keratin pearls, can metastasise, and in Indian practice is dominated by oral disease from smokeless tobacco. Malignant melanoma prognosis tracks the Breslow thickness in millimetres, and in Indian patients the dominant subtype is acral lentiginous melanoma of the sole, not the sun-driven superficial spreading type of fair skin. Rhabdomyosarcoma is the commonest soft tissue sarcoma of children; liposarcoma and undifferentiated pleomorphic sarcoma lead in adults.
What you must remember
- Basal cell carcinoma: basaloid nests with peripheral palisading and artifactual clefting; PTCH1-hedgehog pathway (Gorlin syndrome gives multiple tumours with palmar pits); locally invasive, metastasis vanishingly rare; excision or Mohs surgery.
- Squamous cell carcinoma: precursor actinic keratosis; keratin pearls and intercellular bridges; immunosuppression (transplant recipients) and chronic scars — Marjolin ulcer denotes carcinoma arising in a chronically unstable scar or fistula; Indian burden: oral squamous carcinoma with gutkha and areca nut, and oral submucous fibrosis as the predisposed field.
- Melanoma subtypes: superficial spreading is the commonest in white skin; nodular grows vertically from the start and presents thick; lentigo maligna on chronically sun-damaged elderly skin; acral lentiginous — palms, soles, subungual — is the dominant subtype in dark-skinned and Indian patients, independent of ultraviolet exposure.
- Melanoma rules: ABCDE of asymmetry, border, colour, diameter, evolution; Breslow thickness (vertical measurement in millimetres) is the strongest prognostic factor; radial growth spreads within the epidermis, vertical growth invades and metastasises.
- Mycosis fungoides: cutaneous T-cell lymphoma with patches then plaques then tumours; Pautrier microabscesses (intraepidermal clusters of atypical lymphocytes); leukaemic spread is Sezary syndrome.
- Benign-to-malignant soft tissue pairs: lipoma is the commonest benign adult soft tissue tumour, liposarcoma the commonest adult sarcoma — myxoid type carrying its own t(12;16); Kaposi sarcoma (HHV-8) in AIDS presents as violaceous cutaneous plaques.
- Rhabdomyosarcoma: the commonest paediatric soft tissue sarcoma — embryonal (children, genitourinary botryoid grape-like variant), alveolar (adolescents, worst prognosis, PAX3-FOXO1 fusion), pleomorphic (adults).
- Synovial sarcoma: young adults, around the knee despite the name, biphasic epithelial and spindle components, t(X;18) translocation.
A pigmented lesion on the sole
A 55-year-old agricultural worker presents with a nine-month history of an irregular dark lesion on the sole of the right foot, recently ulcerating and surrounded by satellite pigment. This is the Indian melanoma presentation, and the reasoning is geographical as much as dermatological: acral lentiginous melanoma arises on non-sun-exposed sites, so the usual ultraviolet-narrative misleads, and diagnosis is delayed precisely because the sole is not examined and a pigmented lesion there is attributed to a callus or wart. The biopsy shows atypical melanocytes tracking along the basal layer before invading the dermis — the radial-to-vertical progression that Breslow quantified: the vertical height from the granular layer to the deepest tumour cell, measured in millimetres, because survival curves fall stepwise across its thresholds (under 1 millimetre excellent, over 4 millimetres grim).
Management follows thickness — wide local excision margins widen with Breslow depth, and sentinel node biopsy is offered once thickness crosses about one millimetre. The contrast case on the same ward is the elderly man with a pearly rolled nodule below the eye: basal cell carcinoma, treated by excision with clear margins or Mohs micrographic surgery in the cosmetically critical central face, and cured.
Where students slip
Melanoma is treated as a disease of sun exposure full stop, and the acral lentiginous subtype of Indian patients is forgotten — an examinee who mentions it unprompted demonstrates real preparation. Breslow thickness is confused with Clark level (anatomical depth of invasion by skin layer), and modern practice retains Breslow as the prognostic variable. Second, the sarcoma subtypes get shuffled: alveolar rhabdomyosarcoma, not embryonal, carries the worst paediatric prognosis and the PAX fusion; and "synovial" sarcoma has nothing to do with joints — a young adult's peri-patellar mass with the t(X;18) is the exam vignette.
Frequently asked questions
Which is the most common skin cancer and what is its behaviour?
Basal cell carcinoma — pearly, rolled-edge nodule with peripheral palisading; locally destructive (rodent ulcer) but virtually non-metastasising.
Which melanoma subtype predominates in Indian patients?
Acral lentiginous melanoma of palms, soles and nail beds, unrelated to ultraviolet exposure and often diagnosed late.
What does the Breslow thickness measure?
The vertical depth of melanoma invasion from the granular layer in millimetres — the strongest single prognostic factor, guiding excision margins and sentinel node decisions.
What are Pautrier microabscesses?
Intraepidermal nests of atypical CD4-positive T lymphocytes in mycosis fungoides, the cutaneous T-cell lymphoma.
Which is the commonest soft tissue sarcoma of children?
Rhabdomyosarcoma — embryonal including botryoid variants in younger children, alveolar with the worst prognosis and PAX3-FOXO1 fusion in adolescents.
Which translocation defines synovial sarcoma?
t(X;18), producing the SS18-SSX fusion; despite the name it arises near, not in, joints of young adults.