17.4 Benign & Malignant Epidermal, Adnexal, Mesenchymal and Vascular Tumours, Cysts, Histiocytoses & Metastases
Key Takeaways
- Pilomatricoma is a benign calcifying tumour of hair matrix cells, usually on the head and neck of children, caused by CTNNB1 (beta-catenin) mutations, and multiple lesions suggest myotonic dystrophy.
- A sebaceous adenoma or carcinoma should prompt mismatch-repair protein immunohistochemistry and screening for Muir-Torre syndrome, a variant of Lynch syndrome.
- Extramammary Paget disease presents as a persistent red plaque of the vulva, scrotum, or perianal skin and needs a search for an underlying adenocarcinoma, especially with perianal disease.
- Langerhans cell histiocytosis in infants often causes a seborrhoeic-dermatitis-like eruption with purpura; the cells express CD1a and langerin (CD207), and many carry BRAF V600E.
- Breast cancer is the most common source of skin metastases in women and lung cancer in men, and an umbilical metastasis is called a Sister Mary Joseph nodule.
Last updated: September 2026
17.4 Benign & Malignant Epidermal, Adnexal, Mesenchymal and Vascular Tumours, Cysts, Histiocytoses & Metastases
This section completes the dermato-oncology syllabus. Cutaneous lymphomas, dermatofibrosarcoma protuberans, and Merkel cell carcinoma are covered in the lymphoma and rare neoplasm section, and Kaposi sarcoma in the herpesvirus and HIV sections.
Benign Epidermal Tumours
| Tumour | Key Features |
|---|---|
| Seborrhoeic keratosis | "Stuck-on" warty papules in older adults; dermoscopy shows milia-like cysts and comedo-like openings (see the dermoscopy section). Dermatosis papulosa nigra is the facial variant in darker skin. A sudden eruption may be the sign of Leser-Trélat |
| Clear cell acanthoma | Moist red papule on the leg; dermoscopy shows dotted vessels in a "string of pearls" pattern |
| Epidermal naevus | Linear warty plaques along Blaschko lines from birth; widespread lesions can be part of epidermal naevus syndromes |
| Naevus sebaceus | Yellow-orange hairless plaque on the scalp or face at birth, becoming warty at puberty. Secondary tumours are mostly benign (trichoblastoma, syringocystadenoma papilliferum); basal cell carcinoma is rare. Excision is optional |
| Acrochordon (skin tag) | Soft pedunculated papules in flexures; linked to obesity and insulin resistance |
Cysts
| Cyst | Features |
|---|---|
| Epidermoid (infundibular) cyst | Firm nodule with a central punctum, containing keratin; ruptured cysts become inflamed. Multiple cysts in unusual sites suggest Gardner syndrome |
| Pilar (trichilemmal) cyst | Smooth, firm scalp cysts, often multiple and familial; no punctum |
| Steatocystoma multiplex | Many small yellow cysts on the chest and axillae with oily content; KRT17 mutations (pachyonychia congenita) |
| Dermoid cyst | Congenital cyst along embryonic fusion lines (lateral eyebrow). Midline nasal lesions need imaging before surgery because of possible intracranial extension |
| Milia | Tiny white keratin cysts; secondary milia follow blistering (porphyria cutanea tarda, epidermolysis bullosa) |
| Hidrocystoma | Translucent blue cysts around the eyelids |
Adnexal Tumours
| Tumour | Origin | Key Points |
|---|---|---|
| Syringoma | Eccrine duct | Small skin-coloured papules on the lower eyelids; eruptive syringomas and clear-cell variants in Down syndrome and diabetes |
| Trichoepithelioma | Hair follicle | Skin-coloured facial papules; multiple lesions with cylindromas and spiradenomas in Brooke-Spiegler syndrome (CYLD) |
| Cylindroma | Adnexal | Pink nodules on the scalp; multiple lesions can form a "turban tumour" (CYLD) |
| Pilomatricoma | Hair matrix | Hard, calcified, sometimes bluish nodule on the head, neck, or arms of children; the skin tents when stretched. CTNNB1 (beta-catenin) mutations. Multiple lesions suggest myotonic dystrophy, Gardner syndrome, or Turner syndrome. Histology shows shadow (ghost) cells |
| Trichilemmoma | Outer root sheath | Facial papules; multiple lesions in Cowden syndrome (PTEN) |
| Fibrofolliculoma | Hair follicle | Facial papules in Birt-Hogg-Dubé syndrome (FLCN) |
| Sebaceous hyperplasia | Sebaceous gland | Yellow umbilicated papules with "crown" vessels on the face; very common and benign |
| Sebaceous adenoma / sebaceoma / sebaceous carcinoma | Sebaceous gland | Should prompt mismatch-repair (MMR) protein immunohistochemistry and screening for Muir-Torre syndrome (Lynch syndrome variant) |
Malignant Adnexal Tumours and Extramammary Paget Disease
- Sebaceous carcinoma: most often on the eyelid (meibomian glands). It mimics chalazion or blepharitis, so a persistent "chalazion" needs biopsy. It can metastasise and is linked to Muir-Torre syndrome.
- Microcystic adnexal carcinoma: a slow-growing, indurated plaque on the upper lip or face with deep infiltration and perineural spread. Micrographic surgery is preferred.
- Porocarcinoma: malignant eccrine tumour on the legs or head of older adults.
- Extramammary Paget disease (EMPD): a persistent, itchy, red, moist or scaly plaque of the vulva, scrotum, perianal, or axillary skin, often mistaken for eczema or candidiasis. Histology shows large pale Paget cells in the epidermis (CK7 positive). Primary EMPD is intraepidermal adenocarcinoma. Secondary EMPD reflects an underlying colorectal, anal, bladder, or cervical cancer; perianal disease and CK20 positivity raise suspicion. Always search for an underlying adenocarcinoma. Treatment includes excision (often micrographic), imiquimod, photodynamic therapy, or radiotherapy, with high recurrence rates.
Benign Mesenchymal Tumours
| Tumour | Features |
|---|---|
| Dermatofibroma | Firm papule on the legs with a positive dimple sign when pinched; dermoscopy shows a central white patch with a peripheral delicate network |
| Lipoma | Soft, mobile subcutaneous mass. Angiolipomas are tender and multiple. Large, deep, or fast-growing lesions need imaging to exclude liposarcoma |
| Neurofibroma | Soft skin-coloured papule that "buttonholes" on pressure; multiple lesions suggest NF1 |
| Schwannoma | Tender nodule along a nerve; multiple lesions in NF2-related schwannomatosis |
| Leiomyoma | Painful, cold-sensitive red-brown papules. Multiple lesions suggest hereditary leiomyomatosis and renal cell cancer (FH) |
| Keloid and hypertrophic scar | See the surgical complications section |
Acquired Vascular Tumours and Lesions
| Lesion | Features |
|---|---|
| Cherry angioma | Bright red papules on the trunk, increasing with age |
| Pyogenic granuloma (lobular capillary haemangioma) | Rapidly growing, friable, bleeding red papule on fingers, lips, or gums, often after minor trauma or in pregnancy; also with retinoids and EGFR inhibitors. Curettage with cautery or excision, with histology (amelanotic melanoma can mimic it) |
| Angiokeratoma | Dark red-purple warty papules. Many small lesions in a "bathing trunk" distribution suggest Fabry disease (GLA, alpha-galactosidase A deficiency) |
| Venous lake | Soft blue papule on the lips or ears of older adults; empties on pressure |
| Angiosarcoma | Bruise-like purple patches and nodules on the scalp and face of elderly men, in chronic lymphoedema (Stewart-Treves syndrome), or after radiotherapy. Poor prognosis; wide surgery, radiotherapy, and taxanes |
| Atypical fibroxanthoma / pleomorphic dermal sarcoma | Rapidly growing ulcerated nodule on sun-damaged scalp of older men; diagnosis of exclusion using immunohistochemistry; complete excision |
Histiocytoses
| Disorder | Features |
|---|---|
| Langerhans cell histiocytosis (LCH) | Usually children. In infants: seborrhoeic-dermatitis-like scalp and flexural eruption with petechiae or purpura, erosions, and sometimes lytic bone lesions, diabetes insipidus, and marrow or liver involvement. Cells are CD1a and langerin (CD207) positive and often carry BRAF V600E. The self-healing congenital form (Hashimoto-Pritzker) still needs systemic evaluation |
| Juvenile xanthogranuloma | Yellow-orange papules in infants and young children, usually resolving. Eye involvement can cause hyphaema and glaucoma. Associated with NF1, and the combination of JXG and NF1 is linked to juvenile myelomonocytic leukaemia |
| Rosai-Dorfman disease | Massive painless lymphadenopathy, skin nodules; emperipolesis on histology |
| Reticulohistiocytoma and multicentric reticulohistiocytosis | Papules and destructive arthritis; the multicentric form may be paraneoplastic |
| Xanthoma disseminatum and necrobiotic xanthogranuloma | See the deposition disorders section |
Cutaneous Metastases
- Skin metastases occur in a small proportion of patients with internal cancer and usually mean advanced disease.
- Most common primary sites: breast cancer in women, and lung cancer (then colorectal and melanoma) in men.
- Patterns: firm skin-coloured, red, or violaceous nodules; carcinoma erysipeloides (an inflammatory red plaque from lymphatic spread, often breast); carcinoma en cuirasse (sclerotic plaques on the chest wall); scalp nodules and alopecia neoplastica; and a Sister Mary Joseph nodule at the umbilicus (gastric, colorectal, ovarian, or pancreatic cancer).
- Diagnosis: biopsy with immunohistochemistry to identify the primary (for example CK7/CK20, TTF-1 for lung, GATA3 for breast, CDX2 for colorectal).
Test Your Knowledge
An 8-year-old boy has a hard, 1.5 cm skin-coloured-to-bluish nodule on his neck that has been present for a year. When the skin is stretched, it tents over angular facets. Histology shows basaloid cells and shadow (ghost) cells with calcification. Which statement is correct?
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Test Your Knowledge
A 68-year-old man has had a persistent red, moist plaque around the anus for 2 years that did not respond to antifungals or topical steroids. Biopsy shows large pale intraepidermal cells that are CK7 and CK20 positive. What is the most important next step?
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Test Your Knowledge
A 9-month-old infant has a persistent scaly, crusted eruption of the scalp and groin that looks like seborrhoeic dermatitis, with scattered petechiae and purpura, and a lytic skull lesion. Which immunohistochemical profile confirms the likely diagnosis?
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Test Your Knowledge
Which primary cancer is the most common source of cutaneous metastases in women?
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D