Specialty Guide · Path-iQ Global Pathology Review
Dermatopathology is the subspecialty concerned with the diagnosis of skin diseases by microscopic examination of skin biopsies. It sits at the interface of dermatology and pathology, and its practitioners are often trained in both. Melanoma staging, Mohs surgery support, and the classification of inflammatory skin diseases represent the three primary domains — each requiring mastery of distinct technical and interpretive skills.
Melanoma staging under the AJCC 8th edition (2017, in effect through 2026) integrates Breslow thickness, ulceration, mitotic rate, satellite nodules, and lymph node status. The pathology report for a primary melanoma excision must include all staging-relevant elements to enable accurate pT classification.
| pT Stage | Breslow Thickness | Ulceration / Mitoses | 5-Year Survival (approx.) |
|---|---|---|---|
| pTis | In situ (melanoma in situ) | N/A | >99% |
| pT1a | ≤0.8 mm | No ulceration; no mitoses | ~97% |
| pT1b | ≤0.8 mm with ulceration; OR 0.8–1.0 mm ± ulceration | Ulceration present OR thickness 0.8–1.0 mm | ~92% |
| pT2a | >1.0–2.0 mm | No ulceration | ~81% |
| pT2b | >1.0–2.0 mm | With ulceration | ~75% |
| pT3a | >2.0–4.0 mm | No ulceration | ~70% |
| pT3b | >2.0–4.0 mm | With ulceration | ~59% |
| pT4a | >4.0 mm | No ulceration | ~53% |
| pT4b | >4.0 mm | With ulceration | ~39% |
Key additional pathological features to report: Clark level (I–V); mitotic rate (mitoses/mm²); microsatellites or satellite nodules; lymphovascular invasion; neurotropism; regression; tumour subtype (superficial spreading, nodular, lentigo maligna, acral lentiginous, desmoplastic); and tumour-infiltrating lymphocytes (TILs: absent, non-brisk, brisk). Sentinel lymph node status (pN) and BRAF V600E/K mutation status are additional determinants of systemic therapy eligibility.
| Category | Tumour | Key Histological Features | Relevant Markers |
|---|---|---|---|
| Melanocytic — benign | Intradermal naevus | Nests of uniform melanocytes confined to dermis; maturation with depth; no pagetoid spread | S100+, Melan-A+, HMB-45 diminishes with depth |
| Melanocytic — benign | Dysplastic naevus | Architectural disorder (bridging, shoulders); cytological atypia; lamellar fibroplasia | S100+; FISH negative for melanoma copy changes |
| Melanocytic — malignant | Superficial spreading melanoma | Pagetoid spread; atypical junctional nests; poor maturation; Breslow measurement from granular layer | S100+, SOX10+, HMB-45+, Ki-67 elevated |
| Melanocytic — malignant | Desmoplastic melanoma | Spindle cells in dense fibrous stroma; perineural invasion; may lack pigment; S100+ but HMB-45− | S100+, SOX10+; HMB-45 often negative; BRAF usually wildtype |
| Keratinocytic — benign | Seborrhoeic keratosis | Acanthotic epidermis; basaloid cells; horn pseudocysts; sharp lateral borders | No malignant potential; CK5/6+ |
| Keratinocytic — premalignant | Actinic keratosis | Atypical keratinocytes in lower epidermis; sun-damaged dermis; parakeratosis alternating with orthokeratosis | p53 overexpression; Ki-67 elevated basally |
| Keratinocytic — malignant | Basal cell carcinoma (BCC) | Peripheral palisading; retraction artefact; mucin stroma; basaloid nests; subtypes: nodular, superficial, morphoeic | BerEP4+, BCL2+; p63+; EMA− |
| Keratinocytic — malignant | Squamous cell carcinoma (SCC) | Squamous differentiation, keratin pearls; invasive nests; sun-damaged dermis; degree of differentiation (well, moderate, poor) | CK5/6+, p40+, p63+; desmoplastic variant difficult |
| Adnexal — malignant | Merkel cell carcinoma | Dermal small blue round cell tumour; perivascular pattern; salt-and-pepper chromatin; crush artefact | CK20 dot+ (perinuclear); neurofilament+; Syn+; CgA+; TTF-1−; Merkel cell polyomavirus (MCPyV) T-antigen in 80% |
| Vascular | Angiosarcoma | Dissecting vascular channels between collagen; pleomorphic endothelial cells; post-radiation/lymphoedema context | CD31+, CD34+, ERG+; FLI1+; MYC amplification in post-radiation type |
Mohs micrographic surgery (MMS) is a specialised excision technique used primarily for BCC and SCC in cosmetically sensitive or recurrence-prone sites (nose, eyelid, ear, lip). Unlike standard excision with breadloaf sections, Mohs surgery examines 100% of the peripheral and deep margin by mapping tissue into precisely oriented horizontal sections — processed in the operating suite while the patient waits.
Mohs surgery achieves 5-year recurrence rates of <1% for primary BCC vs 5–10% for standard excision. Its tissue-sparing nature is particularly valued for periocular, perinasal, and labial tumours where reconstruction is complex.
| Reaction Pattern | Histological Features | Typical Diagnoses |
|---|---|---|
| Spongiotic | Intercellular oedema (spongiosis); lymphocyte exocytosis; parakeratosis | Eczema/atopic dermatitis, allergic contact dermatitis, nummular eczema, dyshidrosis |
| Psoriasiform | Regular epidermal acanthosis; suprapapillary thinning; Munro microabscesses; dilated papillary vessels | Psoriasis vulgaris, seborrhoeic dermatitis, chronic spongiotic dermatitis |
| Lichenoid (interface) | Band-like lymphocytic infiltrate hugging DEJ; vacuolar degeneration; colloid (Civatte) bodies; saw-tooth rete | Lichen planus, lichenoid drug reaction, lupus erythematosus, GVHD |
| Vesicular / bullous | Intraepidermal or subepidermal blister; location determines diagnosis (sub-basal = BP, intraepidermal = pemphigus) | Bullous pemphigoid (subepidermal + eosinophils), pemphigus vulgaris (suprabasal acantholysis), dermatitis herpetiformis (neutrophil tips) |
| Granulomatous | Histiocyte aggregates; epithelioid giant cells; necrosis (if caseating); foreign material | Sarcoidosis (naked granulomas), TB (caseating), granuloma annulare (interstitial), foreign body, leishmaniasis |
| Vasculitic | Neutrophilic/lymphocytic infiltration of vessel walls; fibrinoid necrosis; leukocytoclasis; extravasated RBCs | Small vessel vasculitis (HSP/IgA), leukocytoclastic vasculitis, polyarteritis nodosa, urticarial vasculitis |
Pioneered the histological criteria for melanoma staging and established the prognostic significance of tumour-infiltrating lymphocytes (TILs) in melanoma. Mentor to multiple generations of dermatopathologists; contributor to 40+ years of melanoma classification work.
International authority on melanoma diagnosis and Spitz naevus / spitzoid melanoma distinction. Editor of Pathology of Melanocytic Nevi and Malignant Melanoma. Contributor to AJCC melanoma staging committee.
Leading German dermatopathologist and pioneer in the molecular characterisation of cutaneous tumours, FISH analysis of melanocytic lesions, and the pathology of rare adnexal tumours.
Editor of McKee's Pathology of the Skin — the leading comprehensive dermatopathology reference. Expert in cutaneous vascular tumours, soft tissue tumours of skin, and rare mesenchymal neoplasms.
World authority on cutaneous T-cell and B-cell lymphomas. Contributor to the WHO and EORTC classification of primary cutaneous lymphomas. Expert on mycosis fungoides histology and CD30+ lymphoproliferations.
Oncologist-dermatopathologist authority on melanoma biomarkers, PD-L1 expression, and the histopathological assessment of immunotherapy response in melanoma. Chair of the German Melanoma Registry.