Pathology of skin tumours

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Normal Skin HistologyStratum CorneumStratum LucidumStratum

GranulosumStratum SpinosumStratum Basale

Stratum basale/germinativum (“basal or “forming” layer)One layer thick mitotic cells10-25% melanocytes with processes into next layerMerkel cells with sensory neurons

Stratum spinosum (“prickly” layer)Cells appear spiny due to numerous desmosomesMany Langerhans cells

Stratum granulosum (“grainy” layer)Cells flattenOrganelles/nuclei begin to disintegrateKeratin precursor granules begin to form

Stratum corneum + Lucidum(“horny” layer)Cells are dead—too far from underlying capillaries

to live20-30 cells thick up to ¾ of dermal thickness

Definitions Hyperkeratosis

Thickening of the stratum corneum, often associated with a qualitative abnormality of the keratin.

ParakeratosisModes of keratinization characterized by the

retention of the nuclei in the stratum corneum.Dyskeratosis

Abnormal keratinization occurring prematurely within individual cells or groups of cells below the stratum granulosum

AcanthosisDiffuse epidermal hyperplasia

Acantholysis Loss of intercellular connections resulting in

loss of cohesion between keratinocytes.

keratocanthoma

Dome-shaped nodule with central keratin plug; 1-5 cm. diameter

Cup-shaped lesion with central crater of keratin; downward pushing rounded border

Higher power keratoacanthoma- large, glassy squamous cells with islands of eosinophilic keratin.

Actinic keratosis

Nuclear abnormalities in basal keratinocytes; dysplasia does not involve full thickness of epidermis.

Histology - SCCIrregular masses of epidermal cells

proliferating into dermisKeratinization in well-differentiated

tumorsRange in degree of anaplasia

In Situ SCCIn situ SCC-type II (moderate) with atypical

keratinocytes extending to the lower two thirds of the epidermis

In situ SCCIn situ SCC-type III (severe) with atypicalkeratinocytes extending more than two thirds

to full thicknessof the epidermis

SCC

Epithelial cells exhibit glassy eosinophilic cytoplasm. Dyskeratotic cells, parakeratosis and horn pearl formation are also observed.

Irregular tongues of dysplastic squamous epithelium invading the dermis

VerrucousMinimal atypiaIndividual cell keratinization

Spindle-PleomorphicAnaplasticLittle keratinization

Adenoid SquamousAnaplasiaAcantholysisTubular &adenoid appearance

Basal Cell Carcinoma

Nests of basaloid cells within the dermis

HISTOLOGY• Large oval

nuclei with little cytoplasm• Nuclei are

uniform• Connective

tissue stroma causes palisading

Histologic SubtypesSolidCysticAdenoidKeratotic (Basosquamous)

Solid – no cellular differentiation

Cystic Differentiation towards sebaceous glands Cystic spaces within tumor lobules

Adenoid varietyGlandular pattern

Baso SquamousShows feature of both basal cell and squamous cell carcinomasMore aggressive clinicallyUndifferentiated cells in combination with parakeratotic cells and horn cysts

Junctional Nevus

Dysplastic compound nevus

Early MM: radial growth in epidermis, superficial dermis

Advanced MM: vertical growth into dermis

Evolution of dysplastic nevus into malignant melanoma over time (not inevitable, but the potential always exists)

Lentigo

Malignant melanoma

Dysplastic melanocytes involve epidermis and invade the dermis

Malignant melanoma, radial & vertical growth phases

Radial growth

Vertical downward growth into dermis

Radial: proliferation of atypical melanocytes laterally within epidermis; Vertical: growth of melanocytes downward, invading into dermis

Superficial spreading

Cell spread along Dermoepidermal jn

Desmoplatic varietyAtypical melanocyte in desmoplastic stroma

Staining with S-100 in desmoplastic melanoma

Nests of small blue cells, with minimal cytoplasm

Electron Microscopy: membrane-bound dense core neurosecretory granules (blue arrows) and stacks of perinuclear cytokeratin filaments (black arrows)

Kaposi sarcomaNumerous atypical, irregularangulated vascular channelsPromontory sign- irregular vascular channels that partially surround preexisting blood vessels.Plasma cells in surroundingStroma - classic finding

Staining for HHV-8 in KSIHC for HHV-8- been shown

99% sensitive100% specific

Densely cellular spindle cells in radially arranged fascicles, invading into subcutis and muscle fibers.

Main portion shows a storiform arrangement with extension into the subcutaneous fat, with fat entrapment creating a honeycomb pattern