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Pathology of skin tumours
3
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