Skin - tumours

Question 1

HG spindled lesions

Answer 1

AFX (no necrosis, LVI or deep invasion)

spindled SCC

melanoma

leiomyosarcoma

Question 2

low grade spindled lesions

Answer 2

dermatofibroma

DFSP

nerve sheath (neurofibroma, schwannoma, perineurioma)

cellular blue nevus

Kaposi sarcoma

desmoplastic melanoma

Question 3

DF vs DFSP

Answer 3

DF: epidermal hyperplasia, collagen trapping, birefringent collagen, F13a+, CD34-

DFSP: invades subcutis, F13a-, CD34+

Question 4

solitary lesion with lichenoid inflammation

Answer 4

lichen planus-like keratosis

irritated seborrhoeic keratosis

Question 5

solitary lesion with acantholysis

Answer 5

acantholytic acanthoma

warty dyskeratoma

acantholytic actinic keratosis

acantholytic SCC

Question 6

clear cell epidermal neoplasms

Answer 6

clear cell acanthoma

tricholemmoma

SCC in-situ

Question 7

infiltrative skin lesions

Answer 7

infiltrative BCC: clefts, myxoid stroma, pallisading

desmoplastic trichoepithelioma: single lesion, cheek of young women, small keratin cysts

syringoma: multiple, around eyes older women, tadpole shaped ducts

MAC: superficial microkeratocysts, ducts and strands, deep infiltration, PNI

Question 8

junctional lesions

Answer 8

poroma

tricholemmoma (Cowden’s if multiple)

BCC

naevus

Question 9

myxoid skin lesions

Answer 9

digital mucous cyst

digital fibromyxoma

dermal nerve sheath myxoma (s100+)

superficial angiomyxoma (Carney complex if multiple, epithelial component common eg cyst)

myxoid DF

myxoid DFSP (CD34+, PDGFRB mut)

myxoid NF (s100+)

LG fibromyxoid sarcoma (MUC4+, FUS rearranged)

myxofibrosarcoma

Question 10

histiocytoid infiltrate

Answer 10

LCH: CD1a, s100+

JXG: Touton giant cells

lymphoma: atypical lymphoid cells, LCA/T cell markers
mastocytoma: CD117, mast cell tryptase

Question 11

Spitz nevus and pigmented spindle cell nevus (Reed) vs melanoma

Answer 11

Spitz/Reed: symmetrical, Kamino bodies, no Pagetoid disease, HMB45 decrease with depth

Spitz only: crescent clefts, p16+, FISH panel

Question 12

special site nevus - features and melanoma differential

Answer 12

acral nevus: lentiginous component, Pagetoid spread

genital nevus: rete nests, discohesion

both sites (vs melanoma): symmetry, dermal maturation, no deep mitoses

Question 13

Painful skin lesions

Answer 13

ANGEL

angiolipoma (peripheral capillaries with microthrombi)

traumatic neuroma

glomus tumour (SMA+, also glomangioma/glomangiomyoma)

eccrine spiradenoma (cannonballs in deep dermis, 2 cell types)

vascular leiomyoma