Basicmedical Key

 Can be multiple in some cases • Rare recurrences and association with, or progression to, malignancy [basal cell carcinoma (BCC)] Macroscopic • Nodular lesion involving deep dermis and subcutis • Large, typically >…

 Irregular wrinkled nuclei  Bi- and multinucleation  Perinuclear vacuolization • Old lesions may mimic seborrheic keratoses Ancillary Tests • Immunostain for p16 is negative (there is no overexpression) • In situ hybridization and PCR…

 Female predilection  More prevalent in African Americans • Wide anatomic distribution, usually arises in skin and subcutaneous tissue  Head and neck region common (tongue, oral cavity) • Usually solitary, painless nodule, plaque,…

 Lesions restricted to cutis only rarely metastasize Microscopic • Perpendicularly oriented fascicles of spindle cells • Brightly eosinophilic cytoplasm • Blunt-ended nuclei • Nuclear atypia and mitoses Ancillary Tests • Labels as per smooth muscle:…

 Rare to absent in early lesions, prominent and confluent in late lesions  Nests are irregular in size and shape, randomly alternate with single melanocytes • Cells show elongated, ovoid hyperchromatic nuclei…

 HMWCKs(+), p63; S100(-) • Atypical fibroxanthoma  S100(-); CD10/CD68/CD99 (+) • Dermatofibroma: FXIIIA/CD10 (+); S100(-) • Dermatofibrosarcoma protuberans: CD34(+); S100(-) • Neural tumors  S100/SOX10 (+); CD34(+) (not in DM) • Leiomyosarcoma  Actin/desmin (+), S100(-) Scar-Like Appearance…

Displaced Junctional Nests in Breast NevusAt this low power, a junctional melanocytic proliferation is evident on the breast of a 25-year-old woman. Most nests appear at the tips of rete…

 Malignant T cells rim around adipocytes  Prominent karyorrhexis/apoptosis and angioinvasion Ancillary Tests • Immunohistochemistry: TCRδ1(+), βF1(-), CD56(+), CD4(-), CD8(-) • EBER(-), cytotoxic markers (+) • T-cell receptor gene rearrangement Top Differential Diagnoses • Subcutaneous…

 Pilar type (piloleiomyoma) arises from arrector pili  Genital type arises from specialized genital smooth muscle Etiology/Pathogenesis • Hereditary leiomyomatosis and renal cell cancer syndrome  Multiple leiomyomas of skin and uterus  Subset…

 Solitary circumscribed neuroma (“palisaded encapsulated neuroma”) represents spontaneous proliferation of peripheral nerve fibers  Multiple mucosal neuromas associated with multiple endocrine neoplasia syndrome (type 2B) represents rare autosomal dominant condition  Traumatic…