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…

 Inflammatory component shows variable mixtures of lymphoplasmacytic cells, eosinophils, neutrophils, and histiocytes • Areas with prominent myxoid change • Scattered enlarged atypical tumor cells, some with macronucleoli  Cells with macronucleoli resemble Reed-Sternberg…

 Elongated and anastomosing rete ridges  Atypical basal cells with hyperchromatic-staining nuclei  Subtle abnormal maturation (large, eosinophilic keratinocytes)  Whorling and keratin pearl formation  Usually associated with LS&A  Preferential association with HPV-unrelated…

 Skin metastases: Nodule, often pigmented, may be ulcerated, multiple or solitary  Nodal metastases: Usually in regional lymph nodes  Blue nevus-like melanoma: Blue macule/papule, often near original site of primary melanoma…

 Most patients have good prognosis, with only minority of cases progressing to systemic disease or death Microscopic • Severely atypical/borderline Spitz tumor  Typically, large and deep cellular compound melanocytic tumors  May…

 Genes implicated include PTCH1 (Gorlin syndrome),  TP53, SOX9, BMI1, BAX, RMRP Clinical Issues • Extremely common: Most common cancer in humans • Most common in head and neck region (up to…