Aggressive Cutaneous Lymphomas and Mimics Flashcards
Cutaneous Diffuse Large B-Cell Lymphoma, Leg Type
High-grade malignant lymphoma of post-GC origin. Accounts for 10-20% of primary cutaneous B cell lymphomas.
Occurs in patients between 70-80 years of age with female predominance, most classically on the legs, but also other body sites in 10-20% of cases. Presents as rapidly growing skin plaques or tumors, sometimes with ulceration.
Microscopically characterized by a dense dermal infiltrate of centroblastic/immunoblastic cells with round nuclei and variably prominent nucleoli, extending to the subcutis. Frequent mitoses are present, and necrosis may be seen.
Early lesions may appear as few clusters of perivascular large lymphocytes.
Recurrent or advanced-stage DLBCL-LT retains its leg tropism.
IHC: CD20+, PAX5+, CD79a+, MUM1+, FOX-P1+, BCL-2+. IgM+, sometimes also IgD+. Myc+/-, CD30 +/-. Usually BCL6 +, CD10 negative. Most cases do not show FDC meshworks on CD21/CD23/CD35.
Molecular: MYD88 mutations and NFkB-pathway mutations are classical. BCL2 and MALT1 amplification and CDKN2A/CDKN2B deletion or hypermethylation are also common. Myc rearrangement may be seen.
If BCL2 or BCL6 rearrangement are seen subsequent to Myc rearrangement, the lymphoma is best classified as Double Hit or Triple Hit Lymphoma.
Aggressive epidermotrophic CD8+ lymphoma
Sometimes bears rare fusions, such as PCM1-JAK2.
