Lessons From the Friday Unknowns The patient has a history of systemic mastocytosis with KIT D816 mutation and a small B cell clonal population. Histologic sections show needle shaped fragments of lymph node with clusters of epithelioid mast cells. The infiltrate is paracortical and associated with scattered eosinophils.

Lessons From the Friday Unknowns Microscopic features demonstrates B-cell lymphoma comprised of a mixture of small, intermediate size and large lymphoid cells, with intermediate and large lymphoid cells having one or more distinct nucleoli. Admixed eosinophils are present in some areas. Mitotic division figures are moderately numerous within the intermediate-large lymphoid cells. The lymphoma exhibits…

Lessons From the Friday Unknowns The bone marrow smears and biopsy specimen show extensive lymphocytosis. In smears, the cells have features of hairy cell leukemia variant cells including small nucleoli and moderate hairy cytoplasm.

Lessons From the Friday Unknowns Histologic sections show a very large lymph node. There is extensive capsular sclerosis and there are also perivascular sclerotic bands that course through the parenchyma. The subcapsular sinus is mostly obliterated. The predominant finding is the presence of many lymphoid follicles, many of which have small reactive germinal centers and…

Lessons From the Friday Unknowns Histologic sections show needle shaped fragments of tissue with several foci of necrosis. In one area of necrosis, there are small and large lymphoid cells as well as scattered histiocytes, some with phagocytic activities. Apoptotic bodies and karyorrhectic debris are frequent. In other areas, necrosis is minimal and prominent histiocytic…

Lessons From the Friday Unknowns Histologic sections show needle-shaped fragments of lymph node with an atypical lymphoid infiltrate in a nodular growth pattern and is composed predominantly of small to medium-sized atypical lymphoid cells with irregular nuclear contours and condensed nuclear chromatin, some of the atypical cells accentuating around the reactive follicles with expanded mantle…

Lessons From the Friday Unknowns The specimen consists of multiple fragments of bone marrow and clotted blood. Within some of the fragments, sheets of atypical histiocytoid cells are noted, of intermediate to large size with round to irregular/twisted nuclear contours and prominent nucleolus and slightly eosinophilic, abundant cytoplasm. Some cells look plasmacytoid. There is some…