PMC9879773_01
A solitary non scaly erythematous nodule over the left forearm with a firm consistency measuring 1.5 cm x 1 cm.
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On examination, a solitary nodule over the left forearm measuring 1.5 cm x 1 cm, with an erythematous to hyperpigmented smooth surface and firm consistency (Figure 1).
(A) A dense dermal infiltrate that shows a follicular growth pattern sparing the epidermis and separated by a Grenz zone (arrow) (H&E, 4x). (B) The infiltrate focally extends to the subcutaneous fat (arrow) (H&E, 4x). (C and D) A predominance of small cells with irregular, elongated or angulated nuclei with inconspicuous nucleoli. Larger cells with more rounded nuclei, open chromatin, and peripheral nucleoli are demonstrated (H&E, 40x).
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The infiltrate involved the superficial and deep dermis, focally extending to the subcutis, and sparing the epidermis in a follicular growth pattern (Figure 2).
(A) The neoplastic cells are diffusely and strongly positive for CD20 (4x). (B) They showed variable staining for BCL6 (40x). (C) Uniquely, the neoplastic cells in this case were diffusely positive for BCL2 (4x). (D) CD21 highlights expanded follicular dendritic meshwork (4x).
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Only a few scattered cells were positive for CD10 (Figure 3).