EXTRANODAL ROSAI-DORFMAN-DISEASE (RDD) OF THE SKIN

A 15-year-old woman presented with a slowly enlarging, tender, right c hest wall mass present for 4 months. The review of systems was unremar kable, specifically for fever, malaise, or adenopathy. On examination, she was well developed and well nourished, with a 4.2 x 2.8 cm hyperp igmented and indurated plaque of the medial right breast (Fig. 1). Thi s lesion was oval, pink-brown, and studded with five to eight light-br own papular excrescences measuring 0.3-0.5 mm each. Induration did not extend beyond the clinically visible lesion. Lymphadenopathy was not present. Complete blood count, blood chemistries, urinalysis, and preg nancy test were within normal limits or negative. Initial biopsy revea led extensive histiocytic infiltration replacing the entire dermis, wi th occasional Touton-type giant cells, in a background of chronic infl ammation, suggestive of benign histiocytic lesion, such as histiocytom a or xanthoma. Electron microscopy revealed a histiocytic infiltrate w ith cells having irregular nuclei, frequent indentations, and prominen t nucleoli. The cytoplasm of the histiocytes contained scattered mitoc hondria, profiles of endoplasmic reticulum, and occasional membrane-bo und dense bodies. She did not return for follow-up until 10 months lat er, as the lesion had become tumorous measuring 7.5 x 10.5 cm (Fig. 2) . Repeat biopsy revealed a multinodular dermal and subcutaneous tumor composed of spindle-and stellate-shaped histiocytic cells varying in n uclear size and staining (Fig. 3a, b). The nuclei were plump and hyper chromatic, with a background of perivascular infiltrates of lymphoid c ells with an admixture of plasma cells. Necrosis was not seen. Occasio nal atypical and multinucleated giant cells were seen having phagocyti zed lymphocytes and neutrophils (emperipolesis) (Fig. 3c). Breast tiss ue itself was not involved by tumor. Special stains revealed the histi ocytic tumor cells to be S-100 and KP-1 reactive, compatible with beni gn histiocytic neoplasm. The tumor was negative for estrogen and proge sterone receptors. The lesion was excised totally and the patient rema ins in excellent health 2 years after surgery, with no evidence of rec urrence.