Indeterminate Dendritic Cell Sarcoma in a Patient With Myelodysplastic Syndrome

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To the Editor:Indeterminate dendritic cell tumor (IND-DCT), also called indeterminate cell (IC) histiocytosis (ICH), is a neoplastic proliferation of spindled to ovoid cells with phenotypic features similar to ICs. These neoplasms are extraordinarily rare, and little is known about their etiology, pathogenesis, and prognostic factors. The diagnosis remains challenging as their histological classification and phenotypic definition have not been well established. We encountered an unusual case of cutaneous malignant neoplasm occurring in the context of myelodysplastic syndrome (MDS). These tumor cells exhibited an immunophenotypic profile similar to Langerhans cells; in particular, they were CD1a and S100 positive but Langerin/CD207 negative. We proposed a diagnosis of indeterminate dendritic cell sarcoma (IND-DCS) with MDS in this patient.A 77-year-old male patient presented to our clinic with 2 crusted masses, one on his left temporal region and the other on the right inguinal fold. The lesions had been there over 1 year. A biopsy was taken from the right temporal lesion 3 months ago in an outside hospital and was interpreted as an undifferentiated malignant neoplasm. The lesion in the right inguinal fold was excised subsequently 1 month before presentation without histopathologic examination. The patient's medical history was remarkable for leukopenia, resulting from MDS for 5 years and renal insufficiency for 2 years. On physical examination, a 5.0 × 4.5 cm ulcerated and crusted plaque with ill-defined erythematous border was noted on the left temporal region (Fig. 1) and a 2-cm nontender lymph node was palpated on his left neck. An 8-cm linear scar corresponding to the previous surgery was found in the right inguinal fold, as well as a 2-cm palpable lymph node. A peripheral blood count revealed pancytopenia (total leucocytes: 1.04 × 109/L, reference range: 3.90∼9.50 × 109/L; lymphocytes: 0.88 × 109/L, reference range: 1.10∼3.20 × 109/L; neutrophils: 0.09 × 109/L, reference range: 1.80∼6.30 × 109/L; erythrocytes: 1.93 × 1012/L, reference range: 3.80∼5.10 × 1012/L; hemoglobin: 62 g/L, reference range: 130∼175 g/L; platelets: 70 × 109/L, reference range: 125∼350 × 109/L). Other laboratory work-up, including liver function tests, renal function tests, and serum tumor markers (carcinoembryonic antigen, alpha-fetoprotein, carbohydrate antigen 12-5, carbohydrate antigen 15-3, and carbohydrate antigen 19-9), were all within the normal range. Computerized tomography of the chest revealed bilateral pleural effusion; however, cytology of the aspirate failed to reveal malignant cells. Whole-body positron emission tomography–computerized tomography revealed hypermetabolic masses in both the left temporal and right inguinal fold regions, and a diffuse but unevenly increased metabolic rate in the bone marrow. Periodically repeated bone marrow cytology over the following 3 years all consistently showed hyperplasia and morphological abnormalities of the erythrocytic, granulocytic, and megakaryocytic series.The skin biopsy taken from the left temporal region revealed an overlying attenuated epidermis with a dense and diffuse dermal infiltrate (Fig. 2A). At high power, the neoplastic cells revealed pleomorphic nuclei with fine chromatin, conspicuous nucleoli, and abundant eosinophilic cytoplasm. Abnormal mitotic figures were easily identified. Occasional lymphocytes were found mainly at the periphery of the neoplastic sheets, some admixed with neoplastic cells (Fig. 2B). Immunohistochemical study showed that (Fig. 3) the neoplastic cells were strongly positive for CD1a, S-100, CD31, CD68, and lysozyme, focally positive for CD56, and negative for Langerin/CD207, CD3, CD4, CD11c, CD20, CD21, CD33, CD34, CD35, CD43, CD45RA, CD117, CD123, CD163, myeloperoxidase, and Melan A.

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