P183 Histiocytic sarcoma of interdigitating reticular cells in the mediastinum - case report

Abstract

Reticular dendritic cells are present in the germinal center of lymph nodes, with the function of pathogens phagocytation. They present antigens to B and T lymphocytes, acting, among other fronts, in the cellular memory. Histiocytic sarcoma is a rare malignant neoplasm with proliferation of cells with morphological and immunophenotypic characteristics of mature histiocytes derived from dendritic cells. In the mediastinum, histiocytic sarcoma of interdigitating reticular cells (HSIRC) are even more infrequent, with only 2 reports in the literature. Its histological diagnosis is considered a challenge, since it must be differentiated from other causes of mediastinal neoplasms, such as lymphomas, germinal tumors, and even lymph node metastases from carcinoma. The report is about a male patient, 69 years old, in schedule of radical prostatectomy due to a prostate adenocarcinoma. In his oncologic staging, he underwent chest tomography that demonstrated a mediastinal tumor suggestive of lymph node enlargement in the right paratracheal chain, of 2.8 cm. The patient was submitted to resection, which showed, in histological analysis, a highly pigmented, slightly differentiated fusiform neoplasm and bands of fibrous tissue, without necrosis and with slight atypia. The immunohistochemical panel showed no specific markers of epithelial, vascular, myogenic, neural or melanocytic histogenesis; In addition, CD21 and CD23 were negative, and CD68 positive. Thus, a diagnosis of HSIRC was made. Surgical resection was the only therapeutic modality performed, currently it is under ambulatory follow-up, with no signs of recurrence. HSIRC is mainly found in lymph nodes, as a localized disease or in disseminated form. It is extremely rare in mediastinal localization. The greatest difficulty reported in this type of sarcoma is its differential diagnosis. Most patients are asymptomatic or have nonspecific symptoms, and imaging is the main diagnostic tool. Current treatment protocols suggest optimal treatment as surgery alone, without radiotherapy or chemotherapy. However, a few studies described in the literature are not enough to guide unequivocally the treatment of these neoplasms. The patient is being followed up in the outpatient clinic for about 6 months after surgery, with no signs of recurrence. In conclusion, this is an extremely rare disease, poorly described in the literature, and should be included among the differential diagnoses of mediastinal lesions.