A 74-year-old smoker male presented with a rapidly enlarging right neck mass, hoarseness, and dysphagia. Thyroid biopsies obtained by open surgery showed a diffuse proliferation of discohesive sheets of large oval and polygonal cells (figure 1 panel A) with round to oval vesicular nuclei. A thorough pathological investigation excluded an epithelial, melanocytic, myeloid, or lymphoid origin hence the morphologic and immunohistochemical findings of positive hemoglobin scavenger receptor or CD163 (figure 1 panel B) and CD68 markers were most consistent with histiocytic sarcoma (HS) [1]. Computed tomography (CT) revealed a locally advanced thyroid mass producing significant deviation of the trachea (figure 1 panel C), and several lung nodules. The patient was started on concurrent radiotherapy to the thyroid and intravenous chemotherapy with cisplatin and doxorubicin with improvement of his presenting symptoms. Interval CT (figure 1 panel D) months after completion of therapy showed a decrease in size of the thyroid mass although there was an increase in size of the lung nodules. Because of the mixed radiological response seen, a CT-guided lung biopsy revealed synchronous poorly differentiated nonsmall cell lung carcinoma. As there are no consensus guidelines for the management of HS due to its rarity, an extensive discussion with the patient took place, and it was decided to commence agents with proven activity against lung cancer with hopes of also achieving some response on his HS of the thyroid. Palliative chemotherapy was given with six cycles of carboplatin, etoposide, and bevacizumab with clinical and radiological stability of lung lesions and his thyroid mass, the latter as documented by positron emission tomography with actual decrease on fluorodeoxyglucose uptake and size of thyroid HS from 8 cm (panel E) to 6.9 cm (figure 1 panel F) in diameter and improvement of the deviation of his trachea. His lung involvement was eventually worsened; hence, the patient was subsequently switched to pemetrexed and bevacizumab until his performance status declined to the point that the patient opted for hospice care ∼16 months after his initial diagnosis. A diagnosis of HS implies a high mortality risk due to rapidly progressive disease despite the use of several chemotherapy agents that usually produce minimal response rates [2]. Our case emphasizes the need for further research in this uncommon disease, which carries dismal prognosis.

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Figure 1. Panel A, Hematoxylin-eosin staining. Panel B, CD163 marker. Panel C and D, computed tomography of the chest showing a thyroid mass with deviation of trachea, and a lung mass. Panel E and F, positron emission tomography showing decrease on fluorodeoxyglucose uptake and size of thyroid mass.

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