Primary cutaneous localized/clearly‐outlined true histiocytic sarcoma: Two long‐term follow‐up cases.

Histiocytic sarcoma (HS) is a rare hematopoietic tumor that mainly involves extranodal sites, including the intestinal tract, skin, soft tissues and other organs. It is well known as an aggressive neoplasm that shows a poor response to therapy. However, a subset of patients with resectable disease has shown a favorable outcome with surgical treatment. Primary cutaneous HS is exceedingly rare and, to date, its long‐term prognosis has thus not been well described. Here, we highlight two cases of primary cutaneous HS that showed long‐term survival. Case 1 was a healthy 47‐year‐old woman who found a 12‐mm tumor on her forehead. Case 2 was a 66‐year‐old woman, under follow up of a myxoid liposarcoma in her leg, who presented with a 25‐mm tumor in her hypothenar eminence. Histologically, the tumors in both cases had a smooth outline with proliferating atypical tumor cells that showed histiocytic differentiation as revealed by immunohistochemistry with antibodies to CD68 (KP‐1) and lysozyme in case 1; and CD68, lysozyme and CD163 in case 2. Tumor cells in case 1 had a monotonous appearance. After complete resection, cases 1 and 2 have survived for 10 and 4 years, respectively, without recurrence. To date, such patients are relatively long follow‐up cases of survival from HS and highlight how a clear outline of the primary cutaneous HS tumor may be associated with its resectability and be an important factor in the assessment of its curability. [ABSTRACT FROM AUTHOR]