Malignant transformation of nasal chondromesenchymal hamartoma in adult: a case report and review of the literature.

Nasal chondromesenchymal hamartoma (NCMH) is an extremely rare benign tumor arising in the sinonasal tract, predominantly involving infants and children. To date, only 27 cases are reported in the international literature and there have been no reported cases of malignant transformation. We present a 40-year-old female patient with nasal obstruction and bloody rhinorrhea. Computed tomography (CT) of the nose and paranasal sinuses confirmed a heterogeneous polypoid soft-tissue mass filling the nasal cavity and extending into the maxillary and ethmoid sinus. The patient underwent a complete radical resection. Histological and immunohistochemical analyses showed a portion of the mass was consistent with typical NCMH. However, some areas of mass exhibited cytological atypia, marked mitotic activity and foci of necrosis. The atypical mesenchymal spindle cells were immunoreactive for vimentin, CD99 and smooth muscle actin (SMA) diffusely. The cartilaginous cells were immunopositive for S-100 protein. Ki-67 index was high in atypical areas, accounting for 50%. A rapid mass recurrence was observed at the original site only 3 months after surgery. The final diagnosis of NCMH with malignant transformation was made. To our knowledge, this is the first report of malignant transformation occurring in an adult with NCMH. Although NCMH commonly develops in the neonate or young infants and exhibits benign histological appearance and favorable prognosis, there is a possibility of malignant transformation in adult patients. Thoroughly histological inspections are suggested to be necessary to accurately diagnose this tumor when it is encountered in adults.