Giant trichoblastoma mimicking malignancy.

We report a case of giant trichoblastoma, a rare benign hair germ tumor. A 73-year-old man presented with a soft-tissue mass on his upper arm. Magnetic resonance imaging analysis revealed an unique mosaic pattern on T2-weighted images. Needle biopsy disclosed a keratinizing tumor suggesting squamous cell carcinoma. The size of the tumor was 9.5 x 7 x 9.5 cm, one of the largest trichoblastomas ever reported. The rarity and gigantic size of the tumor, together with its misleading clinical features, prompted us to report our case.