Fig. 1

a Computed tomography showed a low-density mass (19× 18 × 22 mm) in the upper pole of the right kidney; b Grossly, a unique well-circumscribed tumor of 2 cm diameter was under the renal capsule. The cut surface was faint yellow and solid; c Histologically, under the ultra low power, the tumor wasclearly demarcated from the surrounding normal renal tissue. (H&E 20×); d In the solid growth area, tumor cells were large and polygonal with abundant eosinophilic cytoplasm. Nuclei were round to oval, prominently enlarged and occasionally bizarre, with prominent nucleoli and amounts of clumped to vesicular chromatin (H&E 200×); e Histologically, in the tubular growth area, epithelial cells showed smaller in size, less cytoplasm and inconspicuous nucleoli (H&E 200×); f Cytoplasmic lumina and nuclear pseudoinclusions were evident. Multinucleated and rhomboid cells were focally noted and corresponded to Fuhrman grade 4 Under the high power, Cytoplasmic lumina and nuclear pseudoinclusions were evident. Multinucleated and rhomboid cells were focally noted and corresponded to Fuhrman grade 4 (H&E 400×); g Immunohistochemically, tumor cells showed diffuse and strong positivity for ALK (D5F3), located in the cytoplasm and cell membrane; h FISH demonstrated that 53% of the nuclei showed either isolated 3′ ALK signals (1R1F, 32%) or break-apart signals (1R1G1F, 21%)