Collision Tumor of the Kidney with Clear Cell Renal Cell Carcinoma and Papillary Renal Cell Carcinoma Components: Report of a Rare Case

Abstract

Abstract Introduction/Objective Collision tumors refer to the phenomenon where distinct, well-defined tumor subtypes are present within a single lesion. While this phenomenon has been described in different organs, it has been rarely encountered in renal tumors outside the context of rare tumor susceptibility syndromes. Collision tumors of the kidney may encompass any known benign or malignant renal tumor types. However, a collision tumor of two different renal cell carcinoma (RCC) subtypes is remarkably rare. Methods A 43-year-old male was referred to our institution for the management of a right lower pole renal mass. The right radical nephrectomy specimen revealed a 6.5 x 5.0 x 4.0 cm well circumscribed, yellow-orange and hemorrhagic cortical mass abutting the renal capsule and extending into the renal sinus fat. A grossly distinct 1.5 x 1.4 x 1.2 cm pale, nodular area was demonstrated at the periphery of the tumor. Results Microscopically, the tumor displayed two distinct, neoplastic components within the same mass, without transitional morphology. The majority of the tumor consisted of a nuclear-grade-2 conventional clear cell RCC, while the peripheral nodule represented a type-2 papillary RCC component. Immunostains further supported these findings: The papillary component was strongly and diffusely positive for CK7 and P504S/AMACR with variable EMA and vimentin expression, and negative for CAIX, while the clear cell component was positive for CAIX, EMA and vimentin with only focal and weak staining for CK7 and faint nonspecific P5O4S/AMACR staining. TFE3 Mart1 and HMB45 immunostains were negative in the tumor. Conclusion Collision tumor of the kidney with two distinct RCC subtypes is an exceedingly rare finding. Careful gross examination may be the first clue to identify such lesions, and sampling of all grossly distinct tumor areas is crucial. The identification of collision tumors may have important therapeutic implications, given the difference in pathophysiology and outcome between RCC subtypes.