An Extremely Rare Case of Renal Collision Tumor Comprised of Hyperpigmented Microcystic Chromophobe Renal Cell Carcinoma and Papillary Renal Cell Carcinoma

Abstract

Abstract Introduction/Objective Renal collision tumors are rare lesions defined as the coexistence of two adjacent but histologically distinct tumors with sharp borders forming a single lesion. A combination of chromophobe renal cell carcinoma (ChRCC) and papillary renal cell carcinoma (RCC) is extremely rare. Here we report a collision tumor of hyperpigmented microcystic ChRCC, an uncommon variant of ChRCC, and papillary RCC. To our knowledge, it is the first reported case of this particular combination. Methods/Case Report A 70-year-old male with aortic stenosis presented with dyspnea and renal insufficiency. A renal mass was discovered incidentally. MRI characterized the left renal mass as 7.2 cm and bilobed. Radical nephrectomy was performed. Grossly, the tumor was located in the upper pole and consisted of two distinct components separated by fibrous tissue: a 5.4 cm black/orange mottled tumor and an adjacent 5.0 cm yellow lobulated tumor. Histologically, the larger tumor displayed a microcystic and solid pattern comprised of large cells with pale cytoplasm, hyperchromatic wrinkled nuclei, perinuclear halos, prominent cell membranes, and extensive intracellular and extracellular brown-black pigment, consistent with hyperpigmented microcystic ChRCC. The adjacent tumor showed diagnostic features of papillary RCC including papillae with fibrovascular cores lined by columnar cells with low nuclear grade, abundant macrophages, and foci of psammomatous calcifications. The hyperpigmented microcystic ChRCC was positive for CD117 and negative for Melan-A. Papillary RCC was strongly positive for Cytokeratin7 and Vimentin. Results (if a Case Study enter NA) N/A Conclusion Meticulous examination of the histologic features, aided by immunohistochemistry, can generate an accurate diagnosis of collision tumor and direct to the appropriate treatment choice.