[RENAL CELL CARCINOMA, PAPILLARY TYPE] – Papillary renal cell carcinoma comprises about 10-15% of all renal carcinomas and shows characteristic genetic abnormalities distinct from conventional clear cell carcinoma including trisomy or tetrasomy of chromosome 7 and 17. The tumor is predominantly composed of papillary projections with or without tubular structures. The papillary configurations may be so complex and packed together that an appearance of a solid growth may ensue.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – The papillary projections consist of a central fibrovascular core lined by a single layer or a pseudostratefied layer of tumor cells. The fibrovascular cores contain variable number of foamy histiocytes and may also show sclerosis.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – Two varieties of papillary carcinoma have been recognized, type 1 and type 2. Type 1 papillary carcinomas account for about 2/3 of all cases and are characterized by a single layer of cuboidal to low columnar cells (arrow) that contain scant to moderate amounts of usually basophilic but uncommonly clear or eosinophilic cytoplasm. The nuclei are round to oval with mild contour irregularity and may contain grooves. Nucleoli are indistinct and frank anaplasia is lacking. Mitoses are sparse.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – Foamy histiocytes (arrow) are commonly identified in the fibrovascular cores and may be numerous in both type 1 and type 2 carcinomas. Note the scant amount of lightly eosinophilic cytoplasm in cuboidal tumor cells lining the fibrovascular core in this type 1 example.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – Foamy histiocytes may be numerous and may cause expansion of the fibrovascular cores. The presence of abundant foamy histiocytes is a helpful diagnostic feature since it is seen almost consistently with papillary renal carcinomas but rarely with other renal cell carcinomas with the notable exception of cystic renal cell carcinoma that may accumulate foamy macrophages.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – Type 2 papillary renal cell carcinoma comprises about 1/3 of the cases and is characterized by larger cells with more abundant and usually eosinophilic cytoplasm than type 1 tumors. Pseudostratification is also more common. Foamy histiocytes are seen in both type 1 and typ2 with about equal frequency and are an important diagnostic finding.
[RENAL CELL CARCINOMA, PAPILLARY TYPE]– One additional morphologic finding of diagnostic importance is the presence of intracellular hemosiderin (arrow) that is not generally seen in other renal carcinomas. Most cells in the type 2 example of papillary carcinoma show predominantly apical hemosiderin granules with basally situated nuclei.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – The tumor cells in some type 2 carcinomas may be intensely eosinophilic with regular round nuclei simulating renal oncocytomas but the presence of papillary architecture, foamy histiocytes, and other morphologic features assist in the diagnosis. The growth is both tubular and papillary in contrast to the nesting, tubular and solid growth pattern seen with oncocytomas. Note the presence of regular, round apical nuclei.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – In this example of type 2 papillary renal cell carcinoma, irregular papillary projections are lined by large eosinophilic tumor cells that focally are pseudo-stratified.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – The cytoplasm can be both eosinophilic and finely granular and tumor cells in urine cytology specimens may be difficult to differentiate from chromophobe renal cells carcinoma and oncocytomas. Note the thin fibrovascular core (arrow) with large cells containing abundant cytoplasm and focal pseudo-stratification of nuclei.
[RENAL CELL CARCINOMA, PAPILLARY TYPE] – Another characteristic histologic feature of papillary renal cell carcinoma is the presence of neutrophils in the fibrovascular cores (arrowhead), which may be numerous in some areas. Neutrophil infiltration is also commonly seen in renal medullary carcinoma.